Here's why:
* Newton's First Law: An object at rest stays at rest, and an object in motion stays in motion at a constant speed and direction *unless acted upon by an unbalanced force*.
* Newton's Second Law: The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. This means that *acceleration only happens when there is a net force*.
In simpler terms:
* If all the forces acting on an object cancel each other out, the object will either remain still or move at a constant speed in a straight line.
* If the forces are not balanced, the object will accelerate (change its speed or direction).
