In this topic you will learn how simple machines make work easier.

A machine is a device that makes it easier for us to do work. Machines can range from very basic to very complex. The most basic kinds are called simple machines. These machines have few, if any, moving parts.

Sometimes a simple machine changes the direction of a force we apply to something. Machines can also increase the strength of an applied force. The force you apply to a simple machine is called the effort force. The force against which the machine acts-like the resistance of a nail to being pulled-is called the resistance force. The force the machine applies to an object in response to our effort force is called the output force.

Levers are simple machines. A lever has a rigid bar that rests on a pivot point. The pivot point is called the fulcrum. The side of the bar on which a person applies an effort force is called the effort arm. The side of the bar on which the lever produces an output force is called the resistance arm.

For levers the positions of the fulcrum, effort force, and output force can be different. In a first-class lever, the fulcrum lies between the effort force and the output force. In a second-class lever, the output force is between the effort force and the fulcrum. In a third-class lever, the effort force is between the output force and the fulcrum.

All simple machines do work. If there is no friction, the work put into a machine must be the same as the work done by the machine. The work input for a lever equals the effort force times the distance the effort arm moves. Work output equals the output force times the distance the resistance arm is moved.

For any simple machine, there is a number. This number is called the mechanical advantage. It tells us how much the machine should multiply our effort. A machine's mechanical advantage is found by dividing the distance that the effort arm moves by the distance the resistance arm moves as the machine does work.

A pulley is a grooved wheel that turns by the action of a rope in the groove. A pulley system is made of several pulleys acting together. Single pulleys acting alone can be either fixed or movable. A system of fixed and movable pulleys is sometimes called a block and tackle.

A simple machine made of a handle or axis attached to the center of a wheel is called a wheel and axle. A wheel and axle often has a large mechanical advantage. Pedals of a bicycle act as a wheel, and the sprocket to which they are attached is like an axle.