* Conservation of Angular Momentum: The washer's angular momentum (a measure of its rotational inertia) must be conserved. Angular momentum is calculated as:

* L = Iω

Where:

* L is angular momentum

* I is moment of inertia (depends on the object's mass and how it's distributed)

* ω is angular velocity (how fast the object rotates)

* Moment of Inertia Changes: When you shorten the string, you effectively decrease the moment of inertia of the washer. This is because the mass of the washer is now concentrated closer to the axis of rotation (your hand).

* Velocity Increases: Since angular momentum must remain constant, and the moment of inertia decreases, the angular velocity (ω) must increase to compensate. This means the washer spins faster.

In simpler terms:

Think of the washer as a spinning top. When you shorten the string, you essentially make the "top" smaller. Since the top has the same amount of "spin" stored in it, it has to spin faster to compensate for the smaller size.

Important Note: As the washer spins faster, its kinetic energy increases. This extra energy comes from the work you do in pulling the string shorter.