Question

According to Newton's 1st law of motion, what is required to make an object slow down?

Answer 1

Hello,


 that there must be a cause—which is a net external force—for there to be any change in velocity, either a change in magnitude or direction.

So your answer is Force.

Force is required


Hope this helps

Answer 2

Newton’s first law state that an object in motion stays in motion unless acted upon force so the answer would be RESISTANCE