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# Pressure

## by Daniel McClelland, School Teacher at home on May 18, 2010

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GCSE Physics double award notes

GCSE Physics double award notes

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• Low pressure – air rushes inwards to fill up the less dense volume (rotates anticlockwise in the Northern hemisphere) High pressure – air rushes upwards to escape the denser volume (rotates clockwise in the n.h.)
• Spanish gp winner Mark Webber of Red Bull racing – his car like all racing cars deals with changes in pressure due to the movement of air under and over the structure. 747 aircraft designed to transport heavy loads in total of it’s own mass 81,600 kg a speed of Mach 0.75 500 mph/805 km/h. The basics of flight is due to pressure.
• It doesn’t take any magical or spiritual intervention to lie on a bed of nails – it just takes an understanding of Physics and pressure! Shoe design, not only for comfort but to reduce pressure and
• Why can they not be squished any further? The molecules are too closely packed and have a charge between them that forces them apart.

## PressurePresentation Transcript

• Pressure GCSE Physics
• When else involves changes in pressure?
•
• When is reduced pressure needed?
• Pressure
• Page 57
• Pressure is how an applied force is distributed over an area (force per unit area)
• Pressure = Force / Area
• Newton per metre squared = Newton / metre squared
• N/m 2 = N / m 2
• Another equivalent unit is used for N/m 2 , the Pascal (Pa)
P F A
• Pressure Examples
• Complete the table- (There are 10 000 cm 2 in 1 m 2 )
1. 2. 3. 4.
• Pressure = Force / Area
• P = 10 / 1 = 10 N/m 2
10 N/m 2 0.2 m 2 250 N 12.2 kN/m 2 1 m 2 0.5 m 2 ? 5000 cm 2 10 N 6.1 kN 200 N ? ? ? 1000 Pa 500 N/m 2 Area Force Pressure
• How important are feet?
• 6 800 kg Surface area = 15 cm 2 … And that is why Elephingo or Flamphants don’t exist! Pressure = Force / Area = 68 000 / 0.0015 = 45 333 333 N/m 2 = 0.0015 m 2
• How much pressure are you under?
• What measurements do you need to take?
• My mass =
• My weight = Force =
• Area of my shoe in contact with the ground =
• Total Area =
• My Pressure = Force / Area =
• Extra Questions
• Page 59
• Questions 40, 42, 44, 46
•
• Hydraulics Pg 59
• Some examples of Hydraulic systems-
• Pascal Principle
• Liquids cannot be compressed and the pressure is transmitted equally throughout.
Small Force applied to Master piston BIG resultant force at Slave piston Liquid Volume remains the same, not squishy
• Pressure remains the same… Pressure Area = - Force
• Pascal Principle
• The pressure is transmitted equally in the liquid. This means the force applied at the master piston is MULTIPLIED UP when transferred to the slave piston .
• The slave piston has a greater area than the master piston.
• Therefore the force must be increased at the slave piston to keep the pressure constant.