The force acting perpendicularly on a
surface is called thrust.
The thrust/force acting on unit area of
the surface is called pressure.
unit of thrust is Newton.(N)
SI unit of pressure is Pascal.(Pa)
Let’s know more about thrust and
If we push hard on a piece of wood with our thumb, the
thumb doesn’t go into the wood But if we push a
drawing pin into the wood with the same force of our
thumb, the drawing pin goes into the wood.
Our thumb doesn’t go into the wood because the force of
thumb is falling on a large area of the wood due to which
the ‘force/area’(pressure)on the wood is small .Whereas
in the case of drawing pin the area of pin falling on
wood is small therefore the pressure is more and pin
goes into the wood.
Pressure is the force acting on a unit area of the
We have just defined pressure in terms
of force. Pressure can also be defined in
terms of another term called ‘thrust’.
The force acting on a body
perpendicularly to its surface is
Actually, thrust is the total force acting
on the surface of a body.
When an obj. is placed in a liquid, the
liq. exerts an ‘upward force’ on it .
Ex. when a piece of cork is held below
the surface of water by applying the force
of our thumb and then released, the cork
immediately rises to the surface. It
appears as if some upward force is
exerted by water on the cork which pushes
it to the surface.
an object is immersed in a
liquid, it experiences an upward force.
This upward force is called buoyant
force. Thus the upward force acting
on an object immersed in a liquid is
called buoyant force(upthrust)
When a solid object is immersed in a
liquid, an upward force (upthrust) is
experienced which is equal to the weight
of liquid displaced by the object.
In other words:
acting on an obj.
= liquid displaced
by that obj.
Some substances appear to be heavy
whereas others are light. For ex., iron is
heavier than aluminium and water is
heavier than alcohol. In physics we
describe the lightness or heavyness of
different substances by using the word
density. The density of substance is
defined as mass of the substance per unit
Density =mass of the substance
volume of the substance
I got a wonderful knowledge by making
this power point presentation as I get to
know more about
thrust, pressure, density, archimede’s
I am very thankful to my IT sir and