So you’ve got a heavy load, and you want to move it. You might try a simple machine that’s the basis of much modern machinery — a pulley. There are six simple machines: an inclined plane, a lever, a screw, a wedge, a wheel and axle, and a pulley. Basically, a pulley changes the direction of an applied force. Thus, for instance, you can pull on the cable of the pulley, and it will pull a weight.

A pulley, which is derived from the Greek word polos, meaning axis, is a wheel with a groove. A rope, belt, or cable runs inside the groove. That mechanism can be used alone or connected with other pulleys in a pulley system. The greater the number of pulleys in the system, the less force it will take to lift an object.

A block and tackle system, which is a basic pulley system, can illustrate how pulleys provides this kind of lifting advantage. Consider this: you have a 10-pound weight with a rope attached to it. To lift it up, you’ll need to exert 10 pounds of force straight up. If you have it attached to one pulley, you’ll still need to exert 10 pounds of force, but the direction you’ll exert is down, instead of up, thus making use of your body weight more efficiently. If you have it attached to two pulleys, you’ll need to exert only 5 pounds of force. Four pulleys, 2.5 pounds of force, and so on.

There are three basic types of pulley systems: (1) fixed, with a fixed axle, (2) movable, with a free axle, and (3) compound, with a combination of fixed and movable axles. Movable and compound axles, by multiplying the force, are more efficient than fixed pulley systems.

Another type of pulley system is the belt and pulley system. You’ve probably seen one of these under the hood of your car. Belt and pulley systems are closed systems in which several pulleys are connected by one belt. They allow for the transmission and amplification of energy from one pulley to another.