A simple machine is a device that changes the direction or magnitude of a force. They can be described as the simplest mechanisms that provide leverage Figure 4. Usually the term simple machine is referring to one of the six classical simple machines, defined by Renaissance scientists.
Simple machines are devices used to multiply or augment a force that we apply—often at the expense of a distance through which we apply the force. Some common examples include:
- Wheel and Axle
- Inclined Plane
When a device with a specific movement, called a mechanism, is joined with others to form a machine, these machines can be broken down into elementary movements. For example, a bicycle is a mechanism made up of wheels, levers, and pulleys. Figure 3 shows a table of various simple machines.
A simple machine has an applied force that works against a load force. If there are no friction losses, the work done on the load is equal to the work done by the applied force. This allows an increase in the output force at the cost of a proportional decrease in distance moved by the load. The ratio of the output force to the input force is the mechanical advantage of the machine. If the machine does not absorb energy, its mechanical advantage can be calculated from the machines geometry. The mechanical advantage of a lever, shown in Figure 1, is equal to the ratio of its level arms. Simple machines which do not experience friction loss is called an ideal machine. For these ideal machines, the power (rate of energy) in equals the power out:
Wheelbarrows and shovels are also examples of simple machines (these utilize levers). They use only three forces: the input force, output force, and force on the pivot. In the case of wheelbarrows, the output force is between the pivot (wheel's axle) and the input force. In the shovel, the input force is between the pivot and the load (refer to Figure 2).