Amazing Slinky physics

The Slinky is a simple toy, consisting of nothing more than a helical spring made of metal or plastic. Simple it may be, but don’t underestimate the scientific principles at play; you’ll learn a lot about a range of forces by playing with this toy. The best way to see these in action is to watch a Slinky as it tumbles down a flight of stairs.

Given a little nudge off the top step, the toy then independently falls from one step to the next in a fluid manner.
Within this seemingly straightforward descent, the Slinky demonstrates the effects of friction and inertia, potential and kinetic energy, the consequences of momentum and behaviour consistent with compression waves – the latter granting its distinct motion.

Inertia is the resistance of any physical object to a change in its state of motion or rest, such as the Slinky standing on its end, unmoved by any outside force.

This inertia is aided by the effects of friction, such as exerted on the spring by the Earth’s atmosphere, as well as between its own material and the surface on which the toy is lying (eg carpet).Despite inertia, however, objects have potential energy, which is the energy of an object granted by its position and particular makeup; a Slinky has potential energy due to its metal/plastic body, helical shape and position at the top of a flight of stairs, for example.

This potential energy is ‘released’ and converted to kinetic energy – the form of energy governed by motion – when acted on by an external force (in the case of the Slinky, this is when it is pushed over the top step).

Finally, moving objects possess momentum, which is the product of their combined mass and velocity. Objects with a larger momentum require more energy to move and to stop, while those with low mass and velocity have less momentum. As such, a metal Slinky is better at moving down stairs than plastic variants, as its greater momentum makes the toy more unbalanced between each step.