Turning Forces

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Turning Forces
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Turning Forces

• You know that forces are a push or pull
• A turning force is another force you come across
  in everyday life
• Opening a Coke can, turning a door handle, or a
  tap, using a tin opener

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The See Saw

• There are two turning forces on a see saw
• The principle of moments states that if a see saw
  is balanced the clockwise moments are equal to
  the anti- clockwise moments

Pivot
Clockwise Moment
Anti-Clockwise Moment
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Turning Forces

• Turning Forces are called Moments
• To work out a moment you use
• Force (N) x Distance from the Pivot (m)
• The units for moments are Newton metres (N m)
• Moments can turn clockwise or anti- clockwise

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The See-Saw

• The see saw is not balanced, because they are
  both the same distance from the pivot
• This means that the heavier kid has the biggest
  turning force

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The See-Saw

• Now it is balanced (in equilibrium) because the
  bigger kid is close to the pivot giving him a
  smaller turning force
• The further away from the pivot the bigger the
  turning force

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Questions on Moments

• If the see saw is balanced, how far from the
  pivot is the 20N?

5 m
2.5m
10 N
20 N

• How much force is needed to balance the
  anti-clockwise side?

10m
10m
5m
10 N
20 N
20 N
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More Questions on Moments

• What are moments measured in?
• Newton metres
• Work out if the following is balanced

20 m
15m
7.5 N
5 N
Anti- clockwise moment Clockwise moment F x D
F x D 5 x 20 7.5 x 15 100 N m 112.5 N m No it
is not balanced it tips clockwise with a moment
of 12.5 N m
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Levers

• If you wanted to open this tin you would use a
  lever

This screwdriver is too small to open the lid
This crowbar is bigger so it can multiply the
force you exert

• It makes work easier

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Labelling Lever Diagrams

• Our body joints have levers
• The pivot can also be called
• the fulcrum

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The Wheelbarrow

• This wheelbarrow can lift more than we can
• The lever from the handles to the fulcrum
  multiplies our effort

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Questions on Levers

• What is the other name for the pivot?
• The fulcrum
• Look at the nutcracker, where is the pivot, load
  and effort

Load
Pivot
Effort
Load
Effort
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Stability

• Stable objects are difficult to knock over

Formula 1 cars have a low centre of gravity so
that they dont topple over
Maradona had a low centre of gravity allowing him
to turn quickly
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Making something stable
Give it a wide base
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How to make things stable
Give it a low centre of gravity
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Unstable objects
The tightrope walker needs the pole to lower his
centre of gravity
Ice Skates have a narrow base
The unicyclist has a high centre of gravity
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Questions on Stability

• Sort these shapes according to their stability
  starting with the most stable

• In each of the following diagrams the arrow is
  the centre of gravity, will these shapes fall
  over?

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Links

• http//www.skoool.ie/skoool/junior.asp?id3403
• http//www.bbc.co.uk/schools/ks3bitesize/science/p
  hysics/forces_motion_9.shtml