Spring Has Sprung

With the arrival of the very summery weather and the Angry Birds still flying through my mind, it seems like there’s no better time to talk about springs. No, not the ones that follow winter, but the ones that help make life easier or more fun, from bungee jumping to the shock absorbers in cars, springs are important to a whole range of applications.

Let’s start by imagining one of those inflatable bungee runs that you see at fairgrounds, pitting two people against each other to see who can go the furthest before the spring pulls you back with a bang. If one person is a lot stronger or heavier than the other, it’s not really a contest, because it will be a lot easier for them to stretch the bungee than the smaller, weaker person. From this we can see that there is a relationship between the force F that someone can exert and how much the bungee stretches, which is also called the extension x.

But you know from experience that not all springs are the same, the one inside a pen is much smaller than the ones inside a car, and elastic bands, which are another type of spring, can be quite easy or quite hard to stretch depending on their size. What we need is some sort of number, that defines how hard it is to stretch something. It’s called the spring constant, and is given the letter k. So the full equation is

The last thing we need to look at is how to measure the extension, which is the change in length of the spring (actually how much you manage to stretch that bungee by).

Easy!