KINEMATICS
*rest and Motion are relative terms, nobody can exist in a state of absolute rest or of
absolute motion.
*One dimensional motion:- The motion of an object is said to be one dimensional
motion if only one out of three coordinates specifying the position of the object
change with time. In such a motion an object move along a straight line path.
*Two dimensional motion:- The motion of an object is said to be two dimensional
motion if two out of three coordinates specifying the position of the object change
with time. In such motion the object moves in a plane.
*Three dimensional motion:- The motion is said to be three dimensional motion if all
the three coordinates specifying the position of an object change with respect to time
,in such a motion an object moves in space.
*The magnitude of displacement is less than or equal to the actual distance travelled
by the object in the given time interval.
Displacement ≤ Actual distance
*Speed:- It is rate of change of distance covered by the body with respect to time.
Speed = Distance travelled /time taken
Speed is a scalar quantity .Its unit is meter /sec. and dimensional formula is
[M0L1T-1] .It is positive or zero but never negative.
*Uniform Speed:- If an object covers equal distances in equal intervals of time than
the speed of the moving object is called uniform speed. In this type of motion,
position – time graph is always a straight line.
*Instantaneous speed:-The speed of an object at any particular instant of time is
called instantaneous speed. In this measurement, the time ∆t→0.
15
, K.V. Aizawl
When a body is moving with uniform speed its instantaneous speed = Average
speed = uniform speed.
*Velocity:- The rate of change of position of an object in a particular direction with
respect to time is called velocity. It is equal to the displacement covered by an
object per unit time.
Velocity =Displacement /Time
Velocity is a vector quantity, its SI unit is meter per sec. Its dimensional formula is
[M0L1T-1]. It may be negative, positive or zero.
*When a body moves in a straight line then the average speed and average velocity
are equal.
*Acceleration:- The rate of change of velocity of an object with respect to time is
called its acceleration.
Acceleration = Change in velocity /time taken
It is a vector quantity, Its SI unit is meter/ sec.2 and dimension is [M0L1T-2], It may be
positive ,negative or zero.
*Positive Acceleration:- If the velocity of an object increases with time, its
acceleration is positive .
*Negative Acceleration :-If the velocity of an object decreases with time, its
acceleration is negative . The negative acceleration is also called retardation or
deacceleration.
*Formulas of uniformly accelerated motion along straight line:-
For accelerated motion, For deceleration motion
V = u + at v = u - at
S = ut + 1/2 at2 S = ut - 1/2 at2
V2 =u2+ 2as V2= u2- 2as
Sn = u + a/2(2n- 1) Sn = u - a/2( 2n- 1)
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