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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:
b) The magnitude of average velocity over an interval of time, and the average speed over the same interval. [Average speed of a particle over an interval of time is
defined as the total path length divided by the time interval].
Show in both (a) and (b) that the second quantity is either greater than or equal to the first. When is the equality sign true ? [For simplicity, consider one-dimensional
motion only.]

Magnitude space of space average space velocity space equals space fraction numerator Magnitude space of space displacement over denominator Time space interval end fraction

For space the space given space particle comma space

Average space velocity space equals space AC over straight t

Average space speed space is space given space by comma space

fraction numerator Total space path space length over denominator time space interval end fraction space equals space fraction numerator AB space plus space BC over denominator straight t end fraction

Since (AB + BC) > AC, average speed is greater than the magnitude of average velocity.

The two quantities will be equal if the particle continues to move along a straight line.


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. 

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 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. 

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. 

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.