Simple machine

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Definition

A simple machine is a mechanical device that changes the direction and/or magnitude of a force, without supplying any energy of its own. Key features of a simple machine are:

  • A direction/point of application of the input force, which is called the effort
  • An output force, called a load, acting so as to move an object.

Classification of simple machines

The following concepts are used in the study of simple machines:

  • The mechanical advantage conferred by a simple machine is the ratio of load to effort. A mechanical advantage greater than 1 implies that a given effort can effect a greater load.
  • Simple machines can also be classified based on whether they alter the direction, i.e., whether the load and the effort are in the same or different directions.

The typical simple machines, and information on their mechanical advantage, are below:

Simple machine name Description Picture Computation of mechanical advantage Relationship between directions of effort and load Common examples
lever a rotating rod pivoted about a fixed point called its fulcrum. Fill this in later (Distance of effort from fulcrum)/(Distance of load from fulcrum) If effort and load are on the same side of fulcrum, the directions are the same. If effort and load are on opposite sides of the fulcrum, the directions are opposite. see-saws
inclined plane an incline, neither completely vertical nor completely horizontal. Taken here for simplicity to be a linear/planar incline Fill this in later 1 if used naively. However, it can be combined with other simple machines (like the pulley) to generate a mechanical advantage same
wheel and axle two coupled wheels (bigger one called a wheel, smaller one an axle) (Radius of wheel)/(Radius of axle) or (Radius of axle)/(Radius of wheel) depending on which of the two the effort is applied to. same (sort of. It's rotational motion, so "direction" should be interpreted accordingly)
pulley Fill this in later
wedge
screw