Work and Internal Energy

Work is defined as ” when the force is applied on any object its diplace from one place to another” which has the component of force and displacement both.Work which is a medium or a type of energy transfer from one object to another. When force is applied on an object as a result the object moves or displace from one place to another this is known as work done.The SI unit of work is joule. It is a scalar quantity because its only has magnitude and direction. Its dimensional formula is ML2T-2. The formula of work is

W = Fs cosθ

Where

 F is force

 s is displacement 

Work done are of three types:-

• Positive work 
• Zero work
• Negative work

Work is said to be positive if the direction of displacement or its component is in the same direction in which the force will be applied.

Word done is said to be zero if the displacement is zero whereas the force wil applied.

Work done is said to be negative if the direction of displacement or its components are in the opposite direction in which the force will be applied .

MEANING OF WORK DONE IN PHYSICS

There is no work done if the displacement comes out to be zero, the force is zero and the force and displacement are mutually perpendicular to each other.

Let’s take an example. Suppose you want to push the wall, you start pushing which consumes a lot of energy but the displacement of the wall becomes zero or no movement of the wall shows that your work done is zero.

Work done= component of force in the direction of displacement x magnitude of displacement

W=(F cosθ) x s

W= Fs cosθ

W= F.s vectors

By this we can say that the work done is a dot product of force and displacement vectors.

As mentioned above,

    W= Fs Cosθ

This formula is only used when the work is done by a constant force.

If we talk about the work done by a variable force we have to integrate this formula and then find the work done.

• When θ is greater than 90° work done is negative.
• When θ is less than 90° work done is positive.
• When θ is 0° work done is zero. 

INTERNAL ENERGY

Internal energy is energy within the system which keeps the gains and the losses of the system in its internal state. It is the sum of kinetic energy and potential energy of the system. It does not include the overall kinetic energy of the system as a whole; it includes only the disordered energy associated with a random motion of the molecules of the system.

It is denoted by U and its unit is Joules. It can be altered by raising the temperature or volume. 

Internal energy of a system is a thermodynamics state variable which means its value depends only on the state of existence of the system and not on the path along which that state has been brought about. It simply means that the internal energy of a given mass of a gas depends only on its state described by the specific values of pressure volume and temperature.

Internal energy of an ideal gas is purely kinetic in nature which means, In ideal gas there are no molecular forces of attraction so the gas does not possess intermolecular potential energy . It’s internal energy is just the sum of kinetic energy associated with various random motions of its molecules. Thus the internal energy of an ideal gas is wholly kinetic in nature and depends only on its temperature.

Factors affecting internal energy:

Factors affecting internal energy are:

1. Heat
2. Work

When a closed system receives energy as heat it brings a change in internal energy and increases its internal energy.

For example, placing a cylinder over a whole body the heat energy will flow from the hotter body to the gas due to the temperature difference which in hands will increase the internal energy of the gas.

(Now according to the first law of thermodynamics,

If some heat is supplied to a system which is capable of doing work then the quantity of heat absorbed by the system will be equal to the sum of the increase in its internal energy and external work done by the system on the surroundings.)

We can say that the internal energy can be changed by the work done.

CONCLUSION:

Work is the energy transferred to or from an object via the application of force along a displacement. Its SI unit is joule and its dimensions are ML2T-2.

Internal energy is the energy within the system which keeps the gain and the losses of the system in its internal state. We can also say it is the energy necessary to create or prepare the system in any given internal state.

Internal energy can only be changed by heat and work.

It is the total amount of kinetic and potential energy possessed by the molecules of the body.