Lesson 4: Newton’s First Law: Keep Moving!
About 350 years ago, a scientist named Isaac Newton figured out three rules about forces and motion. The first rule is one you already know from experience, even if you did not know it had a name.
Newton’s First Law says: an object at rest will stay still unless a force acts on it. And a moving object will keep moving in a straight line unless a force acts on it.
This is why a golf ball on a tee does not move by itself — nothing is pushing it. And it is why a golf ball keeps flying through the air until gravity and friction bring it back to Earth.
Another name for this is inertia — the tendency of things to keep doing what they are already doing.
Newton’s First Law (Inertia): Objects at rest stay at rest. Objects in motion stay in motion in a straight line — unless a force acts on them.
Isaac Newton discovered his laws over 300 years ago. Can you think of another sport where Newton’s First Law is really obvious?
Inertia experiments: (1) Place a coin on cardboard on a table. Flick the cardboard quickly away — the coin stays! That is inertia. (2) Roll a golf ball and observe how long it travels before stopping — which forces eventually stop it? (3) Roll a golf ball and a tennis ball with the same push — which rolls farther and why? Record and explain each result using Newton’s First Law.
The coin-and-cardboard trick delights children every time. After the trick ask: ‘Which had more inertia — the cardboard or the coin? How do you know?’