Here's why:
* Inertia: An object at rest tends to stay at rest, and an object in motion tends to stay in motion at a constant velocity (speed and direction), unless acted upon by an unbalanced force.
* Force: A force is a push or pull that can change an object's motion. To start moving, an object needs a force to overcome its inertia.
Examples:
* Pushing a box: You need to apply a force (push) to get the box moving.
* A ball sitting still: It will remain still unless you kick it (apply a force).
* A car parked on a hill: It will only start rolling downhill if gravity (a force) acts upon it.
In summary: For an object at rest to begin moving, there must be a net force acting on it.