How do gears

If you want to, you can make a small turning handle on the big gear by taping a little piece of Styrofoam so it stands straight up on the gear. The big gear is the driver. Try turning it slowly. What happens to the little gear? Which way does it turn? Draw a big colorful dot on each gear, and position the gears so that both dots are at the top. As you turn the big gear, have one person count how many times the big gear turns all the way around and another person count how many times the small gear does.

Do they turn the same number of times? Gears work to change the direction of motion. When you turned the big gear one way, the little gear turned the other way! Gears also change speed of motion.

When you turn the big gear slowly, the smaller gear turns faster. An inclined plane, such as a ramp, is a kind of simple machine that helps do work. A screw, just like the ones from a hardware store, is also a simple machine! A screw is made from an inclined plane being wrapped around and around.

To see how this works, you will need notebook paper, and a pencil or marker. The long edge looks like an inclined plane, although the paper is too thin to do any real work. Starting from one of the short sides of the triangle, wrap the paper once around the pencil or marker, then start rolling until the whole piece of paper is wrapped around the maker.

Put a finger on the end of paper to keep it from unrolling, and carefully pick up the screw you have made. Do you see how the long edge of the triangle is now traveling around and up the marker? This is just like the inclined plane wrapped on a screw! Sometimes, many spur gears are used at once to create very large gear reductions. Spur gears are used in many devices that you can see all over HowStuffWorks, like the electric screwdriver , dancing monster , oscillating sprinkler , windup alarm clock , washing machine and clothes dryer.

But you won't find many in your car. This is because the spur gear can be really loud. Each time a gear tooth engages a tooth on the other gear, the teeth collide, and this impact makes a noise.

It also increases the stress on the gear teeth. The teeth on helical gears are cut at an angle to the face of the gear. When two teeth on a helical gear system engage, the contact starts at one end of the tooth and gradually spreads as the gears rotate, until the two teeth are in full engagement.

This gradual engagement makes helical gears operate much more smoothly and quietly than spur gears. For this reason, helical gears are used in almost all car transmissions. Because of the angle of the teeth on helical gears, they create a thrust load on the gear when they mesh.

Devices that use helical gears have bearings that can support this thrust load. One interesting thing about helical gears is that if the angles of the gear teeth are correct, they can be mounted on perpendicular shafts, adjusting the rotation angle by 90 degrees. Bevel gears are useful when the direction of a shaft's rotation needs to be changed. They are usually mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well.

The teeth on bevel gears can be straight , spiral or hypoid. Straight bevel gear teeth actually have the same problem as straight spur gear teeth -- as each tooth engages, it impacts the corresponding tooth all at once. Just as with spur gears, the solution to this problem is to curve the gear teeth. These spiral teeth engage just like helical teeth: the contact starts at one end of the gear and progressively spreads across the whole tooth.

On straight and spiral bevel gears, the shafts must be perpendicular to each other, but they must also be in the same plane. If you were to extend the two shafts past the gears, they would intersect. The hypoid gear , on the other hand, can engage with the axes in different planes. This feature is used in many car differentials. The ring gear of the differential and the input pinion gear are both hypoid. This allows the input pinion to be mounted lower than the axis of the ring gear.

Figure 7 shows the input pinion engaging the ring gear of the differential. Since the driveshaft of the car is connected to the input pinion, this also lowers the driveshaft. This means that the driveshaft doesn't intrude into the passenger compartment of the car as much, making more room for people and cargo. Worm gears are used when large gear reductions are needed. It is common for worm gears to have reductions of , and even up to or greater.

Many worm gears have an interesting property that no other gear set has: the worm can easily turn the gear, but the gear cannot turn the worm. This is because the angle on the worm is so shallow that when the gear tries to spin it, the friction between the gear and the worm holds the worm in place. This feature is useful for machines such as conveyor systems, in which the locking feature can act as a brake for the conveyor when the motor is not turning.

One other very interesting usage of worm gears is in the Torsen differential , which is used on some high-performance cars and trucks. The smaller gear turns four times in the time it takes the larger gear to turn once. This means the smaller wheel is four times easier to turn: turning the small wheel around once requires only a quarter of the force used to turn the large wheel around once.

The larger wheel has four times as many teeth as the smaller wheel. This means that every time the larger wheel turns once, the smaller one turns four times. It takes four times as much force to turn the large wheel around once as it does to turn the small wheel around once.

The teeth in both wheels are all the same size.