Question

if an object is moving at a constant speed in one direction, what is needed to change its speed or direction?

Answer 1

a net force....at constant speed all the forces acting on the object is zero..

Answer 2

Newton's 2nd law basically says that an object accelerates when a net forces act on it.......and velocity is speed in a particular direction..........If a body accelerates, there is a change in velocity which means that either the speed or direction or speed and direction of the object changes.