* Work is defined as the product of force and displacement in the direction of the force. Mathematically:

* Work (W) = Force (F) * Displacement (d) * cos(theta)

* Where theta is the angle between the force and displacement vectors.

* When force is perpendicular to motion: The angle between the force and displacement is 90 degrees. Since cos(90°) = 0, the work done becomes zero.

Example:

Imagine pushing a box horizontally across a frictionless floor. If you push straight down on the box (force perpendicular to motion), you won't move the box. No work is done because the force isn't causing any displacement in the direction of the force.