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pulling of bullock cart, etc. Different example, iron nails are attracted by a
types of contact force include the magnet.
following. (ii) Electrostatic forces : Forces between
(ii) Frictional Force : Force that can cause a charged particles are called
change in state of motion is called as electrostatic forces. Like charges repel
frictional force. Frictional force is the each other and unlike charges attract
force that acts in a direction opposite to each other.
that of motion. Examples of frictional (iii) Gravitational force : The force that is
force include : responsible for pulling an object
On a carrom board, striker comes to towards the earth is called as
rest by itself. gravitational force. For example, we do
Bus stops by itself when brakes are not fly but stand on the earth due to
applied. the gravitational force.
Ball stops itself on the ground after
traveling a little distance.
Frictional force always acts between two
surfaces, surface of the object in motion
and the surface on which it moves.
PRESSURE
Definition : Force per unit area exerted
vertically on the surface of an object is called
pressure. Pressure is denoted by P.
Carrom board Bus Force F
Pressure = or P =
Area A
Pressure is directly proportional to force and
inversely proportional to the area. This means,
more the area, less will be the pressure and
Ball at rest more the force higher will be the pressure.
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(b) Non-contact forces : These forces come S.I. unit for measurement of pressure is N/m
into play even when the objects are not in or 1 Pascal in honour of Blaise Pascal.
contact. Numericals :
Different types of non-contact force 1. Calculate the pressure produced by a force
include the following:- of 800 N on an area of 2m 2
(i) Magnetic force : Forces exterted by a Solution : Pressure = Force
magnet is called magnetic force. For Area
The largest desert in the world, the Sahara is spread over 3,500,000 sq. miles.
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