SPEED AND VELOCITY Class 9 Notes | EduRev

Class 9 : SPEED AND VELOCITY Class 9 Notes | EduRev

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SPEED

Speed is the rate of change of distance travelled.Since it has no diretion and it only has unit and magnitude it is a scalar quantity.Its S.I unit is m/s.A fast-moving object has a high speed and covers a relatively large distance in a short amount of time. Contrast this to a slow-moving object that has a low speed; it covers a relatively small amount of distance in the same amount of time. An object with no movement at all has a zero speed.


VELOCITY

Velocity is the rate of change of displacement.Since it has direction,unit,and magnitude it is a vector quantity.Its S.I unit is m/s. If a person in motion wishes to maximize their velocity, then that person must make every effort to maximize the amount that they are displaced from their original position. Every step must go into moving that person further from where he or she started. For certain, the person should never change directions and begin to return to the starting position.


AVERAGE SPEED

Let us consider a practical situation are we able to move around with uniform speed we are not in most cases, we/objects will be in non-uniform motion. Therefore, we describe the rate of motion of such objects in terms of their average speed. The average speed of an object is obtained by dividing the total distance travelled by the total time taken. That is, average speed = Total distance travelled / Total time taken

eg:

An object travels 16 m in 4 s and then another 16 m in 2 s. What is the average speed of the object?

Solution: Total distance travelled by the object = 16 m + 16 m = 32 m Total time taken = 4 s + 2 s = 6 s

Average speed = Total distance travelled /Total time taken

= 32 m 6 s = 5.33 m s–1

Therefore, the average speed of the object is 5.33 m s–1.


AVERAGE VELOCITY

In case the velocity of the object is changing at a uniform rate, then average velocity is given by the arithmetic mean of initial velocity and final velocity for a given period of time. That is, average velocity = initial velocity +finalvelocity / 2

Mathematically, v = u+v / 2

 where v is the average velocity, u is the initial velocity and v is the final velocity of the object

eg:


 

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