Unit 5 - Work and Simple Machines (7th Grade Science)

STUDY
PLAY
work
the transfer of energy to an object by using a force that causes the object to move in the direction of the force (calculated by multiplying force by distance)
joule
the unit used to express energy (symbol, J); equivalent to the amount of work done by a force of 1 N (Newton) acting through a distance of 1 m (meter) in the direction of the force
machine
a device that helps do work by either overcoming a force or changing the direction of the applied force
work input
the work done on a machine; the product of the input force and the distance through which the force is exerted
work output
the work done by a machine; the product of the output force and the distance through which the force is extended
mechanical advantage
a number that tells how many times a machine multiplies force (calculated by dividing output force by input force)
mechanical efficiency
a quantity, usually expresses as a percentage, that measures the ratio of work output to work input (calculated by dividing work output by work input and multiplying the result by 100)
lever
a simple machine that consists of a bar that pivots at a fixed point called a fulcrum; used to apply a force to a load
pulley
a simple machine that consists of a grooved wheel over which a rope, chain, or wire passes
wheel and axle
a simple machine consisting of two circular objects of different sizes; the wheel is the larger of the two circular objects (its mechanical advantage is calculated by dividing the radius of the wheel by the radius of the axle)
inclined plane
a simple machine that is a straight, slanted surface, which facilitates the raising of loads; a ramp (its mechanical advantage is calculated by dividing its length by its height)
wedge
a simple machine that is made up of two inclined planes and that moves; often used for cutting (its mechanical advantage is calculated by dividing its length by its greatest thickness)
screw
a simple machine that consists of an inclined plane wrapped in a spiral around a cylinder (its mechanical advantage is calculated by dividing the length of its inclined plane by its height)
compound machine
a machine made of more than one simple machine
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