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Motion in Straight Line

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Physics Part I

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12
Explain clearly, with examples, the distinction between :
(a) magnitude of displacement (sometimes called distance) over an interval of time,
and the total length of path covered by a particle over the same interval

The magnitude of displacement over an interval of time is the shortest distance (which is a straight line) between the initial and final positions of the particle.

The actual path length covered by the particle in a given interval of time is the total length of the path covered by the particle. 

Consider, for example, a particle moves from point A to point B and then, comes back to a point, C taking a total time t. 

Displacement of the particle = AC 

Total path length = AB + BC

Magnitude of displacement can never be greater than the total path length. However, in some cases, both quantities are equal to each other.


What is the most essential thing to study the motion of a body?

The most essential thing to study the motion is reference frame. Rest and motion are relative terms. It means that an object in one situation can be in rest but in another situation, the same object will be in motion. 

Is absolute rest or absolute motion possible?

Absolute rest and absolute motion is not possible because there is no point in the universe which is at rest and can be taken as point of reference. The planet Earth is in continuous motion. 

Can a body be always at rest in some frame?

Yes, a body is always at rest in a frame which is fixed with the body itself. 

What is rest?

When an object does not change its position with time, with respect to it's surroundings. In such a case the object is said to be at rest. 

What is motion?

When an object changes it's position with time, with respect to it's surroundings, the object is said to be in motion.