# Gravation Thrust

Topics: Density, Buoyancy, Fundamental physics concepts Pages: 4 (861 words) Published: January 7, 2013
THRUST

• The force acting on a body perpendicular to its surface is called thrust. • Thrust is the total force acting on the surface of the body. • Thrust per unit area is pressure

Pressure = Thrust
Area

S.I unit of pressure is N/m2 or Pascal

EVERYDAY OBSERVATIONS RELATED TO PRESSURE:

• School bags have wide straps so that the weight of the bag falls over a large area of the shoulder producing less pressure on the shoulder. Due to this less pressure, it is comfortable to carry the heavy schoolbag.

• A sharp knife cuts well than a blunt knife because the edge being very thin, the force of our hand falls over a very small area of the object, producing a large pressure. And this large pressure cuts the object easily. On the other hand the blunt knife has a thicker edge due to which the force of our hands falls over a large area producing lesser pressure.

• The tip of a thumb pin is sharp so that due to its sharp tip, the pin may put the force on a very small area of the wooden board producing a large pressure sufficient to pierce the board.

BUOYANCY

While bathing we notice that the mug of water suddenly appears heavier as soon as it comes above the water surface.
Similarly, when a fish is pulled out of water, it appears to be heavier in air than inside the water. All objects whether completely immersed inside a liquid (or fluid) or partially inside, appear to be lighter than in air.

Objects appear to be less heavy in a fluid or in any liquid because the liquid or water exerts an upthrust on the objects immersed in it.
The upward force exerted by a fluid on an object when it is partly or wholly immersed in it is called buoyant force. The Buoyant force is also known as the upthrust.

(a) A stone is weighed in air
(b) The stone weighs less when immersed in a liquid because of the buoyant force exerted by the liquid on it in the upward direction....