## What is ‘MOMENT’?

In physics, if the quantity is multiplied by the distance (radial distance) then the quantity will be termed as moment.

We generally know only about moment of inertia, but torque is also a moment which represents moment of force, and angular momentum is the moment of momentum.

Since, the general meaning of moment is ‘at that particular time‘. Similarly in physics the moment provides position depending on the several distance (at that peculiar time).

## Types of Matter OR States of Matter?

Since, our childhood we know there are actually three states of matter that is solid, liquid and gas.

In higher studies, we aware about two more states which are plasma and condensate.

But what we have not noticed is this that why these are called States not Types?

Since, these forms of matter are interchangeable means they can be converted from there one form to another. Therfore, these are known as States.

While the things we get naturally like stones, wood are the types of solid because they are can’t be changed from one genre to another.

So, we are now familiar with the difference inbetween States and Types.

## OPTICAL PATH vs. GEOMETRICAL PATH

Light has different prodigious properties. One of them is that light takes the time which is extremum. It means that the time should be either minimum or maximum.

One example which will help you to imagine the core of concept is of block. Imagine a block and now drop that block in air one time and then in water other time from same height. Now, you can imagine the timing in which the block will touch the ground.

Absolutely, the block will touch ground fatser in air than in water.

Similarly, we can think in case of light. As light will simply pass in air(vaccum) but will show reflection and refraction in water due to which its time changes. This change in time is either maximum or minimum.(Except normal incidence)

And the path it will follow in air is nothing but the geometrical path and the path it will travel in water is the optical path.

We can say simply, the actual path without any liquid (refractive index) is the geometrical path and when the light travels through any medium (liquid) then its path is said to be optical path.

## DOPPLER EFFECT

Simply, the change in FREQUENCY when some noise is moving towards us or away from us. This process is known as the Doppler Effect.

In this concept, we everytime confuse whether we have to add velocities or subtract them.

But this is simple to understand by a minor concept of numerator and denominator.

As like when we have to increase the value, we either add value to numerator or subtract value from denominator. In both cases, the overall value will increase.

Similarly, for decreasing the overall value we either subtract from numerator or add in denominator.

The same case is for velocities, when the noise is coming which implies the sound increases means add velocity to numerator and subtract velocity from denominator.

And, when noise is moving away which implies sound decreases means subtract velocity from numerator and add velocity in denominator.

Hence, this is the candid concept of Doppler Effect which makes it easier to understand.

## DEGREE OF FREEDOM

This topic is mainly for the behaviour of gases.

As, we have different gases such as monatomic, diatomic, and polyatomic. These are decided by their degree of freedom.

As the word ‘freedom’ suggests, the independent bahavior which implies the freedom of these gases.

These degree of freedom are of three types: Translational, Rotational and Vibrational degree of freedom.

For monatomic gases: The translational, rotaional and vibrational degree of freedom are 3, 0 and 0 respectively.

For diatomic gases: The translational, rotaional and vibrational degree of freedom are 3, 2 and 1 respectively.

For polyatomic gases: These are of two types

1. Non- linear triatomic: The translational, rotaional and vibrational degree of freedom are 3, 3 and 3 respectively.

2. Linear triatomic: The translational, rotaional and vibrational degree of freedom are 3, 2 and 4 respectively.

The Vibrational degree of freedom is not considered untill it is mentioned because it depends on the inner molecule heat energy.

So, generally the overall degree of freedom is 3, 5, 5 and 6 for monatomic, diatomic, linear triatomic and non-linear triatomic gases respectively.

## Concept Of Permittivity

‘ε’(Epsilon) is not only a value in electrostatics, but also had a benign physical significance.

Permittivity is the property of any surrounding. This can be easily explained by the example given below:

Suppose we send a signal which has 100% information but our receiver receives only 60% of signal, then where our 40% signal gone?

This remaining signal is absorbed in the surrounding. So, actually this property of surrounding that how much energy does it absorbs from our source, is termed as its PERMITTIVITY.

This permittivity is different for different mediums. In most of the cases our surrounding is vaccum, so we use ε.(Epsilon naught) which has a fixed value.

Hence, this permittivity only defines the property of surrounding in which any charge is placed in electrostatics.

## WORK ENERGY THEOREM

Does this work energy theorem is only the theoretical thing?

No, friends it is not like that.

We have till now studied, that this theorem states that the work done on any body is given by the change in its kinetic energy.

And this theorem is proved by using Newton’s second law.

It can also be easily proved by our simple kinematics. As, we already know by third law of motion which relates inbetween final velocity, initial velocity, acceleration and displacement.

Multiplying by mass M and dividing by 2, we easily gets the Work Energy Theorem.

And, as we know the work done in a moving body stored in it as its kinetic energy. And in simple words this is work energy theorem nothing else. So, imagine a vehicle starting from rest, you will get the net change in kinetic energy equal to the work done.

Hence, the concept of work energy theorem is easily be understood by our above discussion.

## FRICTION IN SPACE

FRICTION is something that limits us for 100% efficiency. What does it mean?

Means we can’t use something with zero percent energy loss. On Earth we have this loss in different ways such as: Humming loss, Air resistance, Heat loss and much more.

But what about space? Do we also suffer from such losses in space also, specially friction force?

So, the answer is YES. The reason is simply this that we all know space is empty, there is nothing. So, by this concept there should be no loss.

But actually it is not like that, space in reality is not empty. There are Fields, there is Light, there are Microscopic particles.

These things also effect the movement. But there effect is count as negligible.

So, the correct information about FRICTION in space is this that actually friction acts in space but we consider it as negligible.

## THE MYSTERY: Speed Of Light

Almost everybody knows the value of c that is 300,000 Km/sec. Means just impossible to even imagine.

On earth, it is not possible for something to achieve the speed of light. But if let us suppose an object moving with c then what’s about the object?

So, the strange thing is this that the object will disappear, but why?

The answer for its invisibility is cleared by the concept of LENGTH CONTRACTION. It provides us a relation between the rest length, its velocity and between speed of light.

By this concept, we get the approximate lenght of an object moving with speed of light as ZERO.

Hence, light is the biggest mystery even now. As, we didn’t get any visible object till now moving with c.