You know your car has gears, and that those gears are often talked about in terms of ratios they share with one another. But what do those gears do and by what dimensions are they being compared? Here’s an article to introduce the basics of the gears in your transmission (and the gears in all kinds of things) so you can wrap your head around it a little easier.

Anything with spinning parts is going to have gears. Car engines and transmissions have gears, blenders have gears, hair dryers have gears, coffee grinders have gears, fans have gears, VCRs have gears, clocks have gears… they’re everywhere. And it’s because they’re really useful. Here are the four tasks they typically perform:

  1. They reverse the direction of a rotation.
  2. They increase or decrease the speed of rotation.
  3. They move rotational motion to a different axis.
  4. They keep the rotation of two axis synchronized.

gear2If two gears are rotating in opposite directions and the smaller gear is spinning twice as fast as the larger gear and the axis of rotation of the smaller gar is to the right of the axis of rotation for the larger gear, the fact that the smaller gear is spinning twice as fast as the other has to do with the ratio between the gears, or the gear ratio. Now you know what people are talking about a little more, and maybe why.

If the diameter of a leftmost gear is twice that of a rightmost gear, their ration is 2:1 i.e. every time the large gear completes a full rotation, the smaller gear has completed two full rotations.

Another thing worth knowing about gears: most of them have teeth. Teeth prevent the slippage between gears that are supposed to work systematically together, they make it possible to determine exact gear ratios (all you have to do is count the number of teeth in the two gears and then divide; one gear has 40 teeth and one has 20? 2:1 ratio), and they make it so that imperfections in the diameter and circumference of the two gears don’t matter up to a certain extent. This is because the gear ratio is first and foremost controlled by the number of teeth that each gear has, even if the diameters are slightly off.

gear3Now we’re ready to talk about gear trains. These are interlocking gears used to create large gear ratios. Say you start out with one gear that’s turning at 100 rpm, and it locks into another gear that is one fifth the size of the gear before. That means that the smaller gear will then turn at a rate of 500 rpm. If you attach that to another gear one fifth of the 500 rpm gear’s size, that smallest gear will spin at a rate of 2500 rpm. That’s how you work your way up to quick movements without having to use the kind of power that would spin the original gear at 2500 rpm. Indeed, gears truly make the world go round… or at least the wheels in our inventions.