Newton’s Second Law of Motion

Written by tutor R Bruce N.

Newton defined one of the most important physics relationships ever.

He found that when an external force acts on an object, then that object accelerates – and the rate of acceleration is proportional to the mass of the object.


If the force is in line with current motion then the object goes faster.

If the force is in the opposite direction, then the object slows down.

Zero external force means no acceleration. That could mean constant velocity or it stays at rest.

It’s obvious, isn’t it? If you try to push a toy car, it’s easy and it accelerates a lot.

External forces - Newton's 2nd Law

Oops, it’s heavy!? NO Sweat!! I’m a big guy -I can handle this!

Try the same with a real car – much more mass and it’s harder to get it going.

External forces - Newton's 2nd Law

Anybody got a buck for gas?

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