Newton's First Law — in 200 Words or Less

Reading my recent post about gravity the other day, it occurred to me that it might be fun to go back and do some basic science— in 200 words or less. Part exercise for me, part shot of science espresso for you. Today, Newton's first law.

It’s a humble but profound statement: objects in a state of uniform motion tend to remain in that state unless an external force acts on them. In plain English, Newton’s first law means that if you throw a baseball, it will go in a straight line at constant speed forever unless something pushes or pulls on it.

Of course, wind resistance and gravity are always pushing and pulling, so baseballs never go in straight lines at constant speed. To see the first law in action, find an ice rink or an air hockey table, and toss a puck along it. It’ll go straight at fairly constant speed for a while — longer, anyway, than a baseball would.

Why is the first law important? People once thought objects tended to stay motionless, so you had to push to keep them moving. They missed what’s obvious today: it’s friction that slows things down. Without friction, gravity, and other forces, things like hockey pucks and baseballs would keep moving forever.

Newton’s first law challenges us to think of all the forces involved, like friction and gravity. By doing that, it opens the door to a deeper, farther-reaching understanding of the physical world.