What is a Fluid?
Matters like liquids and gases that do not have any definite shape or size and have a tendency to flow are known as Fluids. e.g. water, air, etc.
Fact Check:
Which of the following is not fluid?
Cold Drink
Engine Oil
Helium
Glass
None of the above
Which weighs more, a ton of feathers or a ton of bricks? This old riddle plays with the distinction between mass and density. A ton is a ton, of course; but bricks have much greater density than feathers, so we are tempted to think of them as heavier.
Density, as you will see, is an important characteristic of substances. It is crucial, for example, in determining whether an object sinks or floats in a fluid. Density is the mass per unit volume of a substance or object.
In equation form, density is defined as
ρ=mV
Example:
A reservoir has a surface area of 50km2 and an average depth of 40m. What mass of water is held behind the dam?
Solution:
Solving equation ρ=mV
for m gives m=ρV
The volume V of the reservoir is its surface area A times its average depth h:
V
=Ah=50km240m
=2×109m3
The density of water ρ is 1×103kgm−3.
Substituting V and ρ into the expression for mass gives
m
=1×103kgm−32×109m3
=2×1012kg
Try it Out:
A solid ball has a mass of 180g and a radius of 8cm. What is the density? (in gcm−3)