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Every object on earth is made of atoms and gravity pulls these atoms to the earth. You can measure the pull of gravity on an object – we call that measurement weight.

Density  is how close together the molecules of a substance are or how much mass a substance has in a given space. If you have one cup of jelly beans and one cup of marshmallows…the jelly beans have more mass…there is more “stuff” compacted into the cup. The marshmallows are mostly air. If you put each of those cups in a microwave to melt…the sugar and water that makes up the jelly beans would almost fill the cup to the top. The sugar and water that makes up the marshmallows would only fill the cup a little bit because marshmallows have less mass, they are mostly made of air. Materials with more density weigh more. A cup of jelly beans weighs more than a cup of marshmallows.

For an object to be bouyant, or float, it must have less density that what it is floating in, or it has to have something attached to it that helps it float – like you with a life jacket on.

You Will Need:

• Drinking Glass
• Clear Soda
• Water
• Ten Raisins

Fill one clear glass up with water and drop in five raisins. Fill another clear glass up with clear soda like sprite or 7up. Drop in five raisins. What happens when you drop the raisins in? What a few minutes – now what is happening to the raisins in each glass? Can you guess why the raisins are behaving differently?

Raisins are heavier than the water in the drinking glass. The raisins are also heavier than the soda in the drinking glass. At first, both sets of raisins sink to the bottom of the glass, they don’t float.

But the soda has little air bubbles in it – the carbination. These bubbles are attracted to the rough surface of the raisens and stick there. When there are enough of these little carbonated balloons (the bubbles) stuck to the raisins the bubbles lift the raisins to the surface making the raisin float, like little temporary life jackets. When the bubbles pop and the gas inside them escapes into the air…the raisins don’t have anything to help them float anymore and they sink to the bottom of the glass again.

• PBS Kids: Fetch Float My Boat
• NOVA Online: Buoyancy Basics
• Highlights: What Makes People Float?
• Science Bob: The Magic Ketchup Experiment
• Kids Science Challenge: That Sinking Feeling
• Fetch Potion Commotion
• ZOOM Activity: Water Density
• Activity TV: Double Density
• Virtual Mass, Volume and Density Lab
• ZOOM Dancing Raisins
• ZOOM Dancing Raisins 2

Here are some books to help you learn about bouyancy:

• Google Preview: Science Experiments That Surprise and Delight: Dancing Raisins (pages 6-7)
• Google Preview: Science Experiments That Fizz and Bubble: Bubbling Blobs (Pages 16-17)

Science Experiment Idea: Try putting other small objects in soda to see if the bubbles will attach to them and help them float to the surface of the soda. Try a penny, a toothpick, a peanut, a skittle. Can you find something that the bubbles will float to the surface like the raisin?

Words to Know:
Density – How closely packed together the molecules of a substance are.
Bouyancy – Ability to float or rise to the top of a liquid or gas.
Float – To sit near the surface of a liquid or gas, to not sink.
Mass - How much matter fits in a given space.
Matter - Stuff
Weight - A measure of the force of gravity on an object. Materials with more density weigh more.
Volume – How much space a substance takes up.
*****The confusing relationship between weight and mass: On earth, a bowling ball can weigh about 10 pounds. If you take that same bowling ball to the moon it will weigh much less because the graviational pull of the moon is less than the gravitational pull on the earth. Weight is a measure of gravitational pull. So the weight of the bowling ball, or anything else, changes depending on where you weigh it. The mass of the bowling bowl does not change no matter where it is. The bowling ball has the same amount of mass  on earth as it does on the moon or anywhere else you take it.

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Every time an object moves on earth it is rubbing against something else; another object, the ground, a tabletop, etc. Whenever two objects rub against each other friction happens because objects are not slick. If you look at objects under a microscope they are actually very bumpy. When the microscopic bumps on objects rub together, friction happens and the object that is moving slows down and eventually stops.

Gravity holds objects on the earth and friction keeps objects from sliding all over the place. Zero gravity looks fun when astronauts get to float but zero gravity makes things hard too. What if everything floated? We would be chasing objects all the time. Now think about what life would be like if there was no friction. You could just slide along the sidewalk with no effort at all…but it would be really hard to steer and stop…kind of like roller blades. The wheels on roller blades help reduce your friction so that you can glide across the ground, but as you know, it is tricky to steer and stop.

Do you know you to shuffle playing cards? You divide the deck in half and then use your thumbs to make the cards alternate as they overlap. If you try to pull the two sides apart, it’s hard – because of friction. All of the cards are rubbing together. However, if you make a bridge, the cards easily fall back into place in one pile. When you make the bridge the cards bend so that less surface area of the cards is touching each other. Less touching=less friction.

 

What You Need:

• 2 Thick Books

Today’s experiment will show you just how influential friction can be. Phone books works great for this but any two thick books will do. Place the two books on a table. Push them apart – they slide across the table easily. However, if you overlap some of their pages…it’s not NEARLY as easy.

Open two books and overlap each page of the two books. About half of the page of one book is laying on top of about half of the page of the other book – like your are shuffling playing cards.  Now try to pull the two books apart. Can you?

This video will show you just how much strength it takes to pull two phone books apart. Friction is no small force!

Here is a game you can play to figure out how friction affects moving objects:

Here are some websites that will help you understand friction:

•  The Guardian: Phone Book Friction Factor
• Physics4Kids: Friction

Here are some books that will help you understand friction and give you some more friction experiment ideas.

• Gizmos and Gadgets Chapter “Get a Grip” about Friction (Pages 28-48).
• Mythbusters Science Fair Book – Is It Possible to Pull Apart Two Phone Books That Are Laid Down With Alternating Pages? (Pages 110-111)

Words to Know:

Friction -

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What You Need:

 

 

• Ziploc Bag
• Water
• Several Sharpened Pencils

Fill the ziploc bag half full of water. Zip it closed. Hold a pencil in one hand while you use the other hand to poke the pencil all the way through the ziploc bag – have the pencil go in one side and come all the way out the other side. Repeat with more pencils.  Does any water spill out? Do you know why? No water spills out the holes because ziploc bags are made of a polymer.

Polymers have long chains of molecules that are flexible. When you poke the sharp pencil into the plastic the pencil point slides in between the chain of molecules that make up the polymer. The molecule chains ”hug” the pencil, making a seal around the pencil that won’t let the water out. What happens when you pull the pencils out?

Once you figure out how to do this one, try to get someone to stand still while you are holding the bag over their head. Poke the pencils through the bag to get them to trust your science…then pull the pencils out and see what happens! We tried it over the dog’s head. She liked it when the pencils got pulled out – a dog drinking fountain!

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

• Steve Spangler Science: Skewer Through a Balloon
• Cool Science Skewer Through a Balloon
• Science Squad Balloon Kebab
• Science Rocks! Slime Time (page 26)
• Naked Eggs and Flying Potatoes The Leakproof Bag (pages 128-131)

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.
Polymers – Molecules arranged in a long chain.

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Have you ever put a coin in one of those wishing wells that is shaped like a giant funnel? The coin rolls around and around the sides of the funnel in smaller and smaller circles until it goes down the hole in the middle of the well? That coin is demonstrating centripetal force. Centripetal force is the force that pulls a thing toward the center of rotation….like the little whirlpool that forms when you drain the bathtub or like the Zinga at Holiday World! Why IS that water slide called Zinga? Because in Swahili Zinga means “to move in a circular motion”. Lots of amusement park rides work because of the laws of physics.

You can use a balloon to demonstrate centripetal force.

What You Need:

• Balloon
• Hex Nut

Blow up a large balloon. Before you close the balloon, put a hex nut in it and then tie the end of the balloon closed. Hold the balloon between your hands and move it in a circular motion until the hex nut starts to roll around the inside of the balloon. Now stop moving the balloon and watch what happens to the hex nut. What you are seeing is centripetal force. The hex nut is on a circular path inside the balloon. Things that are moving in a curved or circular motion will slowly move toward the center of the circle, in this case, the bottom of the balloon. What sound does the hex nut make? How about a penny? A marble? Try them all and see how they behave the same or differently.

Here are some websites that will help you look at centripedal force and other physics laws that make amusement park rides work the way they do:

• Steve Spangler Science: Screaming Balloons
• PBS Kids: Fetch Whaohler Coaster
• Funderstanding Roller Coaster Demonstration
• Roller Coaster Physics: Design a Roller Coaster

Here are some books that will help you demonstrate Centripedal force and learn more about it:

• Google Preview: Naked Eggs and Flying Potatoes: Screaming Balloon(Pages 136-139)
• Google Preview: Super Simple Things to Do With Balloons: Let’s Go Nuts! (pages 10-11)

Words to Know:

Centripetal Force – A force that makes an object move in a  circular path toward the center around which the object is moving. It is the force that pulls a thing toward the center of rotation.

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Today’s project has three great elements, it’s easy, it’s fun and it’s a big mess!

 

What You Need:

• Cornstarch
• Water
• Bowl
• Measuring Cup
• Cookie Sheet or Tray – with sides!
• Gallon Size Ziploc Bag (optional – for storage)

Put 1 cup of cornstarch in a mixing bowl. Add water slowly to the cornstarch – about 1/2 cup. Mix the cornstarch and water with your hands until it starts to feel like a sticky glue.  Try to pick up a handful of the goo. Squeeze your hand around the goo to make a fist around it. What happens? Now relax your hand. What happens now? Pour the goo onto a cookie sheet or tray. Make sure the sheet or tray has sides! Lay your hand on top of the goo and leave it there for a few seconds. Pull your hand straight up and watch what happens.

Cornstarch goo is an anomaly – that means it’s weird! It doesn’t act like it should. Sir Isaac Newton is famous for figuring out certain rules that apply to things on earth. One of his rules is that matter can take three forms: solid, liquid and gas. Liquids flow and take the shape of the container they are in. The cornstarch goo seems like a liquid because it flows off your fingers and it takes the shape of the container you put it in. But when you squeeze the goo…it turns into a solid. So which is it? A liquid or a solid? Cornstarch goo is called a non-Newtonian fluid because it doesn’t behave by Sir Isaac Newton’s rules.

Cornstarch goo is also a polymer. That means it’s molecules are arranged in a long chain. When the chain of molecules stretches…like the goo flowing off the fingers in this photo, the goo behaves like a liquid and flows. As soon as the goo has pressure applied to it – like when you squeeze it in your fist or when you rest your hand on it in the tray, it behaves like a solid and feels stiff and strong.

Usually matter turns into a liquid when it is heated and when liquid is heated it “gets runnier.” How easily a liquid flows is called viscosity. Water has a low viscosity and flows fast. Honey has a high viscosity and flows slowly. If you heat honey or lava…it flows faster. That is one of Sir Isaac’s rules too…that the viscosity of liquids goes up as the liquid is heated. With cornstarch goo, the viscosity changes when you put pressure on it instead of when you heat it. Weird again!

Science Project Idea: Get three bowls and measure 1 cup of a powdered substance into each bowl. 1 cup of cornstarch in bowl #1, 1 cup of baking soda in bowl #2 and 1 cup of flour in bowl #3. If you step back and look at the bowls they will all look pretty much the same – a bowl with white powder in it. Now pour 1/2 cup of water into each bowl and mix each bowl with your fingers. Do the mixtures behave the same? How do they behave differently? How would you describe each mixture? A solid or a liquid? You could also try baking soda and powdered sugar.

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

• Exploratorium: Outrageous Ooze
• Science Bob: How to Make Slime
• The Museum of Science and Industry: Make Slime
• Steve Spangler Science: Non-Newtonian Cornstarch Recipe
• Instructibles: How to Make a Non-Newtonian Fluid
• WiseGeek: What is a Non-Newtonian Fluid?
• Science Rocks!: Slime Time (page 26)
• Naked Eggs and Flying Potatoes: Cornstarch Science – Quicksand Goo (pages 104-109)

Words to Know:

Polymers – Molecules arranged in a long chain.
Non-Newtonian Fluid – A fluid that doesn’t flow like you would expect when you put pressure on it.
Liquid – A state of matter. In the liquid state, matter can flow or take the shape of the container it is in.
Viscosity – How resistant to flowing a liquid is. Water has low viscosity and flows fast. Honey has high viscosity and flows slow.

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