Ch. 5 Work and Machines

Work

the transfer of energy that occurs when a force makes an object move

Work Equation

W = Fd

Power

the amount of work done in one second; it is the rate at which work is done

Power

the rate at which work is done

Power equation

P = W/t

Power equation for energy transfer

P = Et

Machine

a device that makes doing work easier

Some simple machines include

knives, scissors, and doorknobs

Some machines change the direction of the force you apply, like a car jack

you exert a force downward and the force exerted by the jack on the car is upward

Input force

the force that is applied to the machine

Output force

the force applied by the machine

Ideal (perfect) machine equation

Win=Wout

Efficiency

a measure of how much of the work put into a machine is changed into useful output work by the machine

Efficiency Equation

efficiency = Wout/Win×100%

Simple machine

a machine that does work with only one movement of the machine

Lever

a bar that is free to pivot or turn around a fixed point; the fixed point that the lever pivots around is called the fulcrum

Ideal mechanical advantage

IMA

IMA of a lever equation

IMA = LinLout IMA

Pulley

a grooved wheel with a rope, chain, or cable running along the groove

Wheel and axle

a simple machine consisting of a shaft or axle attached to the center of a larger wheel, so that the wheel and axle rotate together

The IMA of Wheel and Axle Equation

IMA = rw/ra

Inclined plane

a sloping surface that reduces the amount of force required to do work

IMA of an Inclined Plane Equation

IMA = l/h

Screw

an inclined plane wrapped in a spiral around a cylindrical post

Wedge

another type of simple machine where the inclined plane moves through an object or material

Compound machines

two or more simple machines that operate together