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# How does a Zipper Work?

## What is Zipper?

A zip is a wonderful modern invention that makes your life extremely convenient. Think of how much time it takes to button up a shirt versus the time it takes to zip up a jacket. Zippers are very convenient and can be made from almost any material. They come in different shapes and sizes and ever since they were invented by Gideon Sundback in 1917 they have become an integral part of jackets, pants, suitcases, sleeping bags, shoes… well, you get the idea.

The function of a zip relies on two basic principles- the wedge and the hook.

The wedge is a simple machine. It is any triangular shaped object that can be used to exert force perpendicular to it. Think of that cabinet in your kitchen that never remains shut. If you push a wedge between the door of the cabinet and the frame, it will exert pressure sideways on the door and the frame at the same time, keeping it shut.

The second principle is the hook. A simple curvy shape that allow you to grab on to something.

### ZIP ME UP

The zipper is made up of 2 main parts: a slide which you use to open and close the zip and a set of teeth that are on either side the object you want to zip up.

If you look carefully at the teeth you will notice that each tooth is exactly the same distance away from the next and each one of them are identical. This is absolutely necessary for a zip to function properly.

The design of the tooth on this track is such that they are able to interlock with each because it is shaped like a hook. With the help of the slide each tooth can hook onto the one above and below it. The slide allows each hook to meet at a particular angle that locks into position once its moved on. This is where the slide comes in.

When the slider is going in the other direction it once again angles the teeth so they can be released and a wedge in the slide physically pushes them apart. We learnt before that the force exerted by a wedge is always perpendicular to it, so even though the slide is going down it pushes the teeth of the zip sideways.

It really is that simple!

PROJECT
The Wedge is one of 6 simple machines. Find out what the other 5 are by typing in simple machines in the search bar.