Easy Inertia Experiment for Kids

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Have you seen the trick where the waiter would whip off the tablecloth without destroying the dishes or even a glass full of water? 

Nope, it’s not just something you see in movies. You can do it too in the comfort of your own home. But with young kids, the risk of broken plates is probably not worth the science lesson. Safety first!

Inertia Experiment 2 Story Tower

This simple inertia experiment demonstrates the science behind the tablecloth trick. It’s easy to set up and your kids will want to do it over and over again! 

Law of Inertia Experiment

Materials:

  • An object that is big enough to sit on top of a toilet paper roll but small enough to fit into the glass (we used a clementine and a tennis ball)
  • Glass cup
  • Index cards (you can also use a plastic plate or paper plate)
  • Toilet paper rolls

Instructions:

1. Place the glass cup on the ground or table.

2. Place the index card on top of the glass so that it covers the entire opening. 

3. Place the toilet paper roll on the index card, directly above the glass.

4. Carefully place the object on top of the toilet paper roll.

Inertia Experiment Setup

5. In one quick motion, pull the index card sideways off the glass. Make sure you don’t pull upward or downward, the index card should be directly parallel to the ground or table.

Inertia Experiment Index Card

6. Watch the object fall directly into the glass! (Sorry couldn’t get a clear picture)

Inertia Experiment Falling Fruit

If you dare, you can use an egg and drop the egg into the glass for added drama. I figured a clementine was a great size and weight and there was no need to waste a perfectly good egg. 

We tried using a tennis ball and the result was the same. The tennis ball was a little bigger than the clementine but it fell inside the glass without a problem. 

Inertia Experiment Tennis Ball

Science Behind the Fruit Drop Inertia Experiment

To understand the science behind this experiment, you have to first understand Isaac Newton’s First Law of Motion. It states that an object stays at rest or keeps moving at the same speed and in the same direction unless it is acted upon by an unbalanced force.

The toilet paper roll and index card are very light (low mass), they have very little inertia. Therefore, you can easily move them with little force. The friction from the index card was enough to move the toilet paper roll out of the way.

The clementine (or tennis ball or egg) is heavier (high mass) and require more force to move. Otherwise, according to the Law of Inertia, it will stay at rest. When the toilet paper roll moved out from underneath it, the force of gravity brought it down into the cup.

The best thing about this experiment is that there is a lot of room to explore. You can try it with different objects and even try building a higher tower and see if you can still get the object to drop in the glass. We went as high as 3 toilet paper rolls high and the clementine dropped into the glass as easily as when we only used 1 toilet paper roll. The only challenge is balancing the index cards and toilet paper rolls on the glass!

Inertia Experiment Fruit Tower
Inertia Experiment Fruit Drop

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