Name: edHelper Lever, Wheel and Axle, and Pulley

The lever, the wheel and axle, and the pulley are three simple machines that have something in common. It's easy to see how the wheel and axle and the pulley are related; a pulley looks a lot like a wheel and axle with a rope over it. But what about the lever? A lever doesn't look much like a wheel and axle or a pulley. For starters, it isn't even round! So you may be surprised to learn that the lever is the basic simple machine that the other two are based on.

A lever is a bar with a balance point called the fulcrum. A garden shovel is an example. In a wheel and axle, the fulcrum is in the center. The outside rim of the wheel is like the handle of a lever; it just wraps all the way around. A pulley is just what it looks like, a wheel and axle with a groove to hold a rope around the outside edge.

A lever helps you do more work than you could do by yourself. It seems like it makes you stronger, but it really doesn't. Like all simple machines, a lever can either give you more force or more distance, but as you get more of one you always give up some of the other. Levers are also used just to change the direction of a force.

There are three kinds of levers. A first class lever like a seesaw has the fulcrum in the middle. You push down on one end; this is called effort. The seesaw lifts up the kid on the other end; this is called the load. A second class lever has the fulcrum at one end, the load in the middle, and the effort at the far end. An example of a second class lever is the wheelbarrow you use when you work in your garden. A third class lever has the fulcrum at one end, the effort in the middle, and the load at the far end. A garden shovel is a third class lever. So are a broom and a baseball bat.

Before there were wheels with axles, there were simple wheels, or rollers, such as logs used to move a heavy object. With the slightly more modern wheel and axle, it is a little easier to see that it is a type of lever. The fulcrum, or axle, in the center can be turned to increase the distance at the outside edge. Examples of this are the wheels on your car, bike, or skateboard. A wheel can also be used in the opposite way to increase the force instead of the distance. For example, in old grain mills, a water wheel would be turned by flowing water to produce force to grind the grain in the mill. The handle on a doorknob or water faucet works the same way.

A simple pulley just changes the direction of a force, like the pulley that pulls up a bucket of water from an old well, or the pulley that helps you raise the flag on a flag pole. A block and tackle is a set of pulleys in two rows. It is used to lift heavy loads. In a block and tackle, a rope is wrapped back and forth over two rows of pulleys. For each pulley, you have to pull the rope a little further but you also gain a little more force. The giant cranes that you see on construction sites use a block and tackle, along with other types of machines, to do their job.

The lever, the wheel and axle, and the pulley -- three simple machines, or just three forms of the same machine? It all depends on how you look at it. Name: edHelper Lever, Wheel and Axle, and Pulley Questions

1. Name three simple machines. A. lever, crane, shovel B. wheel, axle, pulley C. lever, wheel and axle, computer D. lever, wheel and axle, pulley 2. Which best describes a block and tackle? It is a set of A. cranes B. wheels and axles C. levers D. pulleys 3. A door handle is an example of A. a pulley B. an inclined plane C. a lever D. a wheel and axle 4. The word fulcrum means A. a pulley rope B. a lever C. the balance point of a lever D. the axle in a wheel 5. A wheelbarrow is A. a third class lever B. a fourth class lever C. a second class lever D. a first class lever 6. This article is mainly about A. all simple machines B. three simple machines C. pulleys D. the lever 7. Simple machines can be used to A. neither B. both C. increase distance D. increase force 8. Can you name all six simple machines?