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Table Of Content
Definition
Centrifugal Force is the force that comes into play when a body is moving in a circular path, and keeps the tendency to regain its natural straight line path.
Introduction
It is the natural tendency of a body that it moves uniformly along a straight line.If centripetal force is applied on the body,it is forced to move along a circle,but is has constant tendency to regain its natural straight line path.This tendency gives rise to a force called ‘Centrifugal Force’. Centrifugal force can be regarded as the reaction of centripetal force. As forces of action and reaction are always equal and opposite,therefore,magnitude of centrifugal force is same as that of centripetal force but the direction is opposite to the direction of centripetal force.Centripetal force acts along the radius in inward direction whereas centrifugal force acts along the radius and away from the centre of the circle. For example,when a stone tied to one end of a string is rotated in a circle,centripetal force F1 is applied on the stone by the hand in inward direction.In turn, the hand is pulled outwards by centrifugal force F2,acting on it,due to tendency of the stone to regain its natural straight line path. It is shown in fig (1)
Fig (1)
A Stone rotated in horizontal Circle
Centrifugal Force (A pseudo Force)
There are certain situations in which we feel that the body is acted upon by a force,but actually there is no force on the body.Such an apparent force is called a Pseudo force(or Centrifugal force).Suppose a body of mass ‘m’ is placed on a circular table,which is rotating with a uniform angular velocity around a nail passing through the centre of the table.Suppose the linear velocity of table is ‘V’ and body is at a distance ‘r’ from the nail. When table rotates, body also rotates. To keep the body at rest on the table it must be tied to the nail by a string.
Fig (2)
Demonstration of Centripetal and Centrifugal Force
A man standing on earth and looking at the rotating table will observe that the body is revolving around the nail and has centripetal force equal to “mv2/r”.This is a real force and provided by tension in the string.To another man who is standing on the table (Fig 2(b)),the body appears at rest because its position is not changing with respect to the man and he observes no force,acting on the body.It happens because body is actually acted upon by an inward force mv2/r,so the man feels that a force of magnitude mv2/r is also acting in outward direction,hence net force becomes zero.This apparent force is called Centrifugal Force.If the string is cut then the person on table will see the body is moving radially outwards from the table whereas the man standing an earth will observe the motion of body tangentially outwards.
Some illustrations of Centrifugal Force
Centrifuge
It is a device used to separate lighter particles in suspension from the more dense liquid in which they are contained.Such a mixture is poured into the container of the centrifuge, which inturn,is whirled at high speed in a horizontal circle.The lighter particles move towards the axis of rotation as explained below.
A mass ‘m’ of dense liquid revolving at a distance ‘r’ from the axis of rotation of the centrifuge requires a centripetal force “mrw2”, where ‘w’ is the angular velocity of centrifuge.The required centripetal force is provided to this mass of liquid by the pressure gradient existing in the liquid. If in place of this mass of liquid, lighter particles of mass m1 (m1<m) are present, then centripetal force (mrw2) on the dense liquid will be greater than the centripetal force (m1rw2) in the lighter particles.As a result,the lighter particles move towards the axis of rotation under the effect of the net force (m–m1).r.w2.When the centrifuge is stopped,the suspension in the container is found at the top and the clean liquid at the bottom.
It follows that the heavy particles in a suspension will collect at the bottom of the container of the centrifuge, leaving clear liquid at the top.On the basis of this principle,
- Cream is separated from the milk in cream separator
- The wet clothes are dried by dry cleaners in the drying machines
- Centrifuges are used to separate honey from the wax
Centrifugal Pump
By using this,it is possible to transfer large quantities of liquid against low back pressure. These pumps are also used as Exhaust fans and blowers.The function of this pump is based on Centrifugal Force.
Centrifugal Governors
By the use of Centrifugal force, the speed of an engine can be automatically controlled.
References
- Pradeep’s Fundamental Physics (XI)
- Modern’s abc of Physics (vol.I)
- Mootan physics by Kumar Mitlal (XI)