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.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: A 20 N object is placed on a surface and starts to slide. What is the most likely reason the object begins to move?
Possibilities:
- 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.