The Pulley Machine
Two weights of varying masses are attached to the same string, separated by a frictionless disk.
With this setup, you can examine tension forces, potential energy and kinetic energy.
The pulley problem illustrates a correlation between a shared tension force and acceleration, seen through
$$F_{tension} = mg + ma$$
$$F_{tension} = Mg - Ma$$
$$\therefore a = \frac{g(m-M)}{m+M}$$
George Atwood
A system like this is called an Atwood's machine and was invented by George Atwood in 1784 as a laboratory experiment to verify the mechanical laws of motion with constant acceleration.