Baking Soda & Vinegar Volcano

Use baking soda and vinegar to create an awesome chemical reaction! Watch as it rapidly fizzes over the container and make sure you've got some towels ready to clean up.

What you'll need:

• Baking Soda (make sure it's not baking powder)
• Vinegar
• A container to hold everything and avoid a big mess!
• Paper towels or a cloth (just in case)

Instructions:

1. Place some of the baking soda into your container.
2. Pour in some of the vinegar
3. Watch as the reaction takes place!

What's happening?

The baking soda (sodium bicarbonate) is a base while the vinegar (acetic acid) is an acid. When they react together they form carbonic acid which is very unstable, it instantly breaks apart into water and carbon dioxide, which creates all the fizzing as it escapes the solution.

For extra effect you can make a realistic looking volcano. It takes some craft skills but it will make your vinegar and baking soda eruptions will look even more impressive!

 

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Cut Ice Cubes in Half Like Magic

Speed up the melting process of ice with the help of a little pressure. Cut a piece of ice in half like magic while learning how the process relates to ice skating.

What you'll need:

• One ice cube
• A piece of fishing line with a weight (the heavier the better) tied to each end
• A container
• Some kind of tray to keep things from getting wet

Instructions:

1. Turn the container upside down and put it on the tray.
2. Place the ice cube on top of the upside down container.
3. Rest the fishing line over the ice cube so that the weights are left dangling over the side of the container.
4. Watch it for around 5 minutes.

What's happening?

The pressure from the two weights pulls the string through the ice cube by melting the ice directly under the fishing line. This is similar to ice skating where the blades of a skater melt the ice directly underneath, allowing the skater to move smoothly on a thin layer of water.

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Make a Tornado in a Bottle

Learn how to make a tornado in a bottle with this fun science experiment for kids. Using easy to find items such as dish washing liquid, water, glitter and a bottle you can make your own mini tornado that’s a lot safer than one you might see on the weather channel. Follow the instructions and enjoy the cool water vortex you create!

What you'll need:

• Water
• A clear plastic bottle with a cap (that won't leak)
• Glitter
• Dish washing liquid

Instructions:

1. Fill the plastic bottle with water until it reaches around three quarters full.
2. Add a few drops of dish washing liquid.
3. Sprinkle in a few pinches of glitter (this will make your tornado easier to see).
4. Put the cap on tightly.
5. Turn the bottle upside down and hold it by the neck. Quickly spin the bottle in a circular motion for a few seconds, stop and look inside to see if you can see a mini tornado forming in the water. You might need to try it a few times before you get it working properly.

What's happening?

Spinning the bottle in a circular motion creates a water vortex that looks like a mini tornado. The water is rapidly spinning around the center of the vortex due to centripetal force (an inward force directing an object or fluid such as water towards the center of its circular path). Vortexes found in nature include tornadoes, hurricanes and waterspouts (a tornado that forms over water).

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Blowing Up Balloons With CO2

Chemical reactions make for some great experiments. Make use of the carbon dioxide given off by a baking soda and lemon juice reaction by funnelling the gas through a soft drink bottle and in to your awaiting balloon!

What you'll need:

• Balloon
• About 40 ml of water (a cup is about 250 ml so you don't need much)
• Soft drink bottle
• Drinking straw
• Juice from a lemon
• 1 teaspoon of baking soda

Instructions:

1. Before you begin, make sure that you stretch out the balloon to make it as easy as possible to inflate.
2. Pour the 40 ml of water into the soft drink bottle.
3. Add the teaspoon of baking soda and stir it around with the straw until it has dissolved.
4. Pour the lemon juice in and quickly put the stretched balloon over the mouth of the bottle.

What's happening?

If all goes well then your balloon should inflate! Adding the lemon juice to the baking soda creates a chemical reaction. The baking soda is a base, while the lemon juice is an acid, when the two combine they create carbon dioxide (CO2). The gas rises up and escapes through the soft drink bottle, it doesn't however escape the balloon, pushing it outwards and blowing it up. If you don't have any lemons then you can substitute the lemon juice for vinegar.

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Design and Test a Parachute

Learn about air resistance while making an awesome parachute! Design one that can fall slowly to the ground before putting it to the test, making modifications as you go.

What you'll need:

• A plastic bag or light material
• Scissors
• String
• A small object to act as the weight, a little action figure would be perfect

Instructions:

1. Cut out a large square from your plastic bag or material.
2. Trim the edges so it looks like an octagon (an eight sided shape).
3. Cut a small whole near the edge of each side.
4. Attach 8 pieces of string of the same length to each of the holes.
5. Tie the pieces of string to the object you are using as a weight.
6. Use a chair or find a high spot to drop your parachute and test how well it worked, remember that you want it to drop as slow as possible.

What's happening?

Hopefully your parachute will descend slowly to the ground, giving your weight a comfortable landing. When you release the parachute the weight pulls down on the strings and opens up a large surface area of material that uses air resistance to slow it down. The larger the surface area the more air resistance and the slower the parachute will drop.

Cutting a small hole in the middle of the parachute will allow air to slowly pass through it rather than spilling out over one side, this should help the parachute fall straighter.

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Oersted's Experiment

Hans Christian Oersted was a Danish scientist who explored the relationship between electric current and magnetism. Current is the flow of electrons, and is how we hardness electricity. Currents create their own magnetic fields in closed loops, which magnets are known to induce, or create current, in wires.

Oersted experimented with this, using a compass, which uses the magnetic poles of the Earth to show your which direction you are facing. By bringing the compass near a closed current loop, he was able to interfere with the magnetic field and cause the compass needle to move.

Problem

Observe electromagnetic induction by recreating Oersted’s Experiment.

What will happen when you bring the compass towards the current loop?

Materials

• D battery
• Insulated wire
• Electrical tape
• Compass
• Box
• Electical tape

Procedure

1. Cut a 1 meter loop of insulated wire.
2. Use electrical tape to secure a stripped end of the wire to one side of a D battery.
3. Run the wire up one side of the box, across the top, and down the other side. Make sure you have enough wire so that itcan run along the table or ground to reconnect the battery. Now you have a loop!
4. Connect the other open end of the wire to the battery so current begins to flow.
5. Bring the compass into the center of the loop. What happens?
6. Move the compass around closer to the wire and away from the wire. Record your observations.

Results

The wire will carry a current that creates a magnetic field around itself. Bringing the compass near the wire or in the loop will cause the compass needle to move.

Why?

The current will induce a magnetic field based on the right-handrule. Make a “thumbs-up” sign with your right hand. The thumb will be the direction of the current (flowing from the negative to positive terminal of the battery) and the fingers will curve around in the direction of the magnetic field.

The magnetic field created by the current will interfere with the magnetic field the compass experiences when it is brought near enough.

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How to Make a PVC Pipe Instrument

Sound is a neat thing. It’s really just vibrations in the air, but with it you can hear music, speech, movements, actions, trains, planes, and cars. Sound is often measured by its frequency. Frequency is measured in cycles per second with a unit called a hertz.

We describe sound as a wave; specifically, a compression wave. What that means is that sound travels as a force that gets transmitted through air molecules with an initial push. These pushed molecules bump into other air molecules and then bounce back, and they do this at a certain frequency, or rate. Sound travels a lot like the way movement travels through a slinky.
The pressure of air due to sound waves in a pipe (like a flute) looks a lot like a sine wave. If you have a pipe with an open end and a blocked end, the blocked end (often called the node) of the pipe doesn’t let the air change pressure much. An unblocked pipe also has a node, located in its center. The distance between nodes determines the frequency of sound wave vibration, and the higher the frequency, the higher the pitch. Let's learn how to make a PVC pipe instrument to see all of these concepts in action.

Problem

Make an instrument out of PVC pipe.

Materials

• Pencil & paper
• PVC pipe (½ inch Schedule 40, 4 feet or so)
• Duct tape
• Pennies
• Ruler
• Hacksaw
• Sandpaper (optional)
• Electronic tuner (optional)
• Adult

Procedure

Note: Read all the instructions and do your math before cutting your pipes!

1. First, we need to do some calculations. Musical notes are all produced by sounds of specific frequencies. You can translate those frequencies to tube lengths using the speed of sound. Here’s how:

2. To find out the length of tube you’ll need to produce a given note, insert your measurements (in inches) for tube diameter and the frequency of your desired note (in Hertz). The speed of sound (at sea level) is 13,397.244 inches per second. Plug these numbers in and solve for the length of the tube in inches. Here’s an example:

3. You can use the internet to look up frequencies and choose any notes you want, but here’s a list of notes at certain frequencies to get you started. For the above calculation, we solved for the tube length necessary to produce a D at 587 Hz (which gives us a tube length of about 12.65 inches).
4. D: 587 Hz, E: 659 Hz, F: 698 Hz, G: 784 Hz, A: 880 Hz, B: 987 Hz, C: 1046 Hz
5. Have an adult help you measure and cut a length of pipe to match each note you’ll include in your scale. Make sure your pipes are cut slightly longer than you need so you can cut them down to tune them.
6. Blow over the edge of the pipes (or slap one end with your hand) and use the tuner or just listen to hear if they’re the right length. Sand or saw them down as needed.
7. Sand down one end of each pipe so that so that each pipe’s outside surface tapers down a sharp edge at the inside surface. This will make your pipes sound better.
8. Line up your pipes side by side in order of ascending length, and duct-tape them all together securely. Make sure that all of the sanded ends are lined up as well.
9. Play some notes! Rubber flip flops make great mallets to strike your tubes with.

Results

You made a pipe instrument that allows you to play notes on a musical scale.

Why?

What’s happening is called resonance: moving particles are forced to vibrate a specific number of times per second. You can change resonance by changing the length of your pipe. Let’s talk about why.
In air, the speed of sound is about 768 miles per hour. If you bump one end of an open pipe, you create a pressure wave that rides from one end of the pipe to the other. The pressure wave actually overshoots the open ends of the pipe, creating low pressure areas that draw air from inside the pipe. This begins another cycle with rarified air. This keeps happening back and forth until the wave dies down due to friction. Since sound has a characteristic speed, the number of times that this high-pressure/low-pressure cycle happens per second is directly dependent upon how long the tube is because it takes a certain amount of time for the pressure wave to get from one end to the other.

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Simple Harmonic Motion: Pendulum

The movement of a pendulum is called simple harmonic motion: when moved from a starting position, the pendulum feels a restoring force proportional to how far it’s been moved. Put another way, it always wants go back to where it started.

Pendulums move by constantly changing energy from one form to another. Because of this, they are great demonstrators of the conservation of energy—the idea that energy doesn’t just appear or disappear; it always comes from (or goes) somewhere. The reason pendulums don’t move forever is because eventually, all the energy ends up transferred to the surrounding environment. But what if you could capture some of that lost energy? This fun demonstration does just that: you’ll use a pendulum to move energy from one place to another.

Problem

Use two pendulums to observe energy being moved around within a system.

Materials

• Several feet of string
• Scissors
• Weights that can be tied to the string (e.g. heavy washers or nuts)

Procedure

1. Cut a length of string several feet long (roughly 4 to 5 feet). Attach both ends to the ceiling or the underside of a table—any place that will allow the loop of string to dangle freely. Tie the ends far enough part so most of the slack is taken out of the string, and identify the midpoint of the string.
2. Cut two more equal lengths of string, each about a foot long. Tie a weight to one end of each string. Tie each loose end to the long, hanging string 6 inches away from the hanging string’s midpoint.
3. Steady the weights so that everything is still. Take one of the weights and pull it several inches towards you, away from the long string, and then gently let it go.
4. As the weight swings back and forth, watch the other weight. What do you notice? Does the second weight move? Does its motion change over time? How does the motion relate to the first weight? What happens to the first weight’s motion?
5. Simply observe the motion of the weights for a couple of minutes. Describe what you see.

Results

At first, the second weight remains stationary while the first weight swings back and forth. Slowly, the second weight will start to move; its motion will be opposite that of the first weight. The arc of the second weight’s swing will get larger as the first weight’s gets smaller. Eventually, the second weight will be the only weight swinging. If you keep watching, the process will reverse itself until the second weight stops and all the motion returns to the first weight.

Why?

This experiment shows energy being transferred back and forth between the pendulums. When you pull the first pendulum towards you, you put potential energy into the system: energy that is stored away but not actually doing anything yet. As soon as you release, the potential energy rapidly starts converting to kinetic energy—the energy of motion—as gravity pulls the weight in an arc. At the bottom of the swing, all the potential energy is gone; the pendulum’s energy is entirely kinetic. Then, as the pendulum starts to climb again, the kinetic energy starts transforming back into potential energy until it has climbed as far as it can go. The energy keeps sloshing back and forth like that on every swing: potential turns to kinetic which turns back to potential, over and over.

Pendulums, like all simple harmonic oscillators, are great demonstrators of the conservation of energy: the idea that energy cannot be created or destroyed, only transferred. The energy you end up with has to equal the energy you start with. But if that’s true, how does the second pendulum start moving? Where does its energy come from? Easy: it comes from the first pendulum.

During every swing, a little bit of energy is transferred into the long string the two pendulums dangle from. Start the pendulum swinging again. This time, watch the longest string: it moves! As the pendulum oscillates, it tugs on the string. The string, in turn, tugs on the second pendulum. A tiny fraction of the first pendulum’s kinetic energy goes through the string and displaces the pivot of the second pendulum, causing the second pendulum to swing—and with every swing, a little more energy gets transferred from one pendulum to the other.

Eventually, the first pendulum has no more energy to give to the second pendulum. When this happens, the first pendulum stops, while the second pendulum swings away—but now, the second pendulum pulls on the string. The energy starts working its way back to the first pendulum until eventually, the balance of energy is right back to where it started.

This can’t continue forever. With every swing, energy is also lost to pushing the air out of the way or vibrating whatever the main string is attached to. No system is perfect. Eventually, all the energy you provided is lost to the environment and both pendulums will stop swinging.

Going Further

Experiment with pulling more or less on the first pendulum. How does that affect how far the second pendulum ends up swinging? Do the pendulums swing for longer?

What if you replace the main string with something rigid, like a beam or a dowel? Does the second pendulum start moving? What do you think is going on here?

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Building a Better Battery

Did you know that you could build your own battery, using nothing more than some dimes, pennies, paper towels, and lemon juice? In this science project, you can use your homemade battery to make the needle on a compass move. You can also figure out which variables in building the battery will make the needle move the farthest.

Problem:

How a battery can be made from everyday materials?

Materials:

• Paper towels
• Scissors
• Ruler
• Pennies
• Lemon juice
• Dimes
• Insulated wire
• Nail
• Compass

Procedure

1. Cut out small squares from the paper towels, each one one-inch square.
2. Place a penny on the table.
3. Soak a paper towel square in lemon juice and place it on top of the penny.
4. Place a dime on top of the paper towel square.
5. Continue this process to build a small tower that includes five pennies, five paper towel squares, and five dimes.
6. Coil the middle portion of insulated wire around and around the nail, leaving both ends free.
7. Touch one of the free ends to the top of the stack and another of the free ends to the bottom of the stack.
8. Move the nail close to the compass. The needle on the compass should move. Measure exactly how far it moved. (You can also use a volt meter for this experiment for more accurate results. See if you can borrow one from a nearby science lab.)
9. Build other towers using smaller stacks, larger stacks, and stacks using multiple paper towel squares between each layer. Which technique makes the needle move the farthest? Why do you think this may be?

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Faraday's Experiment

Michael Faraday was a 19^th century English scientist who is credited with many great discoveries in the realm of physics and chemistry, specifically on the relationship between current and magnets, and electrochemistry.

Current is the flow of electrons from one place to another, and is how electricity is carried. Currents are known to create their own magnetic fields, and the movement of magnets is known to induce, or create, current in a wire. In this lab, you will recreate Faraday’s famous experiment by building a solenoid (a coil of wire) and experimenting with magnets to produce current.

Objective

Induce current in a wire with a magnet.

Hypothesis:

What will happen when you pass a strong magnet through a loop of copper wire?

Materials

• Bar magnet
• Insulated copper wire
• Galvanometer (sensitive current-measuring device)
• Cardboard paper towel or toilet paper tube

Procedure

1. Wrap the copper wire tightly around the cardboard tube to create a solenoid. Wrap as many times as you can and be sure to leave a few inches at each end to connect to the galvanometer.
2. Connect each loose end of the wire to the positive and negative terminals of the galvanometer.
3. Switch on the galvanometer.
4. Insert the magnet inside the cardboard tube and move it around. What happens? Record your observations.
5. Try moving the magnet faster or slower. What happens?
6. Turn off the galvanometer and disconnect one of the terminals.
7. Reduce the number of turns in the solenoid. Reconnect and switch on the galvanometer.
8. Insert the magnet inside the cardboard tube and move it around again. What happens? Record your observations. Does the number of coils affect the amount of current generated?

Results

The faster the magnet moves, the more current is generated in the loop. The same is true of the coils: the more coils in the solenoid, the more current generated.

Why?

In Faraday's experiment, the magnet exerts a force from a distance (within the tube) and acts on the electrons to move them around. This is easy with copper wire because the electrons move around with little resistance (explaining why copper is such a great conductor). It is important that the wire forms a closed loop (complete circuit) or this will not work! The magnetic field acts on all parts of the loop in slightly different ways, due to the direction of the magnetic field. The field pushes the current in one direction or the other, depending on which pole of the magnet is approaching. This can be figured out with the right-hand-rule.

A “thumbs-up” motion is made with the ride hand. The thumb represents the direction of the magnetic field and the curve of the fingers is representative of the direction of the current in the loop.

Motors and generators use magnetic movement to create current and send electricity to do useful work to power machines. Auroras in the sky are caused by particles being electrically charged by the magnetic field of the Earth. Electromagnetism is both useful and beautiful!

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Magnetic Linear Accelerator

Have you ever seen one of those roller coasters that shoots out of the station at an insanely high speed? These roller coasters don’t need to climb hills first to use gravitational potential energy—their power comes from magnetism and energy conservation.

A series of electromagnets (magnets made by pumping electrical current through coils of wire) alternately push and pull on the rollercoaster, pumping up its speed pretty quickly. Some engineers have imagined using the same idea to launch objects into space (from, say, a base on the Moon) without using rockets.
In this project, you’re going to build a very simple magnetic accelerator to launch steel balls at targets. What could possibly go wrong?

Problem

Build a simple magnetic linear accelerator.

Materials

• Wooden ruler with groove along the middle
• Four small, powerful magnets (e.g., neodymium magnets)
• Nine steel balls, roughly 5/8” in diameter
• Tape
• Hobby knife
• Safety Goggles

 Procedure

1. Place the ruler (flat side down) on a table.

2. Lay one magnet in the ruler groove, about 2.5” from the ruler’s end. Use the tape to secure the magnet to the ruler and the knife to trim the tape to the size of the magnet.

3. Repeat step 2 with each of the remaining three magnets, placing each about 2.5” away from the preceding magnet.
4. To the right side of each magnet, place two steel balls in the groove.

5. Place a “target” a few inches to the right of the ruler. Your tape dispenser will work fine.

 

6. Place the ninth ball in the groove on the far left end of the ruler (opposite the target).

 

7. Put your safety goggles on.
8. Let the ball go and stand back!

Results

The ball will be attracted to the first magnet and set off a chain reaction of balls firing between the magnets until the last one flies off the ruler at high speed to strike its target.

Why?

What you just saw is a fantastic example of energy conservation. Energy from one ball gets transferred to the next, and then to the next, and so on. But where is all the energy in the last ball coming from if the first ball starts off from rest?
The answer is in the magnets.
Before the starting ball is released, there is potential energy stored up between the ball and the first magnet. The magnet and ball feel an attractive force, but your finger is preventing anything from happening. Once you let go of the ball, it gets drawn towards the magnet (which won’t move because it’s taped down). Potential energy gets converted to kinetic energy—the energy of motion. This is no different then holding a ball in the air and letting it go.
Eventually the ball strikes the magnet—but where does all that energy go? Well, it gets transferred to the balls on the other side of the magnet. The ball closest to the magnet is held pretty tight, but the second ball is farther away and doesn’t feel as strong an attraction to the magnet. This means there’s enough kinetic energy from the first ball to send this ball flying off with nearly the same amount of energy. (That’s why we need two balls stuck to the other side of the magnet: to lessen the attractive force a bit. Try getting it to work with only one ball loaded up next to each magnet and see what happens.)
This second ball is launched at roughly the same velocity as the first ball achieved. As this second ball gets drawn to the second magnet, the attractive force causes it to accelerate and hit the second magnet at a higher velocity than the first ball hit the first magnet. The third ball takes off with the highest velocity achieved by the second ball, and since it gets accelerated by the third magnet in turn, it strikes third magnet faster and harder than the first two balls struck their respective magnets.
Are you seeing a pattern begin to emerge? With each added magnet, more kinetic energy accumulates in each launched ball. The last ball takes off with the combined kinetic energies of all the balls that came before it!
In principle, you can add more rulers and magnets and get the final ball moving as fast as you like—up to a point. Eventually, the balls would be moving fast enough to break the magnets, a limit for which I’m sure your target is very thankful.

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Centripetal and Centrifugal Force

Have you ever wondered why you don’t fall out of an upside down loop on a roller coaster, or why a satellite can stay in orbit around the earth? Centripetal force is a force that causes an object to move along a curved path by pulling the object towards the center of the path. The velocity (speed and direction) of the object is constantly changing because the direction of the object is constantly changing, even though the speed remains the same unless acted upon by an outside force. The direction of such an object at any given point is always perpendicular to the centripetal force.
For a circle, the centripetal force is given by the following equation:
F = ma_c = (mv² / r)
Where F is the force in Newtons, m is the mass of an object in kilograms, and a_c is the centripetal acceleration which can also be described by v²/r, the square of the velocity divided by the radius (the distance from the center of the circle).
For objects traveling in a vertical orientation, meaning at some point they are upside down, the centripetal force must be at least equal to the gravitational force, so the object (or person!) does not fall.

Objective:

Observe centripetal force in action, and use the centripetal force equation to predict the results of the experiment.

Hypothesis:

What will happen to the water in the bucket when the bucket is spun faster? Slower?

Materials:

• Plastic bucket with handle
• Scale
• Large jug
• Water
• Meter stick
• Notebook and pencil

Procedure

1. Measure your arm from the shoulder to your hand. When spinning the bucket, this will be the radius of the circle. Record the length in meters.
2. Weigh the bucket on the scale. Record the weight.
3. Place the large jug on the scale and record the weight.
4. Pour water into the jug and record the weight. Subtract the weight of the jug to get the weight of the water alone.
5. Convert the weight of the water into kilograms. Why is it important that the mass is in kilograms?
6. Pour the water into the bucket.
7. Go outside to an area where it is okay to spill water. With your arm fully extended, swing the bucket around in circles.
8. Swing the bucket slower and slower until the water spills out.
9. Using the centripetal force equation, calculate the velocity of your spin for the mass of water in the bucket. How do you solve for velocity? What is significant about this force? This velocity?
10. Repeat the experiment with different masses of water, or even different radii by tying a rope to the bucket handle.
11. Compare centripetal force to gravity exerted on the water. How much water can you swing for a given velocity?

Results:

The water will spill out of the bucket when the gravitational force of the water exceeds the centripetal force exerted on the water when it is upside down.

Why?

Centripetal force exerted on a spinning object like our bucket of water also leads to an equal and opposite centrifugal force, an apparent force that draws a rotating object away from the center of rotation (thus holding the water in the bottom of the bucket as it passes overhead). Centrifugal force is a consequence of inertia—the tendency of a moving object to want to continue moving in a straight line. As we fling our bucket of water in an arc over our head, the water wants to continue traveling in a straight line, but our string constantly redirects the water so it travels in an arc instead! Water’s inertia resists this redirection, leading to the apparent force that “pulls” the water into the bottom of the bucket. It’s a great example of Newton’s third law: The string pulls on the water to change its direction from a straight line to an arc (centripetal force), and the water’s inertia pulls back (centrifugal force)!
Here’s an analogous situation: Imagine you’re riding as a passenger in your dad’s car. He makes a really sharp turn, and as a result, you feel like you’re being thrown against the inside of the car door. What’s really happening is that your body wants to continue moving forward, but the turning car pulls your body in a new direction. Your body’s intertia resists this pull, because like all objects, it wants to continue traveling in a straight line.
Now, let’s take a look at the math.
To solve for velocity of your swinging bucket, you have to calculate the gravitational force that acts on the water:
F_g=mg
Where F_g is the gravitation force in Newtons, m is the mass of the water and g is the acceleration due to gravity, which is 9.81m/s on Earth.
The water will spill from the bucket when the gravitational force is slightly greater than the centripetal (or centrifugal) force, so for simplicity they can be set to equal each other, the variables rearranged, and solved. It is important that weight (mass) is measured in kilograms because that the units in the equation must be consistent for the equation to be true.

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Hooke's Law: Calculating Spring Constants 

 

Forces cause objects to move or deform in some way. Newton’s third law states that for every force, there is an equal and opposite force. This is true for springs, which store and use mechanical energy to do work.
Springs are elastic, which means after they are deformed (when they are being stressed or compressed), they return to their original shape. Springs are in many objects we use on a daily basis. They in ball point pens, mattresses, trampolines, and absorb shock in our bikes and cars. According to the Third Law of Motion, the harder your pull on a spring, the harder it pulls back. Springs obey Hooke’s Law, discovered by Robert Hooke in the 17^th century. Hooke’s law is described by:

F = -kx

Where F is the force exerted on the spring in Newtons (N),
k is the spring constant, in Newtons per meter (N/m),
and x is the displacement of the spring from its equilibrium position.
The spring constant, k, is representative of how stiff the spring is. Stiffer (more difficult to stretch) springs have higher spring constants. The displacement of an object is a distance measurement that describes that change from the normal, or equilibrium, position.

Problem

Calculate the spring constant using Hooke’s law.
Which spring do you think will have the greatest spring constant? The smallest spring constant? Why?

Materials

• Scale (measures grams or kilograms)
• Ruler (measuring centimeters)
• Different coil springs
• Small weight
• Wooden plank
• Table or countertop
• Books, or other stackable objects

Procedure

1. With the help of an adult, fix one end of each spring to one side of the wooden plank. Be sure to leave a couple of inches between each spring. Why should one end of the spring be fixed?
2. Arrange some books on a table or countertop in two stacks, about the length of the wooden plank.
3. Place the wooden plank on the stacks with the springs hanging down. Make sure there is still some room between the bottom of the springs and the table.
4. Using the centimeter side of a ruler, measure the equilibrium position of each spring.
5. Weigh the small weight on the scale and record its mass in kilograms. Why does the mass have to be in kilograms?
6. Attach the weight to each spring one at a time, and use the ruler to measure the displacement. An easy way to do this is to measure the length of the spring, and then subtract the equilibrium length.
7. Calculate the gravitational force exerted by the mass on the spring.

F_g = mg

Where F_g is the gravitational force, in Newtons, m is the mass of the weight, in kilograms, and g is the gravitational constant of Earth, equal to 9.81 m/s².
Set the gravitational force (F_g) equal to the force exerted by the spring (F). Why can you make these two variables equivalent? Use Hooke’s law to calculate the spring constant, k, for each spring.

Results:

Springs with larger spring constants will have smaller displacements than springs with lesser spring constants for the same mass added.

Why?

Hooke’s Law is a representation of linear elastic deformation. Elastic means that the spring will return to its original form once the outside force (the mass) is removed. Linear describes the relationship between the force and the displacement. The fact that the spring constant is a constant (it is a property of the spring itself), shows that the relationship is linear.
Of course, Hooke’s Law only remains true when the material is elastic. If a spring is permanently deformed (by something like crushing or overstretching), it will no longer return to its original position. If you have ever played with a slinky and accidentally stretch it too far or bent it out of shape, you’ll know that it doesn’t perform like it is supposed to afterward.
For Hooke’s Law to work properly, the parts of the equation have to be in the correct units. Without consistent units, the equation is meaningless.
You can set the gravitational force exerted by the mass on the spring equal to the force exerted by the spring due to Newton’s Third Law of Motion, which states that forces come in pairs. Every force has an equal and opposite force.

 

 

 

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Physics of Pool: Elastic Collision of Equal Masses

The final shot in the pool game is yours, but the cue and the eight ball aren’t nicely lined up with any of the pockets. Looking around, the closest pocket is 45 degrees off the line between the two balls. You take aim for a glancing blow, the cue ball strikes the eight ball…what happens next? Do you sink the eight ball? Which way does the cue ball end up going? And how can you make the eight ball go off in a different direction?

Pool is a great example of physics in action. After every collision, the momentum of all the balls—the product of their mass and velocity—has to be conserved. That is, the total momentum before the collision has to be the same as the total momentum after the collision. And, roughly speaking, the energy must be conserved as well; the balls can’t fling away from each other with more energy than you give them. These two laws—the conservation of energy and the conservation of momentum—work together to steer the balls around the table.
In this project, you’ll experiment with colliding masses, see how they collide, and maybe learn how to use physics to plan the perfect pool shot!

Problem

At what angle will two equal-mass balls move away from one another after a glancing collision?

Materials

• 2 low friction masses of equal weight (hover pucks orair hockey pucks would work best)
• Smooth, flat surface (if using a pool table, try placing a foam board overthe surface to reduce friction)
• Protractor
• Tape
• String

  Procedure

• Place one puck on the surface and mark its starting position with the tape.
• Place the second puck a foot or so away from the first puck.
• Gently push the second puck towards the first puck, aimed so that it hits the puck at a glancing angle rather than straight on (this may take a few practice runs).
• Mark a couple of points along the paths both pucks tookafter the collision.
• Using the marks as a guide, lay a lengthof string along each of the paths taken by the pucks.
• Use the protractor to measure the angle between the strings—the angle at which the pucks moved away from each other.
• Repeat steps 1-6 several times and calculate the average angle between the strings. If the puck doesn’t hit at a glancing angle, then just skip that attempt and try again.

Results

The angle between the pucks’ paths will be close to ninety degrees—a right angle.

Why?

In an elastic collision, both momentum and kinetic energy are conserved. Momentum is given by mvand kinetic energy by ½mv², where m is mass and v is velocity. If ​​v_crepresents the velocity of the moving puck before the collision, ​​v_ais the velocity of the moving puck after the collision, and ​​v_bis the velocity of the stationary puck after the collision, then conservation of kinetic energy leads to:

½mv_c²=​½mv_a² + ​½mv_b²

Because all the masses are equal, the m’s cancel and you end up with:

v_c²=v_a^{2 +}v_b²

This equation has the exact same form as the Pythagorean Theorem, c² = a²+ b²​where a and b are the sides of a right triangle and c is the hypotenuse. This only works if v_aand v_bare at right angles to one another.

 
The conservation of momentum adds some depth (and complexity). Momentum is a little more complicated because it has to be broken down into components: the momentum along the original direction of motion (x) and momentum perpendicular to that direction (y). Momentum in both directions has to be conserved. Initially, all the momentum is in the x direction:

mv_cx = mv_ax + mv _bx

Canceling the masses, you end up with

v_cx = v_ax + v _bx

In the y direction, there is initially no momentum. To make everything balance, that means the y-direction momentums after the collision must perfectly cancel:

mv_cy = 0 = mv_ay + mv _by

0 = v_ay + v _by

v_ay = -v _by

Putting this together with the conservation of energy, you find that all the velocity components after the collision have the same magnitude, with the y components pointing in different directions. You end up with the final velocities pointing at right angles away from each other.
In an inelastic collision, kinetic energy is not conserved; some energy is lost to the surroundings. This means that, while the ycomponents of the velocity still have to cancel, the xcomponents can be different. The balls will no longer bounce away at right angles.
In reality, perfectly elastic collisions rarely happen; some energy is always lost. Collisions between subatomic particles (protons and electrons) are very nearly elastic; so are atoms in an ideal gas. Space probes that slingshot around a planet behave the same way as elastic collisions as well.

Going Further

What happens if you use pucks (or balls) with different masses? For example, if you’re using air hockey pucks, try making the stationary puck be two pucks stacked on top of one another. What changes?
What happens if you use a surface that isn’t smooth (for example, a carpet)? How does that change the angle? Is it less than or more than a right angle? Can you explain what you’re seeing using the equations mentioned above?

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Evaluating Choice Blindness: Do You Know What You Want?

“Choice blindness” refers to the phenomenon where people are blind to their own choices or preferences and are able to validate decisions they did not actually ever make. This experiment will evaluate whether men or women are more likely to demonstrate choice blindness.

Problem:

This experiment will evaluate whether the phenomenon of “choice blindness” occurs more often with men or women.

Materials:

• Approximately 30 test subjects (15 men and 15 women)
• 20 photos of non-celebrity, unknown (to test subjects) males
• 20 photos of non-celebrity, unknown (to test subjects) females
• Notebook for recording results
  

  Procedure

• Recruit 15 male and 15 female adult test subjects.
• Print 20 photos of non-celebrity, unknown males and 20 photos of non-celebrity, unknown females. The photos should be headshots that are approximately the same size, zoom, brightness, etc.
• Present two male photos side by side and ask a female test subject to tell you which person she finds more attractive.
• Take both photos away and present her with her chosen photo. Ask her to tell you why she chose that image.
• Record her answer.
• Repeat steps 3-5 ten times with the female test subject using different pairs of faces each time. In three of the trials, however, exchange one face for the other after the test subject makes her choice. In these three trials, closely observe your test subject. Does she notice that she is presented with the photo that she did not choose? Is she able to give a reason why she chose that photo (even though she actually did not choose the photo)?
• Repeat this experiment withall of your male and female test subjects. For your male test subjects, use the non-celebrity, unknown female photos that you chose.
• Analyze your results. How many times were you able to fool your female test subjects by presenting them with photos they did not choose? How many times were the male test subjects fooled? What conclusions can you draw about choice blindness in men and women?

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Density Experiment

Density refers to the amount of stuff there is in a given space. Different things have different densities. For example, a cup of water has more stuff in it than a cup of oil. The water is denser. A marble and a ball of the exact same size are made of different amounts of stuff – they have different densities. Do you think the less dense oil will sink in or float on the denser water? Which is denser, the marble or the ball? How can you tell?

Problem:

How do liquids of various densities interact with each other?

Materials:

• Measuring cup
• Clear glass jar (labels removed)
• ½ cup water
• Food coloring
• ½ cup corn syrup
• ½ cup vegetable oil
• Marble
• Small rubber ball of approximately the same size as marble
• Circle of carrot, mini marshmallow, other small objects

Procedure

1. Pour the water into the jar.
2. Color it with food coloring.
3. Pour the corn syrup into the jar. What happens?
4. Carefully pour the oil into the jar. What happens?
5. Drop the marble into the jar. Does it float? Sink?
6. Drop the ball into the jar. Does it float? Sink?
7. Continue dropping objects into the jar and observing what happens.
8. What can you tell about the densities of the liquids and the objects?

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Does the Amount of Air Inside the Ball Affect How Far It Goes?

Objectives

To determine whether the amount of air in a soccer ball will affect how far it goes when kicked.

 

Materials and Equipment required

• Soccer ball
• Ball pump
• Ball pressure gauge
• Tape measure meter or yardstick
• Inflation needle
• Glycerin oil
• Roll of gym floor tape
• Marker
• Pen
• Graph paper
• Data chart

Introduction

This soccer science fair project serves to acquaint students with basic information on how the amount of air in a soccer ball can affect the distance it travels when kicked with a consistent force. The greater the air pressure in the ball, the farther it will travel when a force is applied. In the process of conducting the research, the student will learn that atmospheric pressure may also affect how far the ball will travel. The student will learn about the relationship between air pressure and friction: the lower the friction, the farther the ball will go. The student will learn about concepts like air pressure, gravitational force, compression and expansion of air molecules, potential energy and kinetic energy.
This science fair experiment also serves to acquaint students with the essential processes of scientific inquiry such as using a control, of identifying dependent and independent variables, collecting data, presenting data, and making good judgments about the validity and reliability of their findings.

Research Terms

• air
• friction
• forces
• air pressure
• compression of air molecules
• expansion of air molecules
• gravitational force
• energy
• kinetic energy
• pressure gauge
• air pump

Research Questions

• How do we measure air pressure?
• How much air pressure is there at sea level?
• How is air pressure inside the ball related to the distance the ball will travel?
• What happens to the air pressure inside the ball when it is kicked?
• Will the atmospheric pressure affect the distance the ball will travel?
• Does friction affect the distance the ball will travel?

Terms, Concepts and Questions to Start Background Research:

• What is a control? A control is the variable that is not changed in the experiment.
• What purpose does a control serve? It is used to determine what the variable changed.
• What are variables? Variables are factors that can be changed in an experiment.
• What is an independent variable? The independent variable is the one that is changed in the experiment.
• What is a dependent variable? The dependent variable is the one that changes as a result of the change in the independent variable.

Experimental Procedure

1. State the problem you are going to investigate in this science fair project.
2. Create and reproduce the data sheets you will use to record your observations.
3. Gather all your materials.
4. Select a helper (another student or a parent) to assist you in gathering the data.
5. Use the gym floor tape and mark the path along which you will kick the ball.
6. Select three air pressure levels for the ball, designating them as low, medium and high. Using the pressure gauge, double check the pressure in the soccer ball each time you change the pressure. Caution: When kicking the ball, try to kick with the same force each time. Have your partner mark the spot where the ball lands each time. Then, measure the distance and record the data in your chart. Repeat the procedure 3 times at each pressure level and then average and record the results for each level.
7. Make a line graph of the data, recording differences in pressure on the Y axis and the distance travelled on the X axis.
8. Record your conclusion and prepare your report. Include all of the following: a clear statement of the problem, your hypothesis, and a list of the materials used. Include any safety precautions taken. Describe the procedures used. Include all the data that were gathered, including all charts and graphs. For dramatic value, you may include photos of the materials used or of you in the process of conducting this investigation. Include a bibliography of sources you used. You may wish to assess what you did and describe what you would do differently if you were to do this project again. You may wish to expand this research next year. What other experiments might you use to investigate the physics of a soccer ball?

Charting and or Graphing Data

In each section of the experiment, use charts to display the obtained data such the following sample:

Chart #1 : Observations: How far did the ball go?

Pressure in soccer ball in PSI	Distance Travelled in cm.
High #1
High #2
High#3
Medium #1
Medium #2
Medium#3
Low #1
Low#2
Low#3

Chart #2: Average Data

Pressure	Averages
High PSI
Medium PSI
Low PSI

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Can You Cook Using Only Sunlight?

Grade Level: 7th to 11th; Type: Meteorology, Physics

Objective:

Bake cookies with an oven that collects sunlight and traps heat.

• How can I cook using just sunlight?

Make an oven that collects sunlight and traps the shorter wavelengths (heat!) inside the same way greenhouse gases in our atmosphere trap them, and bake some cookies!

Materials:

• Two cardboard boxes: one must fit completely inside the other with about an inch or two to spare, and the outer one must have flaps (or you can create and attach some)
• Roll of aluminum foil
• Masking tape
• Four 12-inch pieces of string
• Eight beads or pieces of macaroni
• Pencil
• Piece of black construction paper
• Scissors
• Scrunched-up shredded paper
• Piece of glass, large enough to completely cover the smaller box but small enough to fit inside the larger one
• Cooking thermometer
• Small cookie sheet or pie tin (must fit inside smaller box; make your own with some of the foil if necessary)
• Prepared cookie dough (commercial or homemade) that bakes at 350° or under warm, sunny day

Experimental Procedure

1. Cover the insides of the flaps of the larger box with aluminum foil, with the shiny side facing out; tape the foil in place. Use the pencil to poke small holes in the edges of the flaps.
2. Tie a bead to one end of one of the pieces of string, string it through one of the holes in one of the flaps so that the bead ends up on the outside of the flap, string it through the hole in the next flap over from the inner side to the outer, and tie another bead to this end of the string. Repeat so that all four flaps are connected together with the strings.
3. Line the entire inside of the smaller box with foil, shiny side out, taping it in place.
4. Cut the piece of construction paper so that it fits neatly inside the smaller box; tape it inside the bottom of the box.
5. Put enough shredded paper inside the larger box so that when you rest the smaller box on it, the opening is just barely below the opening of the big box.
6. Center the little box and pack the space between the walls of the big box and the walls of the little box with more shredded paper.
7. Put the cooking thermometer and some of the cookies on the baking sheet (you may need to grease it first: check the instructions/recipe) and set it inside the inner box; cover the inner box with the pane of glass. Your solar oven is ready to go!
8. Take the oven outside and set it in a bright, sunny spot where it won’t be disturbed. Turn it so that the sun shines directly into it; if the sun isn’t pretty close to directly overhead, you might want to put something under one side of the box to tip it to face the sun. Use the strings to adjust the flaps so that as much sunlight as possible is reflected into the inside of the oven.
9. Now you wait. I hope you brought a good book! Depending on the time of day and how warm it is outside, you may need to turn the oven or even move it to a new spot so that it gets as much sunlight in it as possible.
10. Keep an eye on the cooking thermometer. You’ll notice that it gets much hotter inside the oven than it is outside. That’s partly because the aluminum foil is focusing the solar radiation, and partly because the glass is acting like a layer of greenhouse gases: like them, it’s clear, but some of the shorter wavelengths will bounce off of it and tend to stay inside the oven, making things hotter and hotter inside. It may get as hot as 350° Fahrenheit in there!
11. When the cookies look like they’re about done (they’ll probably be browning around the edges and won’t be shiny anymore), or when the thermometer reads a temperature higher than they’re supposed to cook at, whichever comes first, take the glass off and let the inside of the oven cool for a few minutes. When the cookie sheet isn’t too hot to touch anymore, lift it out and try a cookie!

Terms/Concepts: solar radiation, greenhouse gases

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Crystal Fudge

Grade Level: 8th to 12th; Type: Geology

Objective:

Find out what happens when the fudge crystallizes at different temperatures.

Research Question:

• Why do some rocks that are made out of the same minerals have different-sized crystals in them?
• What effect will faster vs. slower cooling have on the formation of crystals?

Fudge is one of very few desserts people make at home that is actually crystalline, or made out of crystals. This gives us a fun, tasty way to explore the process of crytalization.

Materials:

• Two bread pans (disposable 8” pie tins will also work)
• Butter to coat pans, or waxed paper
• Large saucepan (3-4 quart)
• Wooden spoon
• Candy thermometer
• Pastry brush
• Stove
• Refrigerator
• 3oz. unsweetened chocolate
• 3c sugar
• 1c warm half-and-half or evaporated whole milk
• 1T corn syrup ¼t salt
• 3T butter
• 2t vanilla extract
• 1c mix-ins of your choice: nuts, mini marshmallows, dried fruit… (optional)
• Magnifying glass

Experimental Procedure

• Butter the pans or line them with the waxed paper.
• Mix the chocolate, sugar, salt, half-and-half, and corn syrup over medium-low heat. Keep stirring until the chocolate is melted and the fudge begins to boil. Note: the fudge is extremely hot at this point, handle with care!
• As soon as the fudge begins to boil, stop stirring and put the candy thermometer in. Clip it to the edge of the pot, making sure the tip isn’t touching the bottom.
• Let the fudge cook without any stirring until it reaches the soft-ball stage, around 237 degrees.
• While the fudge cooks, dip the pastry brush in a little warm water and use it to carefully wash any sugar/chocolate/whatever off the sides of the pot.
• Take the fudge off of the burner and let it cool, undisturbed, until it’s 150 degress.
• Add the vanilla and butter and keep stirring until the surface of the fudge starts to get dull. This can take a long time, but you need to keep stirring! Maybe you can get a partner to help.
• Once the fudge has begun to dull, stir in your add-ins, a quarter-cup at a time, if you’re using any. Make sure they’re at room temperature or a little warmer if possible.
• Spoon half of the fudge into each pan. Put one pan in the refrigerator and leave the other one out at room temperature. Allow both of them to cool completely.
• Cut each panful of fudge into one-inch cubes. Pick up a cube from each pan and examine them closely. Use your eyes and the magnifying glass: do you see any differences in texture? Use your tongue: does one seem more smooth and waxy while the other is more grainy? Is there a difference in flavor? The fudge that cooled more slowly, at room temperature, should be grainier and have noticeable sugar crystals in it. This is like a plutonic igneous rock that has cooled and solidified slowly, under the surface, like granite. The one that cooled more quickly, in the refrigerator, should be smoother and have much smaller crystals, probably too small for you to see even with the magnifying glass. This is like a volcanic igneous rock that cooled quickly above the earth’s surface, like obsidian.
• Now offer samples of each to your family and friends so they can decide which they like best!

Terms/Concepts: igneous rock; crystallography, crystal formation

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What Music Does Bacteria Enjoy the Most?

Grade Level: 9th to 12th; Type: Biology

Objective:

This experiment will explore whether music of different varieties affects the growth of bacteria.

Research Questions:

• Does music alter the growth of bacteria?
• Do different kinds of music make the bacteria grow differently?

Although bacteria lack the ability to hear, they are very perceptive to changes in vibration. Physically speaking, music is essentially various changes in vibration. This experiment might help figure out better ways to process sewage and other essential microbe-assisted duties.

Materials:

• 2 or more prepared Petri dishes with agar (available from biological supply companies)
• Sterilized swabs
• Rubber or plastic gloves
• 2 or more portable CD or MP3 players
• Several pairs of cheap headphones, NOT earbuds (same number as music players) You will want to throw them away after the experiment.
• Several songs or albums of various music, the more diverse the better (such as classical, hard rock, and dance)
• Camera
• Notepad and paper
• Ruler

Experimental Procedure

1. Wearing gloves, prepare the Petri dishes. Following the manufacturer’s instructions, take them out of the refrigerator for about an hour before conducting the experiment.
2. Using the sterilized swabs, collect bacterial samples while wearing gloves. Good places to nab some bacteria include faucets or any other area that is touched by a lot of people. Ensure that you swab from the same area to get roughly the same amount and type of bacteria. Swipe the swab against the agar in the Petri dish and then close and seal the dish. Label each sample.
3. Place the samples in a warm, out of the way place. Leave one sample alone, this is the control.
4. For the other samples, place the headphones snugly around the dish.
5. Connect the headphones to the music players. Play a different song or album on repeat on each player.
6. Let the samples grow for a week. Make sure to keep the music players charged and playing at all times. Take pictures of the developing bacteria everyday.
7. Take off the headphones and compare each sample. Take note of the amount of colonies in each sample and measure the size of each colony.
8. Carefully dispose of the Petri dishes.
9. Analyze this data. Did the music have an affect on the size or amount of bacteria colonies? Did a certain genre of music have a greater affect than others?

Terms/Concepts: microbiology, bacteria, microbes, vibrations, sewage treatment

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Laser Jet Toner: a Magnetic Fluid

Grade Level: 7th to 9th; Type: Physical Science

Objective:

In this experiment, you will experience a magnetic fluid as it moves, bubbles, and forms unique shapes.

Research Questions:

• Why does the fluid contort into different shapes?
• Are there other fluids that are magnetic?
• What makes them magnetic?

Materials:

• Magnets of varying size and strength
• Laser jet toner (Ferro fluid)
• Beaker
• Pure vegetable oil
• Stirring stick
• Long, clear bottle, jar or flask

Experimental Procedure

1. Pour 50mL of toner into the beaker.
2. Pour in 30mL of pure vegetable oil.
3. Stir it to a nice thin consistency. (If it is too thin, it might not work properly.)
4. Pour the mixture into the long container.
5. Touch a magnet to the container. Observe what happens to the fluid. (It should move with the magnet and contort into intriguing shapes.)
6. Experiment with using other magnets. See what happens when you drop the magnets into the liquid.

Terms/Concepts: magnetism, magnetic fluid

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When Air Masses Collide

Grade Level: 7th to 10th; Type: Meteorology
Objective:
Use hot and cold water to simulate what happens when a warm front meets a cold one.

Research Questions:

What happens when a warm air mass meets a cold one?

Materials:

• Pencil and paper
• 10-gallon aquarium
• Piece of cardboard
• Scissors
• Stirrer (a wooden spoon or a ruler would be great)
• Five gallons of very cold water
• Blue food coloring
• Five gallons of very hot water
• Red food coloring
• Timer or clock
• Latex gloves
• Red colored pencil, crayon, or marker
• Blue colored pencil, crayon, or marker

Experimental Procedure

1. Use the pencil to draw seven large rectangles that look something like the aquarium on the piece of paper. Label the seven rectangles “0 minutes,” “1 minute,” “3 minutes,” “5 minutes,” “7 minutes,” “10 minutes,” and “15 minutes.”
2. Cut the piece of cardboard so that it just barely fits inside the aquarium, dividing it in half the short way. It should be very snug; it needs to keep the water on one side from mixing with the water on the other side for a minute or so. But don’t use any tape to keep it in place, it needs to come out easily!
3. With the cardboard snugly in place, fill half of the tank with the very cold water. (If it’s ice water, so much the better, but don’t get any ice in the aquarium.) Put a few drops of blue food coloring in the water and stir it; repeat as needed until you’re happy with the color. This is going to represent the cold front, or mass of cold air.
4. Now carefully fill the other half of the aquarium with very hot water and stir in some red food coloring. This is your warm front, or warm air mass.
5. Quickly draw a picture of what the tank looks like now by using the red and blue pencils to fill in the rectangle marked “0 minutes.”
6. Put on the gloves and quickly and carefully remove the sheet of cardboard. Try not to stir the water up too much in the process. Set the timer for one minute, remove the gloves, and watch what the water does until the timer rings.
7. Set the timer for two more minutes, then quickly draw a picture of what the water looked like at the one-minute mark in the rectangle labeled “1 minute.”
8. When the timer rings, set it for two more minutes and sketch what the tank looked like at the three-minute mark.
9. Repeat, setting the timer for the appropriate number of minutes (watch out, that changes toward the end) until you’ve filled in all of your rectangles.
10. Now look at your pictures. What did the “air masses” do? Did they mix right away? Was there a sharp division between them, or did the water combine and make a purple layer? Did the air masses stay side by side as they blended, or did one rise while the other sank? Why do you think the cold and warm fronts behaved the way they did?

Terms/Concepts: air mass, warm front, cold front

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