Most kids play with a slinky when they were little. That is until it gets tangled and twisted then it's no fun.When you push a slinky down the stair or a pile of books you created as a path, it requires energy to do so like everything else. But the energy required for this to work is elastic potential energy or the potential energy of a spring. PEs for short has the equation of (1/2)kx^2. As you push the slinky down the path the length of the slinky becomes the x value. The x value represents the compression or amount of stretch the spring has. Next you just need to find the k, or the constant, when isn't as clear. In most equations the k is given to you but if you have to find it you can use Hooke's law which is Fspring=kx. You would then use your given x and the force to solve for the k. The amount of force you use and the amount of stretch your slinky has can change your potential energy.