Wheel and Axle The rotation of the against a point pries objects loose. That rotation motion can also do other kinds of work. Another kind of lever, the wheel and axle, moves objects across distances. The wheel, the round end, turns the axle, the cylindrical post, causing movement. On a wagon, for example, the bucket rests on top of the axle. As the wheel rotates the axle, the wagon moves. Now, place your pet dog in the bucket, and you can easily move him around the yard. On a truck, for example, the cargo hold rests on top of several axles. As the wheels rotate the axles, the truck moves. Pulley Instead of an axle, the could also rotate a rope or cord. This variation of the wheel and axle is the pulley. In a pulley, a cord wraps around a wheel. As the wheel rotates, the cord moves in either direction. Now, attach a hook to the cord, and you can use the wheel's rotation to raise and lower objects. On a flagpole, for example, a rope is attached to a pulley. On the rope, there are usually two hooks. The cord rotates around the pulley and lowers the hooks where you can attach the flag. Then, rotate the cord and the flag raises high on the pole. Screw Now, take an inclined plane and wrap it around a cylinder. Its sharp edge becomes another simple tool: the screw. Put a metal screw beside a ramp and it's kind of hard to see the similarities, but the screw is actually just another kind of inclined plane. Try this demonstration to help you visualize. How does the screw help you do work? Every turn of a metal screw helps you move a piece of metal through a Lever Try pulling a really stubborn weed out of the ground. You know a deep, persistent weed that seems to have taken over your flowerbed. Using just your bare hands, it might be difficult or even painful. With a tool, like a hand shovel, however, you should win the battle. Any tool that pries something loose is a lever. A lever is an arm that "pivots" (or turns) against a "fulcrum" (or point). Think of the claw end
We use the wheel and axle in gears. Gears have teeth around the outer rim. When the teeth of two gears fit together and one gear turns, it will cause the other gear to turn, but in the opposite direction. When the gears are the same size and they have the same number of teeth, they both turn at the same speed. If one gear is larger than the other, however, the smaller gear will turn faster. We use gears to regulate speed and direction of motion in complex machines and to increase/decrease the force applied. Machines that use gears include clocks, bicycles, cars, eggbeaters and other small household appliances. A crank is the handle of a machine that is connected at right angles to an axle. It is used to transmit motion. On a bicycle, the pedal attached to the gears is a crank. Cranks are used for turning, for example, the spinning wheel, eggbeater, peppermill etc. f) A Pulley Pulleys are wheels with grooves around the rim. The pulley turns as a string moves over the wheel and a load is raised as the string is pulled. This is a fixed pulley which doesn't change position. A fixed pulley makes work easier by changing the direction of the applied force. With a fixed pulley, the force required to lift the load remains the same as lifting it by hand, but realize how much easier it is to raise a flag or sail from the ground, as opposed to climbing up the pole or mast. If a force needs to be applied around a corner, a pulley allows us to overcome friction. With a moveable pulley, both the load and the pulley move; the load moves in the same direction as the applied force. Moveable pulleys allow you to use less force to raise an object than if you used only your hands. The amount of force required depends on the number of supporting ropes. The greater the number of pulleys and supporting ropes, the smaller the force required.