Many years ago, Sir Isaac Newton came up with some most excellent descriptions about motion. His First Law of Motion is as follows: “An object at rest stays at rest and an object in motion stays in motion unless acted upon by an outside force.” Quite a mouthful. What that means is that something that is sitting there will continue to sit there unless moved. And something moving will keep moving unless something stops it.
Still a mouthful. Just think about this: When you are at a stoplight in your car and you start moving quickly, you feel pushed back into your chair. The opposite is true if you come to a sudden stop, and you move keep moving forward, with only your seatbelt preventing you from crashing forward.
Here are a couple of experiments that demonstrate this very cool law of motion; in a word called “inertia.”
Ball Bounce Experiment
Materials for the Ball Bounce Experiment:
- A basketball or soccer ball, or similar bouncy ball
- a smaller bouncy ball (like a tennis ball or a racquet ball).
- Have an assortment of other balls handy for further experimenting.
Procedure:
- Do this experiment outside
- First bounce the basketball and tennis ball side by side to compare their bounces. Start them off around chest height
- Make a hypothesis (a guess) about what will happen when you stack the small ball on top of the bigger one and then drop it
- Try it! It may take a couple tries to line them up just right but the results are pretty awesome
Explanation:
The energy of motion from the bigger ball is transferred into the smaller one. Most of your attention is on the sky-rocketing smaller ball, but if you look at the basketball, it doesn’t have much bounce at all!
Experiment further:
Hopefully this will make you think of other things. Like what if you switched the two balls and dropped the smaller one on the bottom? What if you used two of the same sized ball? A golf ball on top? Think of other things!
Penny on a Card Experiment
Materials for the Penny on the Card Experiment:
- a small plastic cup,
- a playing card
- a coin.
Procedure:
- Put a playing card on top of the plastic cup
- Put a coin on top of the card
- With a sharp flick, hit the card out from under the coin! Or pull it really quickly toward you.
- The coin will drop into the cup.
Explanation:
The coin has inertia, meaning it really wants to stay in one place. If you move the card slowly, it isn’t fast enough to overcome that force. If you flick it quickly, the coin stays in one place and then drops into the cup. An object at rest will remain at rest. If you are brave, put the card on your finger and the coin on top… try to flick the card out until the coin stays on your finger. It can be done!
Experiment further:
Use a sheet of printer paper with a few heavier (non-breakable) objects on it. See if you can quickly pull the paper out from under the objects.
Another cool example of inertia: Put your hand, palm side up, next to your ear. Put a coin on your elbow. In one swift motion, bring your hand straight forward and try to catch the coin before it drops. If you’re fast (and lucky) enough, you will catch the coin before gravity has a chance to bring it down.
I hope you enjoyed this simple experiment and learned a little bit about the first law of motion and inertia. If you have more questions about this, or need tips about science fair ideas around this topic (or others), feel free to contact me.
Steve Davala is a middle school science teacher who likes to write. He’s got two kids of his own and subjects them to these science activities as guinea pigs. Follow him on Twitter or email him at steve.davala@gmail.com.
