70. Local Inertial Frame - Einstein's Elevator


A coordinate frame in free fall in a gravitational field is truly inertial; that is, Newton's lst law is obeyed. In this demonstration a coordinate frame similar to that shown in the figure is held by an electromagnet. If the guns are fired while the frame is held, the projectiles will follow parabolic trajectories in the earth's frame and bounce off the intermediate plexiglass sheet. But if the frame is dropped, the guns firing automatically during the falling motion, the projectiles will follow straight lines in the falling frame and reach their target pockets.

Note that this demonstration is equivalent to the Monkey and Hunter demonstration.