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FORCES, SIMPLE AND COMPLEX
MACHINES
What do these pictures tell
you?
What do they have in
common?
ACTIVITY
Underline or find the following
words in the following texts.
- Force
- Kick
- Exert
- Push
- Move
CONTACT FORCE
Everyone has a basic understanding of the concept
of force from everyday experience.
When you push your empty dinner plate away, you
exert a force on it. Similarly, you exert a force on a
ball when you throw or kick it. In these examples,
the word force is associated with muscular activity
and some change in the velocity of an object.
Forces do not always cause motion, however. For
example, as you sit reading this book, a
gravitational force acts on your body and you still
remain stationary. As a second example, you can
push (in other words, exert a force) on a large
boulder and not be able to move it.
SIMPLE MACHINES
Once upon a time a person needed to move
something heavy. He or she picked up a
long stick and stuck it under the edge of
the heavy object and then pushed down
on the other end of the stick. And the first
simple machine was invented. Simple
machines are just that. The simplest form
of using one thing to accomplish
something faster or better. A tool. They
were the first ones created and we still use
them today.
• A pulley is a simple machine that
uses grooved wheels and a rope
to raise, lower or move a load.
• Pulley are wheels and axles with a
groove around the outside
• A pulley needs a rope, chain or belt
around the groove to make it do
work
LEVER
A lever is a stiff bar that rests on a
support called a fulcrum which
lifts or moves loads.
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
WEDGE
• A wedge: Two inclined planes
joined back to back.
WEDGE
Wedges are used to split
things.
WHEEL AND AXLE
• The wheel and axle is 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
Wheel and Axle
In this machine a wheel or spoke is
locked to a central axle so that
when one is turned the other must
turn.
In reverse, a short powerful force at
the axle will move the wheel's
edge a greater distance.
INCLINED PLANE
An inclined plane is a slanting surface
connecting a lower level to a higher
level.
INCLINED PLANE
• An inclined
plane is a flat
surface that is
higher on one
end
• Inclined planes
make the work
of moving
things easier
SCREWS
• A screw is an inclined plane
wrapped around a shaft or
cylinder.
• The inclined plane allows the
screw to move itself when
rotated.
SCREWS
• A screw is an inclined plane
wrapped around a pole which
holds things together or lifts
materials.
• Two or more simple machines
working together to make work
easier.
Examples: Wheelbarrow, Can
Opener, Bicycle
VIDEO
• https://www.youtube.com/wat
ch?v=4JWi2tkplYs
Web sites
• http://legacy.mos.org/sln/Leonard
o/InventorsToolbox.html
• http://www.engquest.org.au/stud
ents-smup.cfm#Screws?CFID=1231605&CF
TOKEN=49727120
• http://www.mikids.com/Smachine
s.htm