Transcript Plants and Photosynthesis

21/07/2015
Pressure and Moments
Newcastle Community High
School
Pressure – some basic ideas
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Describe and draw experiments for each of the following
ideas:
1) Pressure increases with depth
2) Pressure is the same in all directions at a certain depth
Pressure
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Explain how the following work:
1) A sharp knife is easier to use then a blunt knife
2) A drawing pin
3) A woman with stilettos on might damage a floor more
than an elephant would
Pressure
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Pressure depends on two things:
1) How much force is applied, and
2) How big (or small) the area on which this force is
applied is.
Pressure can be calculated using the equation:
F
Pressure (in N/m2) = Force (in N)
Area (in m2)
OR in cm2 and N/cm2
P
A
Some pressure questions
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1) Calculate the pressure exerted by a 1000N elephant
when standing on the floor if his feet have a total area
of 1m2.
2) A brick is rested on a surface. The brick has an area
of 20cm2. Its weight is 10N. Calculate the pressure.
3) 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?
4) (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?
Some examples of pressure
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Gas Pressure
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Hydraulic systems
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Hydraulic systems
Pressure is constant throughout this liquid
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Levers
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Pivot
Effort
Load
3 types of lever
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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)
Moments
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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
Balancing moments
2 metres
200 Newtons
Total ANTI-CLOCKWISE
turning moment = 200x2 =
400Nm
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2 metres
100 Newtons
Total CLOCKWISE turning
moment = 100x2 = 200Nm
The anti-clockwise moment is bigger so the seesaw will
turn anti-clockwise
Balanced or unbalanced?
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Stability
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1. Centre of mass is within
the wheelbase – no problem!
2. Centre of mass is directly above
the edge of the wheelbase –car is on
the point of toppling
3. Car falls over