Principles of Mechanical Devices

Mechanisms

All machines, however basic or complex, are made up of simple mechanisms. A mechanism is a device which changes an input motion and force, into a desired output motion and force.

As in electronic systems a simple mechanical systems diagram contains three stages:

  • Input: the input begins the system, such as the lever shown below for the car jack.
  • Process: this is the thinking or operating part of the system, which begins to raise the jack.
  • Output: this is the system's response which lifts the vehicle.

The car jack uses a screw and nut mechanism.

This changes the turning motion (or rotary motion) at the screw into a straight line motion (or linear motion) at the nut, and changes a small force at the screw into a large force at the nut.

In this way, only a small effort is required by the motorist, to raise the heavy load through the action of the scissor mechanism.

woven fabrics

Although designed to do different jobs, all mechanisms have some things in common:

  • They involve some kind of motion.
  • They involve some kind of force.
  • They make a job easier to do.
  • They need some kind of input to make them work.
  • They produce some kind of output.

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