- The efficiency of an energy source is hence also measured by:
$
\text { Efficiency }=\frac{\text { Power output }}{\text { power input }}
$
- In Physics, density refers to the degree of compactness of a substance. Pure water has a density of 1.00. Dersity is given by:
$p=\frac{m}{v}$
p=density
m=mass
v=volume
- To find the relative density of a fluid (relative density is how many more times dense a Hid is compared to water), the following two formulae ale us
relative density $=\frac{\text { density of substance }}{\text { density of water }}$
relative density $=\frac{\text { mass of substance }}{\text { mass of same volume of water}}$
- Unlike density, Pressure refers to the constant physical force exerted on an object by somet hing in contact with it.
- Measured in Pascals $(\mathrm{Pa}) \cdot 1 \mathrm{Nm}^{-1}$ = $1 \mathrm{~Pa}$.
Pressure is defined by:
$p=\frac{f}{A}$
f= force
A=Area