Kepler’s laws of planetary motion | Definition , Diagrams , Equations ,Facts and Solved Examples .

Johannes Kepler used empirical observations, and sophisticated calculations to arrive at the famous Kepler’s laws of planetary motion, published in 1609 and 1619. What is particularly significant about Kepler’s laws is that they challenged the prevailing world’s view, with the Earth in the center of the universe (a geocentric theory) and the Sun and all the planets and stars orbiting around it, just as the Moon does .

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  ) .