Physical and Non-physical quantities | Definition , differences and examples

Physical quantities can be measured in a proper unit and it has a numerical value . Physical quantities are verified scientifically and help us to define laws of physics . 
eg. mass, amount of substance, length, time, temperature, electric current, light intensity, force, velocity, density, momentum , energy .

And Non- Physical quantities are those quantities that can not be measured by any device ,  does not have unit or  magnitude themselves .  Sometimes these quantities can be compared to each other .
eg. Rudeness, Love , Happiness,  Sadness , Proudness, Respect, Pride, Hate, Angry, Loyalty and Stupidity .

Barometer and Manometer | Working principle , Applications and Differences

Barometer is a device used to measure atmospheric pressure . In principle ,  any liquid can be used to fill the Barometer,  but mercury is the substance of choice because its high density makes possible an instrument of reasonable size . It uses liquid mercury to predict the weather by tracking atmospheric pressure changes resulting from the movement of warm and cold weather systems .

Variation of pressure with Depth in a fluid

We know that in an statics fluid pressure in horizontal direction will be constant because  of equi-pressure surface but in case of vertical Variation it’s Vary .If the weight of the fluid can be neglected, the pressure in a fluid is the same throughout its volume. But often the fluid’s weight is not negligible and under such condition pressure increases with increasing depth below the surface .
dp/dy = ρg . ( This is the general expression  of variation of pressure with depth  ) .