SPEED AND VELOCITY CLASS IX Speed speed of

§ Speed : speed of an object is define as the distance traveled by

Eg. A car is moving in a crowded area. 3. Average speed: average speed

Velicity: velocity of a body is define as the displacement of body per unit

Average velocity: average velocity is defined as the ratio of the total displacement of

1. Differentiate between speed and velocity. 2. Name the device used to measure the

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SPEED AND VELOCITY CLASS - IX

§ Speed : speed of an object is define as the distance traveled by it per unit time. I. e. speed of an object tells us how fast an object moves Expression for speed : let distance traveled by an object be S in time t. then Speed = distance / time I. e. v = s/ t Its SI unit is metre/ second and denoted by m/s. It is a scalar physical quantity. Types of speed: 1. Uniform speed : If a moving body covers an equal distance in equal interval of time then the speed of the body is said to be uniform. Eg. Light travels in air with a constant speed. 2. non- uniform speed or variable speed: if body covers unequal distances in equal intervals of time then the speed of body is said to be variable speed

Eg. A car is moving in a crowded area. 3. Average speed: average speed of a body is defined as the ratio of total distance travelled by it to total time taken by it. Average speed = total distance travelled/total time taken Usually buses cars do not move with uniform speed. They move with variable speed in such cases we have to find average speed. 4. The speed of an object at any instant during its motion is called Instantaneous speed. The instrument speedometer fitted on dash board of The vehicles indicates the instantaneous speed.

Velicity: velocity of a body is define as the displacement of body per unit time if the displacement of a body is S in time t. then, Velocity = displacement/ time or v = s/ t. Its SI unit is m/s. and it is a vector quantity. Types of velocity: 1. uniform velocity: velocity of a body is said to be uniform if it covers equal displacement in equal interval of time. 2. Non-uniform velocity: velocity of a body is said to be variable if it covers unequal displacements in equal intervals of time.

Average velocity: average velocity is defined as the ratio of the total displacement of the body to total time taken. Average velocity = total displacement of body / total time taken Note: velocity of the body can be changed either by Changing the speed of the body and keeping the direction of motion same. Changing the direction of motion of the body but keeping the speed same. Changing both speed and direction of motion. Special case : speed of a body and magnitude of velocity of a body are equal if the body moves in a straight line in one direction. 3. § §

1. Differentiate between speed and velocity. 2. Name the device used to measure the instantaneous speed. 3. Name the physical quantity which tells us how fast an object moves. 4. 5. 6. 7. Under what conditions is the magnitude of the average velocity of an object equal to its average speed? How we can change the velocity of an object? define Variable velocity. If a car covers 500 m in 1 min and another 500 m in 2 min. find average speed of the car.