Part 2: Ratios - Gearing Up and Down

Before we get started on Gear Ratios, we're going to do a quick review of the properties of gears. Do we remember what types of gears do what?

Now, onto ratios. When we talk about gear ratios, we're comparing the number of teeth, or the size, of one gear compared to the other gear. When we combine different-sized gears, we can change the energy being created by a motor, or as in this TigTag video, the energy created by our bodies.

Now for a couple of important terms:
  • Input Gear: The gear that is attached to a power source, like a motor or the pedals on a bicycle.
  • Output Gear: The gear that transmits power from the input gear, usually to a wheel or some other moving mechanism.
  • Gear Ratio: The number of rotations that one gear makes compared to another. Usually, we express the ratio of the larger gear, and write it like this: 2:1. This means that for every 2 rotations of the smaller gear, the larger gear will only turn once.
  • Gearing Up: When the output gear rotates faster than the input gear.
  • Gearing Down: When the input gear rotates faster than the output gear.
Next, Mr. Cyr will show you a few examples of gear trains, one that gears up, and one that gears down. You'll be discussing what you notice about each one.

Finally, you'll get some practice of your own in calculating gear trains. You'll be given the worksheet below, and you will need to figure out the gear ratios of each gear train presented, along with whether each gear train is gearing up or gearing down.