Force, What is force?, Formula for Force, how many types of force, non-contact force, contact force

What is force?

Force can be defined as the physical cause that tends to change the resting position or uniform motion or to change the shape and size of the body.

Formula for Force



M = mass

A = acceleration

how many types of force

Forces are classified as contact and non – contact forces.
Forces can be applied on a body by making physical contact or otherwise.

What is contact force?

Forces which act on a body through physical contact are contact forces.

Example of contact force

  • Mechanical force
  • Muscular Force
  • Frictional force

Mechanical force

To hit a nail into a wall, we use a hammer.  The force exerted by the hammer on the nail rives into the wall.  Thus, in this case, the force makes a physical contact and displaces the mail Such a force is called contact force or in this case, it can also be called mechanical force.

Frictional force

Frictional force is defined as the force which opposes any tendency for relative motion.

What is non-contact force?

Forces which act on a body without making any physical contact with the body are known as non – contact forces.

Example of non- contact force

  1. Gravitational force
  2. Electrostatic Force
  3. Magnetic Force

Magnetic Force

Place a small iron piece near a magnet.  The iron piece moves wards the magnet.  This force applied by the magnet is called magnetic force.
Magnetic force is a non – contact force, since the iron piece experiences a force though there is no physical contact.

Gravitational Force

A ball thrown vertically upwards returns to the ground after some time . This is on account of the attractive force the Earth exerts on the ball . Similarly , the Earth also exerts an attractive force on celestial bodies such as the moon , the sun , the planets , etc. This force of attraction between any two masses is known as gravitational force.

Units of Force

Absolute unit of force:
If m = 1 unit, a = 1 unit, then the value of F = 1 unit
C.G.S.  unit of force is ‘dyne‘ and S.I.  unit of force is ‘newton‘ (N).
Dyne: It is the force which when acting on a body of mass one gram produces in it an acceleration of 1 cm s-2 in its direction.
Newton: It is the force which when acting on a body of mass 1 kg produces in it an acceleration of 1 m s-2 in its direction.
 1 newton (N) = 1 kg × 1 m s-2

Force example

What is the force exerted by a bullock in pulling a cart of mass 100 kg and accelerating at a rate of 1.5 ms-2?
m = 100 kg
a = 1.5 m s-2
From Newton’s second law,
F= ma
F= 100 kg × 1.5 m s-2 = 150 N
An object of mass 10 kg is moving with an initial velocity of 10 ms -1. A constant force acts for 4s on the object giving it a speed of 2 m s-1 in the opposite direction. Find the acceleration and force.
m=10 kg
u= 10 m s-1
Let the final velocity in the opposite direction be v.
t= 4s
v= -2 m s-1
A=v-u/t(From the equations of motion,v=u+at)
a= -2-10/4 = -12/4 = -3 s-2
The negative sign shows that it is retardation.
From Newton’s second law,
F= ma = 10×-3 = -30 N
Retarding force = 30 N.

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