A comparison between a machine's output and its input. A machine's work output can never be larger than its work intake. Because of friction, a machine's work output is always less than its work intake. Mechanical efficiency indicates how much of the work input is turned into work output. As long as there is energy available from outside the machine, it will keep running and producing work.
Mechanical power is the product of force and velocity. For example, if a force of 10 newtons for one second would result in a power of 100 watts, then one watt would be enough to lift one newton per second. Energy is the capacity to do work; power is the rate at which work is done.
In reality, a machine will have some degree of efficiency, but here we will assume 100 percent for simplicity's sake.
Work is defined as the product of force and distance moved. For example, lifting a weight ten meters requires more work than lifting it one meter because you are working over a longer distance. In fact, one kilogram lifted ten meters uses the same amount of work as one kilogram lifted one meter because one kilometer is the same distance as one meter. It is important to understand that work is a measure of energy change; power is the measure of speed change. For example, raising a weight a hundred meters in an hour uses more power than raising it ten meters because you are raising the weight faster.
Because the machine must use some of the effort to overcome friction, a machine always accomplishes less work on an item than the user does on the machine. The percentage of effort put into a machine by the user (input work) that is converted into work done by the machine is known as efficiency (output work). For example, if a person pushes a rock up a hill using a wheelbarrow and then rolls it back down, the person has done only 20% of the work needed to move the rock up the hill. The rock will be slightly worn after being used for this task.
Efficiency varies between machines but is usually very low. A common example is a hand-powered drill. It requires much more effort from its user to drive the drill than it does to simply turn the handle. Other examples include electric drills and power mowers. They require less effort from their users to turn on than to push a button for them to start working.
In general, a machine can be thought as a tool that uses energy stored in a reservoir (such as a battery) to perform work. This work may be useful if enough energy is harvested in comparison to how much was stored in the reservoir. For example, it takes about 1 watt-hour (Wh) of electricity to lift one pound over your head. So if you had a battery that could produce 1,000 Wh of energy, you could lift 100 pounds without further input from outside sources.
A machine's efficiency is a measure of how efficiently it eliminates friction. It is determined as the percentage of input work that is converted into output work. The mechanical advantage of a machine is the number of times the input force is multiplied. For example, if a screw has a mechanical advantage of 3, then for every three turns of the handle you will get as much movement in the screw as there were turns on the handle. Therefore, the efficiency of a screw motor is 33%. Of the energy supplied to the motor, one third goes into driving the screw and two thirds is lost as heat.
The efficiency of a machine depends on many factors such as speed, size, load, type of drive mechanism, etc. Generally, the higher the speed, the lower the efficiency will be. Large machines are more efficient than small ones - this is because less effort is needed to produce a given amount of power at high speeds. If a machine is operating at a low speed, but producing a large amount of force, its efficiency is high even though it is losing some energy due to frictional forces.
Efficiency can also be defined as the output work divided by the input work. This definition does not take into account any potential losses within the system. For example, if a machine is working with 100% efficiency but loses 10% of its energy due to frictional forces, its actual efficiency would be 90%.
Machine Effectiveness The percentage of effort put into a machine by the user (input work) that is converted into work done by the machine is known as efficiency (output work). Because some of the input work is utilized to overcome friction, the output work is always less than the input work. As a result, efficiency is never 100 percent. For example, if 10 pounds of force are required to lift a one-pound weight one foot high, then the efficiency of lifting such a weight is 10/1, or 100%.
The amount by which efficiency can exceed 100 percent depends on how much friction there is in the system. If the resistance to movement is very low, more than 100 percent efficiency is possible. For example, if five pounds of force are needed to lift a two-pound weight one foot high, then the efficiency would be 200 percent.
In practice, however, it is difficult to achieve efficiencies higher than 100 percent due to limitations of human strength. Also, in many systems friction does not allow for high efficiencies. That is why most machines are inefficient compared with natural processes like humans. For example, a person can walk up steep hills without getting too tired because their body adapts to the stress caused by gravity, but most machines must be given time to rest before being used again because they consume energy even when they are idle!