Daniel Bernoulli gave a basic principle of fluid dynamics, understanding of this principle helps us to understand how an aeroplane flies, how a spinning ball curves, how a chimney functions, why a fast moving train pulls the things closer to it etc. It’s an important principle of physics which makes us to understand the phenomenons occurring in our daily life.
In very crude form Bernoulli’s Principle states that where the velocity of flow increases pressure decreases and vice-a-versa.
1. How Aeroplane gets lift
When aeroplane moves on runway the shape of the wings of aeroplane are designed in such a way that air flowing on upper side of wing has to cover more distance in same time than the air flowing underneath. Hence on upper side of the wing air velocity is higher than the lower side, so the pressure is lower on upper side of wing and wing of aircraft gets lift when air tries to move from higher pressure to lower pressure.
2. Why a fast moving train pulls nearby objects
Air close to fast moving train also moves in the direction of train due to higher velocity of airflow close to train pressures becomes lesser and surrounding air rushes from high pressure to low pressure area and hence things are pushed towards the train. People standing on platforms are advised to move away and keep their belongings away from fast moving train to avoid accidents.
3. Why a spinning ball curves
When ball is thrown with a spin, ball as a whole moves against the surrounding air but there is portion of ball spinning in the direction of air and opposite part against the air. Relative velocity of air spinning in the direction of air becomes more but in opposite direction spin of ball opposes airflow and velocity of air is relatively lesser. As per Bernoulli’s Principle more air velocity leads to lesser pressure and air moves from high pressure to lower pressure and pushes the ball which leads to curved path.
In heavy winds, velocity of air is stopped by walls of house bur velocity is very high on roof top which creates lower pressure on roof top, but inside the house air velocity is very less and hence pressure is very high as compared to rooftop. High pressure air inside the room tries to move towards low pressure area and hence roof is lifted and blown away sometimes.
5. How atomizer works
If we see the diagram of atomizer carefully, pressure at point “A” and point “B” is same under normal condition. When rubber bladder “R” is squeezed air rushes from nozzle at point “B” and due to high air velocity pressure drops down and fluid at point “A” rushes from high pressure to low pressure and gets sprayed by high velocity air at point “B”. Carburetor also works similarly.
6. How chimney works
Wind velocity outside the house is normally higher than inside, due to higher velocity above the nozzle of the chimney pressure is lower and air rushes from high pressure to low pressure i.e smoke is blown away by chimney. Thus we can easily understand why chimneys work better when there is good wind flow.