# Work and Machines- Chapter 5

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### Work

the transfer of energy that occurs when a force (push or pull) moves on an object

### Energy

the ability to cause change or do work

### Energy

is transferred from the object that is doing the work to the object on which the work is done (i.e. carrying a box upstairs)

### Work

force x distance (fd)

### Newtons

force is measured in

### Meters

distance is measured in

### Joules

work is measured in

### Joules

also known as Newton meters

### Power

the amount of work done in a certain amount of time; the rate at which work is done

work / time

### Watts

power is measured in

energy / time

### Machine

a device that makes work easier

### Machines

increase the force applied to the object

### Machines

can be powered by a force applied by a person

### Machines

they can be simple or complex

### Machines

make work easier by changing the direction of an applied force (i. e. pulling down on blind sring as blinds fold up)

### Machines

can increase the force by applying a smaller force over a a large distance versus a larger force over a shorter distance

### 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

De

Dr

### mechanical advantage

Fr / Fe or De / Dr =

### 2.5 N

If Fe = 100 N and Fr = 250 N, what is the MA?

### 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.

### efficiency

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

### High efficiency machines

produce less heat from friction

### Efficiency

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

### Levers

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

### half

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)

### IMA

the length of the arm / length of the resistance arm

Le / Lr

### pulley

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

### gears

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.

### screws

inclined planes wrapped in a spiral around a cylindrical post (twisted inclined planes

### Wedge

inclined plane with one or two sloping sides that change the direction of the effort force (knife, axe, edge of scissors

### compound machine

two or more simple machines used together

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