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

Power

work / time

Watts

power is measured in

Power

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

effort distance

De

resistance distance

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

IMA

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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