Here's why:
* Work is defined as the product of force and displacement in the direction of the force.
* If a force is applied at an angle to the displacement, only the component of the force that acts along the displacement direction contributes to the work done.
* The perpendicular component of the force does not contribute to the work.
Example:
Imagine pushing a box across a floor. You push with a force at an angle to the floor.
* The component of the force parallel to the floor does work, as it causes the box to move horizontally.
* The component of the force perpendicular to the floor does no work, as it doesn't contribute to the box's displacement.
In summary:
* Work is done only by the component of the force that is parallel to the displacement.
* The perpendicular component of the force does not contribute to the work.
