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Nature of equilibrium is decided by the behavior of the body, when it is disturbed from its equilibrium position.

We encounter different kinds of equilibrium. Take the case of a tennis ball and a paper weight, which are placed on a table. A slight force on tennis ball makes it to roll and finally drop off the table, whereas paper weight hardly moves from its position on the application of same force. Two bodies, therefore, are equilibrium of different nature. In this module, we shall not go for details of every aspects of equilibrium; but will limit ourselves to broader classification, which is based on energy concept.

We shall further limit the analysis of equilibrium to the context of equilibrium in conservative force field like gravity. A body in conservative force field possesses mechanical energy in the form of kinetic and potential energy. Potential energy, as we know, is exclusively defined for conservative force field and is a function of position. In this module, we shall attempt to correlate potential energy with the nature of equilibrium in following categories :

  • Stable
  • Unstable
  • Neutral

Disturbance and equilibrium

In order to appreciate the role of potential energy about equilibrium, we first need to visualize equilibrium in the light of external disturbance. We should keep this in mind that disturbance that we talk about is a relatively small force.

A typical set of example to illustrate the nature of equilibrium consist of three settings of a small ball (i) inside a spherical shell (ii) over the top of a sphere/ spherical shell and (iii) over a horizontal surface. These three settings are shown in the figure.

Nature of equilibrium

The equilibrium of a small spherical ball in three different positions.

What do we expect when the ball inside the shell is slightly disturbed to its left. A component of gravity acts to decelerate the motion; brings the ball to a stop; and then accelerates the ball back to its original position and beyond. Restoration by gravity continues till the ball is static at the original position, depending upon the friction. The equilibrium of the ball inside the shell is “stable” equilibrium as it is unable to move out of its setting. The identifying nature of this equilibrium is that a restoring force comes into picture to restore the position of the object.

A ball inside a spherical shell

Force on the small spherical ball.

Let us now consider the second case in which the ball is placed over the shell. We can easily visualize that it is difficult to achieve this equilibrium in the first place. Secondly, when the ball is disturbed with a smallest touch, it starts falling down. The gravity here plays a different role altogether. It aids in destabilizing the equilibrium by pulling the ball down. The equilibrium of the ball over the top of the sphere is called “unstable” equilibrium. The identifying nature of this equilibrium is that once equilibrium ends, there is no returning back to original position as there is no restoring mechanism available.

Questions & Answers

if three forces F1.f2 .f3 act at a point on a Cartesian plane in the daigram .....so if the question says write down the x and y components ..... I really don't understand
Syamthanda Reply
hey , can you please explain oxidation reaction & redox ?
Boitumelo Reply
hey , can you please explain oxidation reaction and redox ?
Boitumelo
for grade 12 or grade 11?
Sibulele
the value of V1 and V2
Tumelo Reply
advantages of electrons in a circuit
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we're do you find electromagnetism past papers
Ntombifuthi
what a normal force
Tholulwazi Reply
it is the force or component of the force that the surface exert on an object incontact with it and which acts perpendicular to the surface
Sihle
what is physics?
Petrus Reply
what is the half reaction of Potassium and chlorine
Anna Reply
how to calculate coefficient of static friction
Lisa Reply
how to calculate static friction
Lisa
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Tumelo
how to calculate the magnitude of horizontal component of the applied force
Mogano
How to calculate force
Monambi
a structure of a thermocouple used to measure inner temperature
Anna Reply
a fixed gas of a mass is held at standard pressure temperature of 15 degrees Celsius .Calculate the temperature of the gas in Celsius if the pressure is changed to 2×10 to the power 4
Amahle Reply
How is energy being used in bonding?
Raymond Reply
what is acceleration
Syamthanda Reply
a rate of change in velocity of an object whith respect to time
Khuthadzo
how can we find the moment of torque of a circular object
Kidist
Acceleration is a rate of change in velocity.
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t =r×f
Khuthadzo
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Precious Reply
hi
Shongi
hi
Leago
use fnet method. how many obects are being calculated ?
Khuthadzo
khuthadzo hii
Hulisani
how to calculate acceleration and tension force
Lungile Reply
you use Fnet equals ma , newtoms second law formula
Masego
please help me with vectors in two dimensions
Mulaudzi Reply
how to calculate normal force
Mulaudzi
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Source:  OpenStax, Physics for k-12. OpenStax CNX. Sep 07, 2009 Download for free at http://cnx.org/content/col10322/1.175
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