Chapter 5 - Work and Machines

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Parker 8th grade


the product of force and distance when force is used to move an object


unit of work, the SI unit of energy


a device that changes the amount of force exerted or the direction in which force is exerted

input force

the force exerted on a machine

output force

the force applied by a machine

mechanical advantage

the number of times the force exerted on a machine is multiplied by the machine


the percentage of the input work that is converted to output work

actual mechanical advantage

the mechanical advantage that a machine provides in a real situation

ideal mechanical advantage

the mechanical advantage that a machine would have without friction

inclined plane

a simple machine consisting of a flat surface with one end higher than the other


a simple machine consisting of a device that is thick at one end and tapers to a thin edge at the other


a simple machine that consists of an inclined plane wrapped around a central cylinder to form a spiral


a simple machine consisting of a rigid object that pivots about a fixed point


the fixed point around which a lever pivots

wheel and axle

a simple machine consisting of two circular objects that are fastened together and rotate about a common axis


a simple machine consisting of a grooved wheel around which is wrapped a rope, chain, or cable

compound machine

a device that combines two or more simple machines


two or more wheels linked together by interlocking teeth

ideal machine

machine with no friction

Simple machines do not multiply energy

W(out) is never > W(in)

A watt is equal to __________

one newton per second


A transfer of energy when a force makes an object move in the same direction (Joules)


The rate or amount of work being done in one second (Watts)

mechanical advantage

how many times a machine multiplies a force


input compared to output

simple machine

machine that has only 1 movment

compound machine

combination of simple machines

The Force-Distance Trade-off

Machines often will increase the distance of the object has to move, but the input effort force is decreased. The same amount of work is done.

Effort force

the force applied to a machine

Resistance force

the force applied by the machine to overcome resistance is called

Input work

work done by you on the machine

Output work

work done by the machine

The Ideal Machine

Input work = Output work (not possible due to friction)

Mechanical advantage

the number of times a machine multiplies the effort force

less than one

When MA is ____ ____ ___, the machine increases the distance moved or the speed

equals one

When the MA is ______ ___, the machine changes the direction of the Fe.

greater than one

When the MA is _______ ____ ___, the machine increases the Fe.

High efficiency machines

produce less heat from friction


W out / W in x 100%

oil grease

You can make machines more efficient with ___ ______.

Simple machine

a machine that does work with only one movement


barsthat are free to pivot or turn about a fixed point called a fulcrum

resistance arm

the distance from the fulcrum to where the resistance force is applied


When you double the distance, you can ____ the force

effort arm

the distance from the fulcrum to where the effort force is applied

first class lever

used to multiply the force and change the direction of the applied force (screwdriver opening a paint can)

second class lever

the resistance froce is located between the effort force and the fulcrum; multiplies force (wheelbarrow)


the length of the arm / length of the resistance arm


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

fixed pulley

a modified first class lever that can multiply force and/or change the direction of the applied force; attatched to something that does not move

moveable pulley

one end of the rope is fixed and the wheel is free to move; it multiplies force by increasing the distance you pull

block and tackle pulley

a system of pulleys made of fixed and moveable pulleys; can have large mechanical advantages

wheel and axle

a machine made up of two wheels of different sizes that rotate together (doorknoibs, pencil sharpener)

larger wheel

the effort force is usually exerted on the

resistance force

the smaller wheel is the


two or more interlocking wheels that may change the direction of the force

inclined planes

sloping surfaces that reduce the amount of force required to do work by increasing the distance over which the force is applied

length of slope / height of slope

For inclined planes, the IMA =

less force

As a ramp/inclined plane is made longer and less steep, ____ _____ is required.

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