Eli5 Why is force equal to mass multiplied by acceleration and not speed ?

Question

If a car moves consistently at 80 kmh and it weighs at 600kg, is it not generating any force? since you know, a=0, am I stupid or is Newton ?

In: 13

Answer 1

For the car, it has to constantly push against the air so it needs force just to keep at the same speed (the air is applying the same force back against the car).

So let’s imagine things in space instead:

If you push a rock floating in space it will speed up. If you stop pushing on the rock it will keep going at the same speed even though you’re not applying any force to it.

It still has energy from its speed of course, and if hits something it converts that speed into a force on the other object.