aim: what are simple machines

AIM: What are Simple Machines

Vocabulary

Definition of a Simple Machine

Makes work easier by changing either

• The amount of the force needed

•Or the direction of the force

Inclined PlanesAn inclined plane

is a flat surface that is higher on one end

Inclined planes make the work of moving things easier

MECHANICAL ADVANTAGE

Is a measure of the “goodness” of a machine

The higher the MA the better?What force acts/work against MA?EFFICIENCY:

less friction = greater Efficiency

Inclined Plane Sloped surface used

to make lifting easier

MA =

height

length

l

h

length of ramp

height of ramp

Screws A screw is an

inclined plane wrapped around a shaft or cylinder.

The inclined plane allows the screw to move itself when rotated.

The Screw

A screw is an inclined plane wrapped around a rod

Use to hold objects together

MA =2 rr

lg

gap

twice the radius of rod

length of gap

radius of rod

Note: 2 r = d

Don’t measure the top!

Wedges Two inclined

planes joined back to back.

Wedges are used to split things.

Wedge A wedge is an

inclined plane with two sloping surfaces

Used to cut

MA =

height

width

h

w

height of wedge

width of wedge

Wheels and Axles The wheel and axle

are a simple machine

The axle is a rod that goes through the wheel which allows the wheel to turn

Gears are a form of wheels and axles

Pulleys

Pulley are wheels with a groove around the outside

A pulley needs a rope, chain or belt around the groove to make it do work

Three Types of Levers

All levers have a fulcrum

Levers-First Class In a first class lever

the fulcrum is in the middle and the load and effort is on either side

Think of a see-saw

Levers-Second Class In a second class

lever the fulcrum is at the end, with the load in the middle

Think of a wheelbarrow

Levers-Third Class In a third class lever

the fulcrum is again at the end, but the effort is in the middle

Think of a pair of tweezers

Levers A lever is a bar that

is free to move about a pivot point

A lever has three parts effort arm fulcrum resistance arm

fulcrum

resistance arm

effort arm

Types of Levers

Levers are grouped into three classes

Third Class

Second Class

First Class

First Class Lever Fulcrum in the

middle of the bar

Examples Balance Paint can Teeter-totter

effort force

resistance force

Second Class Lever Resistance force

(load) is in the middle

Examples wheel barrow door nut cracker

resistance force

effort force

Third Class Lever Effort force is in the

middle

Examples baseball bat fishing pole canoe paddle broom

resistance force

effort force

Mechanical Advantage of Levers

MA =

effort armresistance arm

le

lr

length of effort arm

length of resistance arm

Wheel and Axle Two wheels of different

sizes

Connected and move together

Examples door knob pencil sharpener screw driver

smaller

wheel

larger wheel

Wheel and Axle

A wheel and axle act like a circular lever.

small force in

Large force out

• By turning the large blue wheel,

• The smaller yellow axle also turns.

Wheel and Axle

• Or, the two can be used in reverse.

Small distance

in

Large distance

out• By turning the small

yellow axle

• The larger blue wheel also moves.

MA of Wheel and Axle

• MA = rw

ra

radius of wheel

radius of axle

wheel

axle

Pulleys

A pulley is a surface with a chain or rope going around

Used to lift heavy objects

Two types Fixed movable

Types of Pulleys

Fixed Pulley Pulley is fastened

into position

Changes the direction of force

Does not magnify the force

fixed pulley

Types of Pulleys

movable pulley

• Movable Pulley– Pulley is fastened to

the load

– Load is shared between both ends of the line

– Only half the force is needed to lift the load

MA of a Pulley MA = number of

lines supporting the load

Don’t count the line that is being pulled.

MA = 1

One line is supporting the load.

MA = 2

Two lines are supporting the load.

Efficiency

• Efficiency is the ability to convert input work into actual work output.

no machine is perfect

loss caused by friction

Calculating Efficiency

WO

WI

• Efficiency = 100

Input Work

Output Work

Ideal machines have 100% efficiency.

Compound Machines

A compound machine is a combination of simple machines that work together.

Simple Machines Simple Machines

can be put together in different ways to make complex machines

A complex machine is one or more simple machines