Here's the breakdown:
* Force causes acceleration: A force does *not* always change an object's motion directly. Instead, it causes acceleration, which is a change in the object's *velocity*. Velocity includes both speed and direction.
* Objects at rest can be acted upon by forces: Imagine a book sitting on a table. Gravity is acting on it, but the table's upward force balances it out. The book remains at rest, even though forces are acting on it.
* Forces can change direction without changing speed: Think of a ball in uniform circular motion. The force (towards the center) constantly changes the ball's direction, but its speed remains constant.
Therefore, while a force can definitely change an object's motion, it doesn't *always* do so. The key is to remember that a force causes acceleration, and acceleration can involve changes in speed, direction, or both.