Here's why:
* Forces are pushes or pulls. They can change an object's motion, shape, or direction.
* Balanced forces cancel each other out. If you push a box with equal force in opposite directions, the box won't move.
* Unbalanced forces cause a change in motion. If you push a box harder in one direction than the other, the box will move.
Examples of unbalanced forces that set objects in motion:
* A person kicking a soccer ball: The kick applies a force that makes the ball move.
* A car accelerating: The engine's force overcomes friction and makes the car move faster.
* Gravity pulling an apple from a tree: Gravity is an unbalanced force that causes the apple to fall.
In summary, an unbalanced force is the driving force behind an object's motion.
