# Newton’s Third Law of Motion

Newton’s Third Law of Motion

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Newton’s Third Law of Motion: For every action there is an equal and opposite re-action.

SIMPLY: If you push an object, that object pushes back in the opposite direction equally hard.

In this video, an astronomer demonstrates Newton’s Third Law of Motion:

Gizmos and Gadgets – Action-Reaction Rocket (Pages 18-26)

 Here are some books that will help you do some reseach for your experiment if you are doing it for the science fair.

Words to Know:

Newton’s Third Law of Motion – For every action there is an equal and opposite re-action.

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# Inertia – Tablecloth Trick & Egg Drop

Inertia – Tablecloth Trick & Egg Drop

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Physicists study matter – all of the “stuff” in the universe and how that “stuff” moves. One of the most famous physicists of all time was Sir Isaac NewtonSir Isaac is most famous for explaining gravity, a concept we are so familiar with now it seems obvious to us. He is also famous for explaining how stuff moves, his Three Laws of Motion. Today we are going to look at Newton’s First Law of Motion called Inertia.

Newton’s First Law of Motion (Inertia): A still object will stay still unless a force pushes or pulls it. A moving object will stay moving unless a force pushes or pulls it.

Gravity and friction are forces that constantly push and pull the “stuff” on earth. So, when we roll a ball, it slowly comes to a stop. On the moon, where there is less gravity and friction, “stuff” floats, and keeps floating.

In this video, an astronomer demonstrates Inertia:

Here are some good websites that explain inertia or show you experiments to try:

You can try two Inertia Experiments at home:

For The Tablecloth Trick You Will Need:

Drinking Glasses (non-breakable!)
a Plate (non-breakable!)
a Piece of Frabric or Tablecloth with NO HEM
Water
a Table
The items on the tablecloth – the drinking glasses full of water and the plate – are not moving. According to Newton’s law they should stay still unless a force pushes or pulls them. When you pull the tablecloth out from under them friction is a force that causes the plate to move just a little, but since the cloth is slippery it pulls right out, leaving the plate and glasses full of water in place.

For The Egg Drop You Will Need:

Egg
Toilet Paper Tube
Pie Pan
Drinking Glass
Water

In The Egg Drop the egg is not in motion, it is at rest. According to Newton’s law it should stay that way. When you slap the pan away you apply force to the pan and it moves, knocking out the toilet paper tube also, but you did not hit the egg so it stays in place. It DOES drop though, since the support of the toilet paper tube is gone gravity acts on the egg and pulls it toward the earth.

In this video see how seat belts and head rests in cars help save lives by using Newton’s First Law of Motion (Inertia):

Here are some books that will help you understand inertia, learn about Sir Isaac Newton or get directions for inertia science experiments:

• Gizmos and Gadgets – Inertia Zoom Ball (pages 9-10); Inertia Coin Magic (page 12).
• Google Preview: Naked Eggs and Flying Potatoes: The Egg Drop  (Pages?)

Words to Know:

Physics – The study of matter and motion.
Physicist – A person who studies matter and motion.
Sir Isaac Newton – A physicist from the 16/17th Century who figured out gravity and three laws of motion.
Laws of Motion – Rules that explain how matter, or “stuff” moves on earth.
Inertia – Newton’s First Law of Motion. Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed upon it. SIMPLY: A still object will stay still unless a force pushes or pulls it. A moving object will stay moving unless a force pushes or pulls it.

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# Thick Book Friction

Thick Book Friction

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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 how to shuffle playing cards? You hold the card deck in one hand and then use your other hand to pull random numbers of cards off the bottom and put them on the top – an example is the blue card deck on the right. When you pull the cards up, it’s hard – because of friction. All of the cards are rubbing together. However, if you make a bridge, like the red card deck on the left, 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

This experiment will show you just how influential friction can be. Phone books work 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 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)

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# Centripetal Force – Tornado in a Bottle

Centripetal Force – Tornado in a Bottle

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A couple weeks ago we learned about centripetal force when we did the Hex Nut Balloon experiment. We learned that centripetal force is what makes an object move in a spiral pattern when it is travelling in a circle, like a penny in a funnel shaped wishing well. 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”.

Today, we are going to learn about how liquid and air behave when they are moving in spiral pattern. 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 forceWhat You Need:

• 2 Liter Soda Bottles
• Duct Tape
• Water
• Food Coloring (Optional)

The tornado in the bottle looks a lot like the water draining out of the bathtub. When liquids pour they make a spiral pattern around a center. This is called a vortex. Gravity is pulling the liquid down toward the hole while the force of the pouring water is rotating around a center point…the middle of the drain or the neck of the liter bottle.

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.

Vortex – Whirling liquid or gas, like a tornado or the water draining out of a bathtub.

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# Centripetal Force – Hex Nut Balloon

Centripetal Force – Hex Nut Balloon

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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 forceCentripetal 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: