Gears are one way to transfer motion from one place to another. They work together in groups of two or more. One gear turns another, which may turn another, and so on... Gears are measured by counting the number of teeth they have. When used with an axle, gears are an example of the simple machine called the "wheel and axle". Gears can mesh together in many different ways to transfer motion. Gears can increase or decrease force, direction, torque or speed. The gear that is turning the other one is called the driver, and the gear being turned is called the follower. Driving a small gear by turning a larger gear is called gearing up, and driving a large gear with a small gear is called gearing down. The gear ratio can be written as:

Spur gears transfer motion along a straight line.

Bevel gears mesh together to transfer motion to right angles.

A rack and pinion, when used together, transfer rotational motion to linear motion and vice-versa.

Differentials are used in automotive mechanics to allow the power of the motor to be distributed between two wheels while allowing the wheels to turn at different speeds. This is useful when turning. The outside wheel turns at a faster speed than the inside wheel.

Cams are able to convert rotational motion into back-and-forth motion or simple motion into complex motion. Cams exist in many shapes (oval, elliptical, and scalloped-edged) and each causes a different kind of motion.

The worm gear and gear box are used to transfer motion at a 45 degree angle. When using the Legos, an axle is inserted into the worm gear. The worm gear can turn the spur gear, but the spur gear cannot turn the worm gear.

Chains are formed by snapping together numerous chain links into a loop. The main use of chains is to power gears with other gears that are not directly next to them. It should be kept in mind that while a driver gear meshed with follower gear turns the follower in the opposite direction of its own motion, a driver attached to a follower using a chain spins the follower in the same direction as its own motion.

Gear Division

One reason that Engineers use gears is that sometimes they want something to spin slower or faster. For example, engineers designed egg beaters to use a big gear next to two small gears to make the beaters spin faster. Every time you spin the handle around once, the beaters spin around many times. Now we are going to look at the LEGO gears and see how much faster/slower the gears actually go. If you put the yellow catch onto the axle, it is easy to count the number of times that the gears go around.

Student Worksheet for Division

Gear Multiplication

The next question to ask is "can I get any better than five times faster/slower?" Using the biggest and smallest gear meshed together there is a relationship of 5 to 1. Can I get any better than that? The first thing that people think of is of adding more gears in between the two gears. Eventually students begin to see that no matter how many gears are between - the relationship in the speeds is the same! This is why the gears in between the driver and the follower are called idlers.

What about putting more than one gear on the same axle? Sometimes students ask this on their own, sometimes not... The key is to think about multiplication. We know how to get a 5 to 1 ratio. If we want to get, say, a 25 to 1 ratio, we want to get one axle spinning 5 times faster than the first, and the next axle 5 times faster than that one! Woah... With three axles, and two gears of different sizes on the middle axle, it is possible to get better than a 5 to 1 ratio.

The idea that putting multiple gears on an axle has a multiplicative effect is not an easy concept to grasp. A good idea is to try to have students that understand it explain it to others, for there are many different ways in which to think about it. Here Jenny explains how her gear train of 25 to 1 works.