1. 26/08/2019
Pressure and Moments
W Richards
Worthing High School

2. Pressure – some basic ideas
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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

3. Pressure Explain how the following work:
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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

4. Pressure F A P Pressure depends on two things:
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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: F A P
Pressure (in N/m2) = Force (in N)
Area (in m2)
OR in cm2 and N/cm2

5. Some pressure questions
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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?

6. Some examples of pressure
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Some examples of pressure

7. Gas Pressure
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8. 26/08/2019
Hydraulic systems

9. Pressure is constant throughout this liquid
Hydraulic systems
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Pressure is constant throughout this liquid

10. Levers
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Pivot
Effort
Load

11. 3 types of lever Load is on other side of pivot (e.g. seesaw)
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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)

12. Moment (in Nm) = force (in N) x distance from pivot (in m)
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

13. Balancing moments 2 metres 2 metres
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2 metres
2 metres
Total ANTI-CLOCKWISE turning moment = 200x2 = 400Nm
Total CLOCKWISE turning moment = 100x2 = 200Nm
200 Newtons
100 Newtons
The anti-clockwise moment is bigger so the seesaw will turn anti-clockwise

14. Balanced or unbalanced?
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15. Stability 1. Centre of mass is within the wheelbase – no problem!
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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