Gravity exerts a balanced force on the object. An unbalanced force causes acceleration. Friction is applied to the object. The forces acting on the object are in equilibrium.
A 20 N object is placed on a surface and starts to slide. What is the most likely reason the object begins to move?

Options:
- Gravity exerts a balanced force on the object.
- An unbalanced force causes acceleration.
- Friction is applied to the object.
- The forces acting on the object are in equilibrium.

An unbalanced force causes acceleration.