# Momentum – Pendulums

Momentum – Pendulums

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A pendulum is a weight hanging from a fixed point. A yo-yo on a string can be a pendulum if you have ahold of the string and hold it in one place while the yo-yo hangs down freely. Pendulums are also associated with clocks or hypnotists, who swing an object back and forth from a fixed point. On a swing, YOU are a pendulum. Pendulums are affected by laws of motion. When a pendulum swings it has momentum. In this video, Bill Nye the Science Guy demonstrates momentum:

Things You Need:

• String 3 feet long
• 2 Strings 2 feet long
• Two Mugs
• Two Chairs
• Scissors

This experiment will show you something surprising about how momentum works. Set two chairs back to back about 3 feet apart. Tie a piece of string to the back of one chair and toe the other end to the back of the other chair. The string should not have a lot of slack in it. Tie a 1 foot long piece of string to the piece of string suspended between the two chairs about 18 inches from one of the chair backs. Now tie the other 1 foot piece of string to the suspended string about 18 inches from the OTHER chair back. When you are done, the two pieces of string should be a about 1 foot apart. Now tie a mug to the end of each dangling piece of string. Pull back on one mug and let go, letting it swing back and forth until it stops. Does it stop? What does the other mug do? When you release the first mug, momentum keeps the mug swinging back and forth. The mug will swing until friction in the air and friction from the string knot rubbing on the handle slows it down.

The weird thing is that when the first mug slows down…the second mug will START swinging, even though you never touched it! Some energy from the first mug travels along the string and makes the OTHER mug start swinging. Even though the momentum of the swinging mugs is slowed down by friction, some of the energy is transferred to the string, which carries it to the second mug.

Science Project Idea: Replace the mugs in this experiment with matching objects of different weight. Try two matching plastic mugs. How much momentum do the plastic mugs have? Does the momentum from a plastic mug have enough energy to pass through the string to the second plastic mug? Try hanging two metal forks from the string. Now try two plastic forks. Which kinds of objects have enough momentum to transfer energy to the second object without even touching it?

Here are some books and websites that will help you explore momentum and understand why heavier objects create more momentum:

Words to Know:

Momentum – the product of mass plus velocity. That means the movement that occurs when you consider an object’s mass and how fast it is moving.

Pendulum – A weight hanging from a fixed point.

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# Air Pressure – Straw Through an Apple

Air Pressure – Straw Through an Apple

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Even though air seems like nothing, it really is something. Gases like air, even though they are not visible to our eyes, are made up of molecules just like solid objects. These molecules are pulled toward the earth by gravity.

Earth is surrounded by a layer of air that is heavy. That layer of air exerts pressure on the surface of the earth, a lot of pressure. Our bodies are used to it so it doesn’t bother us. In fact, we are so used to it that what bothers us is when the air pressure is gone.

The higher you go in the atmosphere, the less air pressure there is because the “thickness” of the air is less the higher you go. That’s why airplanes have “pressurized” cabins. We can’t survive in too little air pressure.

Today’s experiment will demonstrate just how strong air pressure is.

What You Need:

• Apple
• Straw

Take a straw and try to push it into an apple. Hard isn’t it? The straw bends. Now put your thumb over one end of the straw while you try to push the other end into the apple. Now what happens?

When you try to push the straw into the apple the air molecules in the straw are squished closer together. If your thumb is not over the opposite end of the straw the air molecules just spill out the end. However, if your thumb IS over the opposite end of the straw the air molecules are trapped. All those packed together molecules make the straw stay stiff so that it can push into the apple. The straw seems empty, but it isn’t, it is full of air molecules.

Here are some websites and books that will help you undertand air pressure:

Words to Know:

Air Pressure – The force exerted by the weight of air. Air pressure is the weight of the earth’s atmosphere as it sits on the earth’s surface.

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# Heated Gases Expand – Ivory Soap

Heated Gases Expand – Ivory Soap

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When a substance is heated it’s molecules move faster. You can see this in a pot of water when you heat it on the stove. As the water gets hotter its molecules begin to move until the water is boiling.

When gases are heated, the same thing happens. As gas is heated up the amount of space the gas takes up increases. You can see this by heating up a bar of soap.

You have to use a bar of soap that floats. To make sure you have a bar of soap that will work, float it in a bowl of water. A bar of soap will float because it has air bubble whipped into it. Ivory soap will work for this experiment.

What You Need:
Bar of Soap that Floats
Bowl of Water
Paper Plate
Microwave

Break or cut the bar of soap into four pieces. Put the pieces on a paper plate and microwave for 1 minute. Watch the ivory soap through the microwave window.

As you heat the soap molecules in the air bubbles move quickly away from each other, or expand. This is called Charles’s Law. The same thing happens when you pop popcorn or cook a marshmallow .

Sciece Experiment Idea: Choose different kinds of soap to see what will happen when they are heated up for one minute in the microwave. Be sure to heat each bar of soap up on the same kind of plate and make sure you heat each bar for the same amount of time. The variable in this experiment is the soap, everything else has to be the same. Do the bars of soap each react the same way when they are heated up in the microwave? Why do you think so? Tip: Choose ivory soap for one of your trials – it’s cool!

Here are some books that will help you learn about and experiment with heated gases:

Words to Know:

Atoms – The smallest, most basic unit of matter. An atom is made up of a nucleus surrounded by electrons.
Molecules At least two atoms held together by a chemical bond.
Charles’s Law – as temperatures of a gas increase, so does its volume. Simply, heated gases expand.
Heat – to make hot or warm.

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# Nucleation – Mentos Volcano

Nucleation – Mentos Volcano

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What You Need:

• Liter of Diet Soda
• Roll of Mentos Candy

Definitely go outside. Set the liter of soda on a firm surface – a sidewalk will work fine. Quickly – and I mean quickly – add the roll of mentos candy. Stand back!!

Soda is fizzy because it has carbon dioxide pumped into it at the soda bottle plant. The carbon dioxide bubbles just sit there in the soda until you open the top. When you open the top some of the bubble escape making that “whisssssh” sound.

Each mentos candy has a bunch of pits on the surface. The pits are so small you can barely see them. Under a microscope the a mento would look like a golf ball. Those little pits on the surface of the mento are a perfect place for a bubble to form, this is called a nucleation site.

When you drop the candies in the soda they sink and also start making bubbles in all of those pits. The bubbles form and explode making the soda bubble up and out the top of the soda bottle.

Here are some websites and books that will give you more chemical reaction experiments to try:

Words to Know:

Nucleation Site A place where a gas can form bubbles.

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# Melting Point – DIY Slushie

Melting Point – DIY Slushie

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What You Need:

• Your Favorite Drink (Soda, orange juice, lemonade, etc.)
• Quart-size zip-lock bag
• Gallon-size zip-lock bag
• 2 cups ice
• 1/4 cup salt
• Bowl

Fill the quart size bag with your favorite drink and zip it closed. HINT: Make sure the bag is zipped really good or your slushie will taste bad when some of the salt leaks into your bag. Put the quart size bag inside the gallon bag. Add the ice and salt to the gallon bag. Zip the gallon size bag closed. Now shake the bag a lot – even play catch with it…gently. In about 15 minutes you will feel the ingredients in the quart size bag starting to firm up. What started out as a liquid is changing to a solid. When it feels done take the quart size bag out of the gallon size bag. Rinse it off good in clean water. Then open the bag, squeeze the slushie into a glass and enjoy!

TIP: It’s OK for a dog to lick the ice, it won’t be in your drink anyway. Tip for the dog…lick the ice BEFORE the salt goes in!

And if you’re feeling like something with a few more ingredients, try this, ziploc bag ice cream!:

Your favorite drink is a liquid until it gets really cold.  Your liquid drink would be pretty good with ice just floating in it…the ice cubes would make the drink colder…but the ice cubes would not make the drink freeze into a slushie.

Ice forms when the temperature of water is 32 degrees or colder. You don’t want the ice cubes to melt IN your drink, you want your DRINK to turn slushie. In order to make your drink turn slushie you have to get it really cold. Salt lowers the melting point of water. To make a slushie you want the temperature around the bag of your favorite drink to be lower than 32 degrees so your drink will freeze. When you add salt to the ice cubes you lower the melting point of the ice cubes by several degrees. The ice cubes stay colder, longer – long enough to turn your drink slushie. Your salt/ice mixture will make your slushie faster than your freezer! That secret is the catalyst – the salt.

Science Experiment Idea: Make 3 different quart size bags each filled with the exact same amount of your favorite drink. Fill each of three gallon size bag with the exact same number of ice cubes. Add 1/8 cup of salt to the first gallon size bag and label it with a sharpie, “1/8”. Add 1/4 cup of salt to the second gallon size bag and label it “1/4”. Add 1/3 cup of salt to the third gallon size bag and label it “1/3”. Have a couple friends help you shake and smoosh the bags to make the slushies. Time how long it takes each of the bags to turn into a slushie. Which amount of salt makes a slushie the fastest?

Here are some websites and books that will help you understand the thermodynamics of slushies…and ice cream too!

Words to Know:
Heat – To increase in temperature.
Melting Point – The temperature at which a substance will change from a solid to a liquid.
Thermodynamics – The study of the transfer of heat.
Catalyst – Something that makes a change happen faster.

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