Here's why:
* Newton's First Law of Motion: An object at rest will stay at rest, and an object in motion will stay in motion at a constant velocity (speed and direction) unless acted upon by a net force.
* Friction: In the real world, friction is a force that opposes motion. This is why it seems like we need a force to keep things moving. We need to apply a force to overcome friction and maintain a constant velocity.
Example:
Imagine pushing a box across a smooth floor. Once you get the box moving, you can stop pushing, and it will continue moving (albeit slowing down due to friction) in the same direction. If there were no friction, the box would keep moving forever at the same speed and direction.
Conclusion:
A force is required to *change* the motion of an object (start it, stop it, or change its direction), but not to *maintain* its motion in a given direction.
