30. Local Inertial Frame - Einstein's elevator

See Local Inertial Frame (Gravitational Acceleration). This demonstration is equivalent to the Monkey and Hunter example. A large aluminum frame is cranked up and suspended by a magnet. Two guns on one side of the frame are aimed in straight lines through holes in an intermediate Plexiglas sheet at target pockets on the other side of the frame. If the guns are fired while the frame is suspended, the projectiles travel in parabolas and bounce back from the plastic sheet. But now the guns are reloaded and frame is released to fall. Another switch fires the guns as the cage goes into free fall. When the falling frame is stopped by a "linear decelerator" (a shock absorber) at the bottom, it will be found that the projectiles reached the pockets. In the falling frame, they traveled in straight lines, obeying Newton's First Law.

Our device was designed by Dr. R.E. Berg of the University of Maryland (A.J.P. 48, 310 (1980)), and built by the UCLA physics machine shop.