Thursday, May 17, 2007

X-revision Pressure in Fluids; Atmospheric Pressure

What is a fluid?
A substance which can flow is called a fluid. All liquids and gases are thus fluids.

What is thrust?
The force acting normally on a surface is called the thrust.

What is pressure?
The thrust on unit area of the surface is called the pressure.

One pascal is defined as the pressure exerted on a surface of area of 1 m2 by a force of 1 N acting normally on it.

A fluid contained in vessel exerts pressure at all points and in all directions.

Total pressure in a liquid at a depth h = Atmospheric pressure + pressure due to liquid column.

What is Pascal’s law?
Pascal’s law states that the pressure exerted anywhere in a confined liquid is transmitted equally and undiminished in all directions throughout the liquid.

What is a barometer?
An instrument used to measure the atmospheric pressure is called a barometer.

Decrease in atmospheric pressure with altitude is due to the following two factors;

(i) decrease in height of air column which produces a linear decrease in the atmospheric pressure.
(ii) decrease in density of air which makes the decrease in atmospheric pressure less rapid.

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