// physics › Newton's Laws
Use Newton's second law F = ma to solve for force, mass or acceleration.
F = m a
A mind behind this: Isaac Newton 1642–1727
If you push something, it speeds up. The harder you push, the faster it speeds up. And the heavier the thing is, the less it speeds up for the same push. In short: force = mass × acceleration, written F = m a.
Acceleration just means how quickly the speed is changing. A car going from still to fast very quickly has high acceleration. It is not the speed itself — it is how fast the speed is building up (or dropping).
Yes. Push a 3 kg toy car so it accelerates at 4 m/s2 (its speed grows by 4 metres per second, every second). Force = mass × acceleration = 3 × 4 = 12. So you needed 12 newtons of push. A newton (N) is just the unit for force.
Just rearrange the same formula. To get mass, divide force by acceleration. To get acceleration, divide force by mass. Pick what you want in the 'Solve for' box and the calculator does the rearranging for you.
Because the push has to share itself out over more mass. Kick a football and it flies; kick a bowling ball the same way and it barely moves and your foot hurts. Same force, much more mass, so much less acceleration.
The second law contains the first one. If the force is zero, then acceleration is zero too — meaning the speed does not change. That is exactly what the first law says: no force, no change in motion.