**Mechanical Properties of Fluids – Notes**

**Physical quantities –fluids**

A fluid is any matter that has tendency to flow. All liquids and gases are together referred to as fluids.

External force acting per unit area on a solid is called stress.

Pressure is defined as force exerted per unit area.

Density of a fluid is the ration of its mass to its volume.

**Variation in pressure atmospheric pressure; gauge pressure**

The pressure on an object submerged in a liquid is independent of the area of cross section.

Atmospheric pressure at any point is equal to the weight of a vertical column of air of unit cross sectional area extending from that point to the top of the earth’s atmosphere.

Gauge pressure is the difference between absolute pressure and atmospheric pressure at any given point.

Gauge pressure is the same at all points at the same horizontal level or depth.

Atmospheric pressure can be measured using a barometer or an open tube manometer.

**Archimedes’ Principle**: when a body is partially or completely immersed in a fluid at rest, the fluid exerts an upward force of buoyancy, which is equal to the weight of the displaced fluid.