Atwood's machine is the name of a device that looks like this: Also known as "two masses on a pulley". Surprisingly, this simple device comes up a lot in intro physics texts. It also brings up some ...

This is a classic introductory physics problem. Basically, you have a cart on a frictionless track (call this m 1) with a string that runs over a pulley to another mass hanging below (call this m 2).

Two masses pull a scale in different directions to measure the tension in the string. One mass can be detached and the string held in hand to simulate the string being attached to a wall. The string ...