21. Newton's first law of motion states that an object stays in constant motion unless a(n) force acts on it.

Outside

Explanation:

Newton's First Law of Motion states that a body at rest will remain at rest unless an outside force acts on it, and a body in motion at a constant velocity will remain in motion in a straight line unless acted upon by an outside force. ... Outside forces are sometimes called net forces or unbalanced forces.

wheres the answers ?

this transfer is call conjunction