# Potential & Kinetic Energy – Marshmallow Catapult

Potential & Kinetic Energy – Marshmallow Catapult

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Every object on earth has potential energy. That means it COULD move even if it isn’t right now. When an object IS moving it has kinetic energy.

In today’s demonstration you are going to store energy in a spring. That spring will have the potential to move, but it won’t move until you let it move. The catapult you make is going to transfer energy from the spring to a marshmallow. The marshmallow will have potential energy until the catapult releases, then the marshmallow will have kinetic energy as it flies through the air.

You Will Need:

• Kleenex Box & 2 pencils OR 10 popsicle  or craft sticks
• Rubber Bands
• Milk Jug Cap

Directions:

Here are some websites and books that will help you understand energy:

• US Energy Information Administration: What is Energy?
• Physics4Kids: Energy Around Us
• ENWIN Utilities: Types of Energy
• Gadgets and Gizmos Chapter on Energy “Energize” (pages 111-136).  Marshmallow Catapult (Pages 120-122).
• Science Experiments That Fly and Move (pages 12-13) Marshmallow Shooter

Words to Know:

Energy – the ability to move things or do work; a force acting through a distance.
Potential Energy – Stored energy.
Kinetic Energy – The energy of motion.
Catapult – A device used to throw an object…like a slingshot or a medieval catapult the knights at a castle might use.

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# Engineering – Build a Bridge

Engineering – Build a Bridge

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What You Need:

• Dry Spaghetti, Fetuccine, Straws or Bamboo Kabob Skewers
• Small Gumdrops,  Small Marshmallows or Square Carmels

Here are some websites and books that will help give you great ideas for designing and building your own bridge. Make a simple design and then try to build it with different materials. Which materials work best? Can you figure out why?

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# Gravity – Stacking

Gravity – Stacking

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Gravity is the force that pulls objects toward the center of the Earth. Gravity can make things fall down but it can also help hold things in place. You probably have some games at home the show you a lot about the power of gravity. One of those games is Jenga – that game where you stack up the pieces of wood into a tower and then take turns sliding one of the wood pieces out of the stack. The other game is Cup Stackers – that game where you make a pyramid of the cups as fast as you can and then take it down again. The cups and the wood blocks make strong towers if the base of the tower is wide. This keeps the tower stable.

What You Need:

• Several Plastic or Paper Drinking Cups or Blocks

Build a tower by stacking the blocks or cups one on top of the other. If you are using cups, alternate them so that every other cup is upside down. The towers built from single objects stacked on top of each other don’t get very tall before they tip over do they? Now stack the cups or blocks in a pyramid. Depending on how many cups or blocks you have, the pyramid tower can get pretty tall without tipping over. This is because the weight of the cups or blocks is distributed across a wide base. It’s kind of like the difference between balancing on one foot or balancing on two feet. The wider the base, the more weight that can be supported before gravity will pull an object or stacked objects down.

Here are some websites and books that will help you explore gravity:

Words to Know:

Gravity – The force that pulls everything toward the center of Earth; the force of gravitation on Earth.

Weight – A measure of the force of gravity upon an object

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# Chromatography – Black Ink

Chromatography – Black Ink

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Black ink is black, right? Today you are going to find out. In this experiment you will be able to see all of the dye colors that mix together to make black ink.

What You Need:

• Paper Towel or Coffee Filter
• Bowl
• Water
• Several different kinds of black markers

Cut strips from the paper towel about 1 inch wide – one for each type of marker. Scribble across the bottom of one of the paper towel strips with each kind of marker. Scribble about one inch from one end of the paper towel strip. Tape the OTHER end of the strip to the maker you used to scribble on that strip. That will help you remember which marker goes with each paper towel strip.

Now hang the paper towel strips above the bowl of water so that only a little bit of the scribble end is in the water. Do not submerge the pen scribbles! Check on the paper towels in an hour. What has happened to the pen marks?

What you see happening on the paper towel strips is called chromatography. The color of the ink in markers is made by mixing different pigments together. A pigment is a substance that makes color, like ink or dye. To make black, several pigments are mixed together. When the end of the paper towel strip is submerged in water the water soaks up through the paper towel. When the water passes through the black ink marks it takes the pigment colors with it. Different colors of pigments travel with the water at different rates because the molecules of some pigments stick to the paper more strongly than others. So, as the water travels it separates the colors. This is called chromatography – separating the parts of a mixture so that you can see them one at a time. It looks like there is more than one way to make black!

Here are websites and books that will help you understand solutions and experiment with chromatography:

Mixtures and Solutions Chromatography (pages 34-38)

Words to Know:

Chromatography A process that separates a mixture by passing it through something that will separate its parts.
Mixture – A substance made by mixing two or more substances together. The molecules of the substances don’t join together so the substances can be easily separated.
Homogeneous Mixture – A type of mixture that is the same throughout. Salt water and ink are good examples.
Pigment – A substance used for coloring; ink, dye, etc.

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# Center of Gravity – Fork on Glass; Balanced Pop Can

Center of Gravity – Fork on Glass; Balanced Pop Can

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Gravity is the force that pulls objects toward the center of the Earth. An object’s center of gravity is the average location of the weight of the object.

If you have a wooden ruler you can balance it on your finger at the 6 inch mark. The ruler has a uniform shape and it’s weight is evenly distributed along its shape. It is easy to determine that the 6 inch mark, right in the middle, is the center of gravity for the ruler. There is an equal amount of weight on each side of the 6 inch mark; the gravitational pull on both sides of the rule is equal – so the ruler will balance.

If you have an object like a person trying to balance on a balance beam, then it is a little trickier to figure out where the center of gravity is located. It will be a little different for each gymnast depending on how their weight is distributed on their body. Each gymnast learns the location of their own center of gravity and knows to keep that point centered over the balance beam. If that point is not centered, the gymnast will fall off.

In today’s experiments you will find the center of gravity for objects that are not as easy as a ruler, you will find the center of gravity for a pop can and a fork.

What You Need:

• an Empty Soda Can

Here is a video that will show you exactly what to do to balance a pop can:

I tried the pop can and it really did work. It only took a couple tries too. It is a little harder to tap it and make it go in a circle.

Balancing the two forks is a little harder.

What You Need:

• Two Identical Forks
• Toothpicks
• Salt Shaker
• Empty Pop Can
• Water

First, stick a toothpick in the center hole of a salt shaker. This will act as your balance point. Now take the two forks and press the tines of the two forks together, making them into an “L” shape. Hold a toothpick in your hand and try to balance the forks on the toothpick. Once you get the forks balanced, transfer them from the toothpick you are holding to the toothpick stuck in the salt shaker. The girl in the video makes it look easy. Not easy!

Here are some websites and books that will help you understand and play with gravity:

Words to Know:

Gravity – The force that pulls everything toward the center of Earth; the force of gravitation on Earth.
Center of Gravity The average location of the weight of an object.
Weight – A measure of the force of gravity upon an object
Balance – An even distribution of weight so that an object will remain upright and steady even if it is resting on a very small point.

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