Originally aired during the week of January 12, 2009
What's a Gear? Take a wheel and axle system, add some teeth to the wheel, and you have a simple gear. When two gears are connected so that one turns the other, we say they are "meshed." So just what do gears do? Gears provide us with a mechanical advantage (the definition of any simple machine). Simply, the total amount of work done is defined by the amount of force applied for a certain distance. By using simple machines in combination with each other, we can create mechanical systems that give us the most efficient way to do work. To learn more about gears and how they work, register for the Vacation Day Science Special, Lego Madness at
www.montshire.org. Use gears and other Lego parts to create whimsical machines that move in surprising ways.
Gears are used in tons of mechanical devices. Eggbeaters, music boxes, cars, toys, drills, fishing poles, watches, bicycles, and the electric meter on your house or apartment all have gears, as does just about just about everything that has spinning. Gears are one way to transfer motion from one place to another. 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 mesh together at right angles such as bevel gears or crown gears, or go from a turning motion to a straight-line motion and vice-versa, such as with a rack and pinion. Spur gears transfer motion along a straight line. Learn more about gears Monday, January 19th at the Montshire during Lego Madness Science Special. Check
www.montshire.org for times and how to register.
Gears go together in groups of two or more. One gear turns another, which may turn another, and so on... The gear that turns the other one is called the "driver", and the gear being turned is called the "follower gear" or "secondary gear". 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. 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. Each time you turn the handle around once, the beaters rotate many times. To learn more about gears and how they work, register for the Vacation Day Science Special, Lego Madness at
www.montshire.org. Use gears and other Lego parts to create whimsical machines that move in surprising ways.
Imagine you are working on your chimney 30 feet above the ground and you need to get 60 pounds of mortar from the ground to the top of the chimney. You could place the mortar in a bucket and pull it up on a rope. You would need to exert 60 pounds of force for 30 feet to left the mortar to your position. But to make it easier, you use a block and tackle system with pulley to reduce the amount of force with which you will need to pull. This simple machine enables you to lift the mortar while exerting (or pulling) with only 20 pounds of force! Of course, you'll need to exert that force over a longer time - since there is still no free lunch in getting work done - but at least you won't break your back doing so! Like the block and tackle systems, we can create mechanical advantage with gear systems, enabling us to get a job done in the most efficient manner.
So what happens when you have a series of connecting gears? You have what is called a gear train. A gear train can be used to change the speed at which something rotates. Or, to put it another way, a gear train is a set or system of gears arranged to transfer rotational torque from one part of a mechanical system to another. The most important distinction in classifying gear trains is that between ordinary and epicyclic gear trains. In ordinary gear trains all axes remain stationary relative to the frame. But in epicyclic gear trains at least one axis moves relative to the frame. You can actually see and feel how a gear train works when you visit the Montshire Museum. Six different sized gears are attached to four axels. See and feel what happens when you turn the different hand wheels.
