# Physics Chapter 4 Vocabulary 4.1 Work: the action that results when

```Physics Chapter 4 Vocabulary
4.1
Work: the action that results when a force causes an object to move in the direction of the
force; W = F x D
Joule: the unit used to express work and energy; equivalent to the newton-meter (N*m)
Power: the rate at which work is done; P = W/t
Watt: the unit used to express power; equivalent to joules per second (J/s)
4.2
machine: a device that helps make work easier by changing the size or direction (or both)
of a force.
Work input: the work done on a machine; the product of the input force and the distance
through which it is exerted.
Work output: the work done by machine; the product of the output force and the distance
through which it is exerted.
Mechanical advantage: a number that tells how many times a machine multiplies force;
can be calculated by dividing the output force by the input force.
Mechanical efficiency: a comparison expressed as a percentage of a machine’s work out
put with the work input; can be calculated by dividing work output by work input and then
multiplying by 100.
4.3
Lever: simple machine consisting of a bar that pivots at a fixed point, called a fulcrum;
there are three classes of levers based on where the input force, output force, and fulcrum
are placed in relation to the load.
Inclined plane: a simple machine that is a straight, slanted surface; a ramp
Wedge: a simple machine that is a double incliend plane that moves; a wedge is often used
for cutting.
Screw: a simple machine that is an inclined plane wrapped in a spiral.
Wheel and axle: a simple machine consisting of two circular ojects of different sizes; the
wheel is the larger of the two circular objects.
Pulley: a simple machine consisting of a grooved wheel that holds a rope or a cable; there
are two knds of pulleys—fixed and movable.
Compound machine: machine that is made of two ro more simple machines.
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