Here's why:

* Force: A force is a push or pull that can change an object's motion.

* Unbalanced Forces: When the forces acting on an object are not equal in magnitude and opposite in direction, they are considered unbalanced.

* Acceleration: Acceleration is the rate of change of velocity over time. This means an object is accelerating if it's speeding up, slowing down, or changing direction.

In simpler terms: When you push a box across the floor, you are applying an unbalanced force. This force causes the box to start moving (speed up) and continue moving until another force (like friction) balances it out.

Let me know if you'd like more examples!