Some machines can actually speed up a task. They do this by reducing the distance over which the effort is applied. Increasing the speed at which a task is performed requires more force than would otherwise be necessary. Some gears require more effort, but they make the bicycle travel faster on flat terrain. Other gears require less effort and are useful for climbing hills.
People use simple machines, such as levers and pulleys, to make manual chores easier.
The mechanical energy in a person's muscles makes the machine do work. Not all machines use muscle power, however, to do work. A complex machine, such as an airplane engine or an elevator, is made up of many simple machines. Airplane engines and elevators are not powered by hand. Complex machines often use the energy stored in chemical substances, such as airplane fuel or the energy stored in electricity, to provide the necessary force to do work.