What you need:
- 1 piece of firewood or another heavy object
- 3 pieces of kite string
- A sturdy hook or bar to hang the log from
What you do:
- Tie two identical pieces of kite string to the center of the log or heavy object.
- Hang the log up by one string and take the other in your hand.
- First, pull down slowly on the lower string. The upper string will break.
- Retie the strings and try again, but yank the top string quickly instead, and the bottom string breaks. Magic, right?
What happened?
Nope, no magic. It's science! Which string breaks depends how you pull. If you pull slowly, both strings will feel your pull, but the top string must bear the extra weight of the log, so the top string will break.
But if you yank down quickly on the bottom string, the log’s inertia keeps the it in place, so only the bottom string feels your pull, and it breaks first.
So that’s part of Newton’s First Law. Actually, Isaac Newton wasn’t even the one who discovered inertia. That was Galileo Galilei, a famous Italian scientist who lived about one hundred years before Newton did.
But there’s another part of this law that Newton did discover. Newton was the one who realized that moving objects resist change too – they want to keep moving at the same speed, in a straight line.
If you are in a car and you go around a corner, you may feel like you’re being “pulled” to one side. But in fact, the car is just turning and your body is still trying to move straight. If the driver suddenly brakes, the car will slow, but your body isn’t connected to the breaks, so you will feel like you are being “thrown” forward towards the windshield. In fact, you are still moving at the same speed, but the car has slowed down around you. This is why seat belts are so important!
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