Page 167 - Physics

Pressure
Outlet valve Intake valve

(a)
Leather washer Metal rod

(b)

(c)
Figure 7.38: Operation of a bicycle pump

Task 7.8

Visit a nearby bicycle repair shop and observe a bicycle pump. Discuss its mode of
operation. Draw a well-labelled diagram of the bicycle pump. What is the signifi cance
of the intake and outlet valves?

ICT corner

Visit https://phet.colorado.edu and select the simulation titled "Gas
properties" as the illustration of the marble pile model to demonstrate
and visualise the existence of atmospheric pressure

Chapter summary
1. Pressure is defi ned as the force acting normally per unit surface area.
Force
Pressure = ⋅
Area
2. The SI unit of pressure is N/m . Other units of pressure are Pascal (Pa),
2
atmosphere (atm), torr and mmHg.
3. Fluids (liquid or gas) exert pressure on an immersed object and the walls of their
container. The pressure in the fl uid at a depth h is given by P = ρgh. Pressure
in a liquid depends on the density of the liquid and the depth.
4. Pascal’s principle states that, any pressure applied on the surface of an enclosed
fl uid will be transmitted equally to all points in the fl uid. This principle is the basis
for the hydraulic lift, hydraulic press and hydraulic brakes. Pressure in liquids
and gases can be measured with a manometre that works on Pascal’s principle.
5. Air pressure is measured using either a Fortin barometre or an aneroid barometer.
6. Standard atmospheric pressure at sea level is 101.3 kPa.
7. Siphons, syringes, lift and force pumps are used to transfer liquids and gases.

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