Pressure in a gasLesson Outcomes:• To know and to be able to explain a demonstration that proves that air exerts a pressure. (C/B)• Describe the simple mercury barometer and its use in measuring atmospheric pressure. (C/B)• Know what a manometer is. (C)

Starter

A rectangular storage tank 4m long by 3m wide is filled with an unknown liquid to a depth of 3m. The unknown liquid has a mass of 4800kg. Calculate:

a) Volume of the unknown liquidb) Density of the unknown liquidc) Weight of the unknown liquidd) The pressure at the bottom of the tank due to the liquid.

Answers

a) 4m x 3m x 3m = 36m3 (3)

b) 4800kg ÷ 36m3 = 133.3 kg/m3 (3)

c) 4800kg x 10N/kg = 48000N (3)

d) 133.4 x 10 x 3 = 4000 Pa

Air pressure demonstration

Air Pressure

• Air pressure is usually 100000 N/m2.• The can contains air particles and is also

surrounded by air particles. They are hitting the sides of the container on the inside and the outside. The vacuum pump removes the air particles from inside the can. The pressure caused by the particles on the outside collapses the can.

Worksheet

• The mercury barometer and manometer pressure gauge.

Recap of the lesson

• To know and to be able to explain a demonstration that proves that air exerts a pressure.

• Describe the simple mercury barometer and its use in measuring atmospheric pressure.

• Know what a manometer is.