Animations demonstrating the equivalence principle:

Scroll down to see all four animations.

Accelerating Elevator

An observer in an accelerating elevator in the absence of a gravitational field (left side) observes the same physical laws as an observer in a stationary elevator in the presence of a gravitational field (right side)

Accelerating Elevator - 2

An observer in an accelerating elevator in the absence of a gravitational field (left side) observes the same physical laws as an observer in a stationary elevator in the presence of a gravitational field (right side). The gray line (left side) follows the path of the ball viewed from an inertial frame.

Elevator in Freefall

An observer in an elevator in freefall in the presence of a gravitational field (left side) observes the same physical laws as an observer in an inertial frame in the absence of a gravitational field (right side). The gray line follows the path of the ball in the Earth frame (left) and the elevator frame (right).

Merry-go-round: A rotating coordinate system (This animation doesn't really demonstrate the equivalence principle)

A person (blue disk) throws a ball (black dot) from the side of a merry-go-round as it spins. The left side shows the path of the ball as viewed from an inertial frame, while the right side shows the path as viewed from the rotating merry-go-round frame.