# Why do headphones get tangled?

## The science behind those knots and what you can do to put a stop to them. By Roger Rassool.

How many times have you reached for the headphones in your backpack or drawer only to find the whole thing has become a pit of tangled snakes? Even if you packed them really carefully they somehow seem to form deep, intricate relationships with any other wires or cables close by. Coiling them up before putting them in only seems to make things worse.

This has just happened to me, again, and lacking the patience to undo the mass of knots gets me thinking. Why is it so? For once, I’m going to avoid calling on Newton and friends for an explanation. This is all about friction and knots – more the specialist subject of sailors.

First, consider a length of string held at each end. Stretch it out and visualise how nice it looks. Now, try and knot it without letting go of either end. OK, this seems quite hard if not impossible. Tying a knot always involves pulling one end through a loop. To do this, you always have to let go one end of the string. It’s the same with your headphones. You may coil them up ever so carefully, but as soon as you place them in your backpack, the ends are free.

And how they tangle, with maddeningly complicated knots that surely must be the work of a mischievous pixie. What else could pull the ends of your cable so precisely through loop after loop? Friction, actually.

No lead is perfectly smooth, so the cable gets jostled about when it comes in contact with another moving object, like other parts of the lead or even the surface of the backpack or drawer. Any movement of the lead or its surroundings provides the force to twist and form loops in the cable, and then to push one of the ends through the loop. Gravity helps too. It’s as simple as that.

I see you shaking your head and dismissing my explanation as woefully unequal to the matted tangles you’ve experienced. But before you dive in to search for that pixie, perhaps mathematical logic will help. Consider the fact that there is only one way of arranging the string in an un-knotted fashion, and an infinite number of possible knots. The likelihood of knots increases as the lead gets longer or the number of leads increases.

But there are tricks to avoid tangles. One way is to buy headphones with much shorter cables. Another solution is to carry them carefully coiled and snugged up in a small pouch which will reduce contact with other objects in your bag. And the latest variety of flat, fettuccine-shaped cables are less tangle-prone than the traditional round, spaghetti-shaped ones, because they can’t rotate in your bag to form loops so easily.

Musicians and sound engineers have a special method of winding cables, widely known as the “under/over method”. These cable-coiling professionals exploit the fact that, because of the way the metal inside a cable gets wound during manufacture, cables want to coil up a certain way. Working with this natural coil, there is much less twisting as each alternate loop undoes any twisting from the previous one. Next time you use the cable, you’ll find you can just pull one end away, and it will unwind without twisting and knotting. Several pros have shared the technique on YouTube, so amateurs can coil their cables this way too.

But I think the best and most common sense approach is to take a tip from sailors, who always keep their ropes tied in a coil. This can be as simple as using a trusty bread tie to keep your headphones coiled (they probably came tied that way when new) or using another piece of string for longer leads. Why does this work? Sailors are knot experts – they know you can’t tie a knot without letting go of one of the ends. That’s why they keep their ends secure. Try it for yourself.

Roger Rassool is a particle physicist at the University of Melbourne. His outreach programs have switched on a new generation to the wonders of physics.
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