Swinging Bob
I was introducing general relativity to my class yesterday and wanted to show some examples of how different experiments would be in both g field and accelerated frames of reference, so I made this pendulum in interactive physics. There is no gravity but there is a force applied to the rectangle which is accelerating upwards. The whole thing is viewed in the frame of reference of the rectangle (hence the evil eye). Shows nicely how even though there is only one force acting on the bob the pendulum swings.