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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 Planes. An inclined plane is a flat surface that is higher on one end - PowerPoint PPT Presentation
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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