Category Archives: Science Experiments

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: The Tablecloth Trick and The Egg Drop. The two videos will give you good directions.

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?)
Giants of Science: Isaac Newton Isaac Newton and Physics for Kids Naked Eggs and Flying Potatoes Gizmos and Gadgets

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.

Card BridgeDo 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 bottomCard Shuffle 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 websites that will help you understand 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)
Gizmos and Gadgets Mythbusters Science Fair Book The Science of a Bicycle Friction and Gravity: Snowboarding Science

 

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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.

Easy Genius Weather Experiments

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

srphexnutFind More Science Experiments

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:

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

Naked Eggs and Flying Potatoes Super Simple Things to Do With Balloons Big Roller Coasters Speed and Acceleration

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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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:

srppendulum2

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:

Streg Nona: Her Story Many Ways to Move

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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