CBSE Physics Class IX (9th) Motion Part 2

CBSE Physics Class IX (9th) Motion Part 2

Uniform and Non-uniform Motion

Uniform Motion: When a moving body always travels equal distance in equal interval of time, then its motion is called uniform motion.

Example: If a car covered 5km distance in every hour, then its motion is called uniform motion.

Non-uniform motion: When a body travels different distances in equal interval of time, then its motion is called non-uniform motion.

Example: It a covered 5km in first hour then 10 km in second hour then 12 km in third hour. So, its motion is called non-uniform motion.

Speed:

The distance traversed by a body in unit time is called its speed.

This distance can be traversed in straight line or in curved path.

If ‘S’ distance traversed by a car in time ‘t’ then,

Distance traversed by the car in unit time = S/t

Therefore, Speed of the car = S/t

i.e. Speed = traversed distance/ time

                  = S/t  ( where s= distance, t = time)

Speed is scalar quantity.

C.G.S and S.I unit of speed is cm/sec and m/sec respectively.

Average Speed:

For a given interval of time, the ration of the distance traversed and interval of time elapsed is the average speed.

Example: If an object travels x1 distance in time t1, x2 distance in time t2 and x3 distance in time t3

Then total distance traversed = x1+x2+x3

          Total time elapse             = t1+t2+t3

Average speed =(Total distance traversed/ total time

                                                                               elapsed)

                             = (x1+x2+x3)/ (t1+t2+t3)

C.G.S and S.I unit of average speed are cm/sec and m/sec respectively.

Velocity:

The distance traversed by a body in a particular direction in unit time is called its velocity.

That is , the rate of change of displacement is the velocity of the body.

If ‘S’ be the displacement in time ‘t’

Then displacement in unit time = S/t

Therefore, velocity of the particle = V = S/t

Velocity = Displacement/ Time

Velocity has magnitude and time both. So it is a vector quantity.

C.G.S and S.I unit of velocity are cm/sec and m/sec respectively.

Uniform Velocity and Non-uniform Velocity:

Uniform Velocity: When direction and magnitude of a moving object remain same then its velocity is called uniform velocity.

Non-uniform Velocity: When both direction and magnitude or any one of them change with time then its velocity is called non-uniform speed.

Example: Motion of an object in circular path with uniform speed is non-uniform velocity.

Average Velocity: Average velocity is the total amount of distance from the starting point divided by the amount of time passed to get to the final destination.

                                   Total Displacement(S)  

Average Velocity = ---------------------------------------

                                        Total time (t)

Difference between Speed and Velocity:

Speed	Velocity
1.       The distance covered by an object in unit time is called its speed. 2.       Scalar quantity. 3.       An object having uniform speed, may not have uniform velocity.	1.The distance covered by an object in unit time in a particular direction is called its velocity. 2. Vector quantity. 3. an object having uniform velocity must have uniform speed.

Acceleration:

When an object movers with gradually increasing velocity, the rate of change of velocity with respect to time is called its acceleration.

Acceleration(f) = (change in velocity/ time)

                       = ( Final velocity – initial velocity) / time

Acceleration has both magnitude and direction. So, it is a vector quantity.

C.G.S and S.I unit of acceleration are cm/secᶻ and m/secᶻ respectively.

Uniform Acceleration and Non-uniform Acceleration:

Uniform Acceleration: If the velocity of a moving body changes uniformly in equal interval of time, then the body is said to have uniform acceleration.

Non-uniform Acceleration: When the velocity of the body does not change uniformly in equal interval of time, the acceleration is said to be non-uniform acceleration.

Retardation:

The rate of decrease of velocity with respect to time is called retardation.

Retardation = (decrease in velocity/ time)

CBSE Physics Class IX (9th) Motion Part 2


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