Boxi Learn › Physics › Stage 4 · Systems and Argument
A ball dropped on a moving train
PHY-5 Motion depends on who is watchingPHY-1 A force changes motion, it does not keep it goingX-3 Look from another side
What many people think
A ball dropped in a moving train lands behind you.
The idea
Sideways and downward motion are independent: the passenger sees the ball fall straight down, someone on the platform sees a parabola.
Explain it
A friend says a ball dropped in a fast train must fly to the back of the carriage. Use two views, the passenger's and the platform's, to explain where it lands, and say when it really would land behind.
Try at home
Walk at a steady pace and toss a soft ball straight up, a little above your head. It comes back down into your hand. Now toss it and stop suddenly: where does it come down?