Cranks have many uses and they can be found in some toys as part of a mechanism or in serious machinery such as car engines. Some cranks are attached to mechanisms that are difficult to turn or rotate.

 The diagram opposite shows the handle (crank) of an old fashioned record player, being turned. Turning the crank stores energy in a strong ‘spring mechanism’ inside the player. When the handle is released the stored energy in the spring turns the record, allowing music to play. Modern wind-up radios use the same type of mechanism.
Without the crank (handle) it would be very difficult or even impossible to wind the spring inside the player.

The crank acts like a lever, increasing mechanical advantage (the distance between the handle and the central shaft is increased - this makes it easier to turn).

Ed the Handyman winds the crank on his old fashioned record player. This stores energy inside the player.

Below is a good example of a crank shaft. When a shaft has two or more cranks it can be called a crank shaft. A typical example of a crank shaft can be found on small mechanical vehicles made for young children. As the child peddles the crank shaft rotates the wheels and the vehicle moves forward.

Above we see Ed the Handyman of Energy Efficient Cars. Ed thinks if he manufactures a full sized version of a child's crank shaft driven toy vehicle he can sell it to adults, helping them commute to work every morning. Would you buy one?

DISCLAIMER - Energy Efficient Cars is a fictitious company. Ed the Handyman is a fictitious character. Both have been created to support the article above relating to cranks