C2 Pressure
Cards (15)
- Pressure (Pa) is force per unit area.
- Pressure in liquid:
- increases with depth
- increases with density
- does not depend on shape of container
- Atmospheric pressure is the pressure exerted by the weight of one column of air in the atmosphere per unit area.
- P(atm) = h x p x g
- Instruments made to measure atmospheric pressure:
- barometer - simple mercury barometer, fortin barometer, aneroid barometer
- Instruments used to measure gas pressure:
- manometer
- bourdon pressure gauge
- Advantages of mercury over water manometer:
- higher density
- lower freezing point
- more visible (silvery liquid)
- higher boiling point
- Pascal's principle : pressure exerted on a fluid in an enclosed system is uniform in all directions.F1/A1 = F2/A2
- Multiplication factor= output force / input force= area of large piston / area of small piston
- Archimedes' principle: The buoyant force of a fluid is equal to the weight of the fluid displaced.
- Buoyant force (upthrust force) is the force acting upwards on an object when fully of partially immersed in fluid due to difference in pressure between upper and lower surface.
- Application of Archimedes' principle:
- hydrometer - measure density of a liquid
- submarine - use of ballast tank
- plimsoll line - indicates maximum depth
- hot-air balloon - cold air will sink, hot air will float
- Bernoulli's principle : as velocity of fluid increases, pressure decreases.
- Venturi Effect : fluid pressure decreases when flowing through narrow part of Venturi tube.Narrower tube = higher velocity of fluid = lower pressure in fluid
- Examples of Bernoulli's and Venturi :
- Lift force - difference in pressure
- bunsen burner - gas at high velocity, low pressure suck in surrounding air with lower velocity, high pressure
- safety lines at railways - high velocity, low pressure produced by trains suck in surrounding air
- aero-foil shape :
- - low velocity produce high pressure upwards
- - high velocity produce low pressure downward