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Physics - 11 Complete Syllabus Notes

Chapter 3 - Kinemetics

The branch of mechanics which deals with the study of motion of the object without considering the cause of motion is called kinematics.

Some important terms:

Distance: The length of the path travelled by an object is called distance. It is a scalar quantity. Its S.I unit is meter(m) and C.G.S unit is (cm). Its dimensional formula is [L]

Displacement: The shortest distance between initial position and final position of an object is called displacement. It is a vector quantity. Its S.I unit is meter(m) and C.G.S unit is (cm). Its dimensional formula is [L].
The relation between distance and displacement is
Distance $\geq$ Displacement

Speed: The distance travelled by an object per unit time is called speed. i.e $speed=\frac{Distance&space;&space;Travelled&space;}{Time&space;taken}$
It is scalar quantity. Its S.I unit is m/s and cgs unit is cm s-1. Its dimensional formula is [M0 L T-1]

Velocity: The rate of change of displacement of an object is called velocity. i.e. velocity = (displacement) / Time
It is a vector quantity =. Its S.I unit is m/s and CGS unit is cm s-1. Its dimensional formula is [M0LT-1]

Uniform Velocity: If there is equal displacement of an object in equal interval of time then the object is moving with uniform velocity.

Non- Uniform Velocity: If the object is moving with variable velocity (either change in magnitude or change in direction or both) then the object is moving with non- uniform velocity.

Average Velocity: The ratio of displacement (change in position) and a time taken for displacement is called average velocity. i.e. Average velocity = $\frac{x_{2}-x_{1}}{t_{2}-t_{1}}$
Vav = $\frac{\Delta&space;x}{\Delta&space;t}$
Also, Vav = (u+v) / 2

Instantenous Velocity: The rate of change of displacement of a object is called instantenous velocity or the velocity of an object at particular instant is called instantenous velocity . The velocity measured by the speedometer in vehicle is instentenous velocity.
V = ds / dt

Acceleration: The rate of change of velocity is called Acceleration.
i.e. Acceleration = (change in velocity) / Time taken
It is a vector quantity. Its SI unit is ms -1 and CGS unit cm s-2. Its dimensional formula is [LT-2]

also,
a = (v - u) / t 
Special Cases

i) If v > u (Accelerating)
a will be positive (speeding up)

ii) If v = u (zero accelerating)
a will be zero (constent speed)

iii) If v < u (De accelerating )
a will be negative (speeding down)

Uniform Acceleration: If there is equal change in velocity of object in equal interval of time then the object is moving with uniform acceleration.

Non-Uniform Acceleration: If object is moving with variable acceleration (either change in magnitude or change in direction or both ) , then the object is moving with non - uniform acceleration .

Average Acceleration: The ration of change in velocity and time interval for change in velocity is called average acceleration.
     i.e. aav = (v2 - v1) / (t2 - t1)
Instantenous Aceleration: The rate of change of velocity of an object with respect to time is called instantenous acceleration.
a = dv / dt

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