Here's why:

* Work in physics is defined as the force applied to an object multiplied by the distance the object moves in the direction of the force.

* A motionless object, by definition, doesn't move.

Therefore, even if a force is acting on the object (like gravity on a book on a table), since there's no displacement, no work is being done.

Important Note: While the object may have potential energy due to its position, this is not the same as work. Potential energy is stored energy, not the energy used to perform work.