# Rest and Motion

## What is position?

Position is a place where someone or something is located or has been put. Position is a vector quantity because it has direction.

## What is rest?

When an object does not change its position with respect to time, then it is at rest.

With the change of time if an object does not change its position with respect to the surrounding its state is known as resting position. And this state of being static is known to be rest.

## What is motion?

When an object changes its position with time, then it is in motion.

With the change of time if an object changes its position with to the surrounding its state is known to be moving. And this state of being moving is known to be motion.

## What is absolute motion?

Motion of an object with respect to an absolute resting reference point is known as absolute motion.

### What is reference Point?

The firm object which is used to determine the position, rest, or motion of other objects is known as the reference point.

## What is reference frame?

The point with respect to which the displacement of an object is measured is called the reference point.

Fixed object with respect to which the position, rest and motion of another object find out, is known as a reference frame.

## All rest and motion of this universe is relative - Explain.

A body is said to be in absolutely rest when it is in rest with respect to an absolutely rest object. Similarly absolute motion of a body is its motion with respect to a reference object absolutely ar rest. But in this universe it is not possible to get a reference object which is at absolute rest. Since the earth is continuously moving round the sun, while the sun itself is moving along the galaxy with its planet and satellites. Thus when we say that a body is at rest or in motion, we mean it is to be so with respect to a body apparently ar rest. So, we can say that in this universe all rest and all motion are relative.

No rest or no motion is absolute.

## Difference between rest and motion

The difference between rest and motion are given below:

a) The velocity of all the particles in rest is zero.

The velocity of all the particles in motion is greater than zero.

b) The rest of a body is impossible to determine.

The motion of a body can be expressed by different quantity, like-displacement, speed, velocity, etc.

c) No body is in absolute rest.

Every particle is in motion.

## More Explanation

We don't have any problems in understanding which object is at rest or in motion around us. We observe by our eyes in such a way that when anything moves slightly, we can recognize it very quickly.

So, we can realize very amazingly what the terms rest and motion mean.

But in physics, it is not sufficient only to realize rather it has to be well defined. To definite it, we can say briefly, when an object does not change its position with respect to time, then it is at rest. And when an object changes it position with time, then it is in motion. Now we need to explain the term 'position' properly.

In our daily conversation we use the word 'position' in different ways, but in physics the word 'position' has definite meaning. If you are asked, where is the position of your school and if your answer is 'Jhiltuli', your answer is correct but the position of your school remains unknown. If you reply, your school is 1 kilometer far from the gate of your residence; the position of your school is still unknown.

Though the position of the gate of your residence is known to us, yet we cannot tell exactly in which direction the school is situated at a distance of 1 kilometer from the gate. But if you say the school is situated east from the gate of your residence, only then we will know the exact position of your school.

That is to know the position of the school; we have to know both the distance and the direction definitely. Not only this, this distance and direction and direction has to be specified from the position of a reference point. In the case of your school, the gate of your residence was the reference point or origin.

Instead of your residence gate, the reference point might be a bus stop or a shopping mall. Then definitely both the position and the direction would have different values, but we can specify the position of any object, it has to be mentioned with respect to a reference point.

This reference point is not an absolute one; we can conveniently choose any point as reference point or origin.

Now the question is, to specify the position of an object, is it necessary for the reference point or origin to be a still point? Let us think, in front of you a person is sitting still on a chair. If we consider the chair as the reference point or origin, then we can firmly say, the position of your friend is not changing.

If it happens that actually you are sitting in a moving train, what will it then be?

A man outside of the train standing on the station will say, you and your friend are both in motion, nobody is at rest. Then whose statement is true?

Your statement or of the man standing in the station. In fact, both are correct! The reason is - if the reference point or the origin moves at a uniform velocity, then we cannot tell firmly whether the reference point is moving at a uniform velocity, then we cannot or actually it is at rest and all other things are moving at uniform velocity in the opposite direction.

Therefore we can say, if an object changes its position with respect to an origin, then the object is in motion with respect to that origin. It is not our headache whether the origin is at rest or moving at uniform velocity. This is not important since every motion is relative.

Not only this, if we want to search out an absolute rest reference point, we will be in trouble. If we consider anything on the surface of the earth as origin one can object, earth is not stationary rather it is rotating about its own axis, so everything on its surface is also rotating.

Alternatively we can say, the center of the earth is the origin. Then someone else can come up with the objection that the centre of the earth is not is not stationary, it revolves around the sun. Then we can say more intelligently, the centre of the sun must be the origin!

Then another person can confidently say that the sun is also not stationary it is also revolving around the centre of our galaxy. Surely you are feeling that no one can dare to say, the centre of our galaxy is the origin!

Who can say that the galaxy and the universe are stationary?

Not only this, if the centre of the galaxy is considered as the origin to describe any position on the surface, do you realize the extent of complexities that may arise?

In fact, we don't need such type of complexities, for our purpose we can consider any point as the origin, which seems stationary to us. In this case we have to mentioned all the measurements are done with respect to this origin. In this way scientists have done all the measurements starting from the nucleus of an atom to the satellites launched in space, with no problems what so ever!

No Comment