Atmospheric pressure is defined as the pressure exerted on an object by the weight of the air above it.
Why do we not feel atmospheric pressure?
This is because the pressure of the blood in our blood vessels and that of the other fluids present in the body balances out the atmospheric pressure. Atmospheric pressure is measured using an instrument called a barometer.
VARIATION OF ATMOSPHERIC PRESSURE WITH ALTITUDE
The altitude of a place is its height above sea level. The atmospheric pressure at a place depends on its altitude and decreases as we go up.
We know that atmospheric pressure at a place is the force exerted by the weight of the air column above us decreases. This means its weight decreases, and, therefore the atmospheric pressure is lower at higher places.
MEASURING PRESSURE
The instrument used to measure pressure is a pressure gauge. The simplest type of pressure gauge is an open-tube manometer, which measures pressure difference. A manometer consists of a U-shaped tube containing a liquid (sometimes water).
VARIATION OF LIQUID PRESSURE WITH DEPTH
As we go deeper beneath the surface of a liquid, pressure increases with depth. Deep under the sea, the pressure exerted by water is much greater than at the sea level. Deep-sea divers use special suits called diving suits and buoyancy compensators to combat the weight of their diving equipment and the water pressure at great depths. Dams are made stronger and thicker at the bottom than at the top to withstand the high pressures at greater depths.