a balanced force is being applied. a frictional force is being exerted. an unbalanced force is being applied. a gravitational force is being exerted.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: If a book sitting on a flat table starts to move horizontally, it is most likely moving because
Possibilities:
- a balanced force is being applied.
- a frictional force is being exerted.
- an unbalanced force is being applied.
- a gravitational force is being exerted.

an unbalanced force is being applied.