Pressure and Moments

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Pressure and Moments
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Pressure some basic ideas

• Describe and draw experiments for each of the
  following ideas
• Pressure increases with depth
• Pressure is the same in all directions at a
  certain depth

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Pressure

• Explain how the following work
• A sharp knife is easier to use then a blunt knife
• A drawing pin
• A woman with stilettos on might damage a floor
  more than an elephant would

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Pressure

• Pressure depends on two things
• How much force is applied, and
• How big (or small) the area on which this force
  is applied is.
• Pressure can be calculated using the equation

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Some pressure questions

• Calculate the pressure exerted by a 1000N
  elephant when standing on the floor if his feet
  have a total area of 1m2.
• A brick is rested on a surface. The brick has an
  area of 20cm2. Its weight is 10N. Calculate the
  pressure.
• A woman exerts a pressure of 100N/cm2 when
  standing on the floor. If her weight is 500N
  what is the area of the floor she is standing on?
• (Hard!) The pressure due to the atmosphere is
  100,000N/m2. If 10 Newtons are equivalent to 1kg
  how much mass is pressing down on every square
  centimetre of our body?

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Some examples of pressure
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Gas Pressure
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Hydraulic systems
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Hydraulic systems
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Levers
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3 types of lever
Load is on other side of pivot (e.g. seesaw)
Load is outside the effort, (e.g. biceps)
Load is inside the effort (e.g. wheelbarrow)
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Moments
A moment is a turning force, e.g. trying to
open or close a door or using a spanner. The
size of the moment is given by
Moment (in Nm) force (in N) x distance from
pivot (in m)
Calculate the following turning moments
5 metres
100 Newtons
2 metres
200 Newtons
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Balancing moments
The anti-clockwise moment is bigger so the seesaw
will turn anti-clockwise
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Balanced or unbalanced?
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Stability