This document provides an overview of motion in a straight line, including definitions of key concepts like position, velocity, acceleration, and different types of motion. It discusses uniform and non-uniform motion, average and instantaneous speed and velocity, and introduces the kinematic equations for uniformly accelerated motion. Key points covered include defining rectilinear, circular and oscillatory motion, position as a coordinate, frames of reference, and formulas for average velocity, acceleration, and solving problems involving motion under constant acceleration.

1. MOTION IN A
STRAIGHT LINE
CLASS XI PHYSICS
CHAPTER 2

2. MOTION
Motion :- If the position of an object is
continuously changing w.r.t. its surrounding,
then it is said to be in the state of motion.
Motion is a change in position of an object with
time. It is common to everything in the
universe.
Example - We see that a train is moving on rails , the walking man,
the crawling insect, water flowing down a dam, etc.

4. Types of motion
❖ Rectilinear Motion- The motion in which a particle moves
along a straight line is called rectilinear motion.
Example - Motion of a sliding body on an inclined plane.
❖ Circular Motion- The motion in which a particle moves in a
circular path is called circular motion.
Example - A string whirled in a circular loop.
❖ Oscillatory Motion- The motion in which a particle moves to
and fro about a given point is known as oscillatory motion.
Example - Simple pendulum.

5. POSITION, FRAME OF REFERENCE,
PATH LENGTH AND DISPLACEMENT
➢ Position - It is defined as the point where an object
is situated. Position can be determined by the
coordinate axis that is, marked in units of length and
that has positive and negative direction.
Example - If an object is situated at -1m then
minus sign indicates that the position has negative
direction but if the object at 0m position then it will
be said to be at rest.
➢ Frame of Reference - The fixed point or place with
respect to which the position velocity and
acceleration of a body is measured is known as
frame of reference.

6. Frame of reference are of two types
1) Inertial frame of reference :- Any frame of reference
which is either at rest or moving with uniform velocity is
called Inertial frame of reference.
Example :- A plane moving on a horizontal track with
constant is an inertial frame reference.
2) Non-Inertial Frame of reference :- A frame of reference
which is accelerated is called non-inertial frame of
reference.
Example :- Body falling down under the force of gravity.

7. ➢Path length and Distance :- The path covered by a object in a
given time interval, is called Path length or Distance.
Example :- Suppose an object moves along x axis to a distance
of 100m from the origin in time ‘t’. Then the path length is
100m.
➢Displacement :- The shortest distance from the initial
position to the final position of the particle is called
displacement.
Displacement = x2 – x1

8. VELOCITY & SPEED
❑ Velocity :- The rate of change in position or displacement of an
object with time is called the velocity of that object.
✓Uniform Velocity :- An object could have uniform velocity if it
covers equal displacement in equal interval of time.
✓ Non-Uniform Velocity :- A body said to be move with non-
uniform velocity if it covers unequal displacement in equal
interval of time.

9. Comparisons

10. ➢Speed :- The distance travelled by a body per unit time is called
speed of a body.
1) Uniform speed :- A particle or a body is said to be moving with
uniform speed if it covers equal distances in equal interval of
time.
2) Variable speed :- A particle or a body is said to be moving with
variable speed if it covers unequal distance in equal interval of
time.

12. AVERAGE VELOCITY & AVERAGE
SPEED
❖Average Velocity :- Average velocity is defined as ratio of total
Displacement to the total time taken.
❖Average Speed :- Average speed is defined as the ratio of Total
distance travelled to the Total time taken.

13. INSTANTANEOUS VELOCITY &
INSTANTANEOUS SPEED
➢Instantaneous Velocity :- Instantaneous of a particle is defined
as the velocity of a particle at any instant of time.
➢Instantaneous Speed :- When a body is moving with variable
speed then the speed of a body at any instant of time is called
instantaneous speed.

14. Q.A car is moving along a straight line, say OP in
Fig. 3.1. It moves from O to P in 18 s and returns
from P to Q in 6.0 s. What are the average velocity
and average speed of the car in going (a) from O to P
? and (b) from O to P and back to Q ?

15. Q. The position of an object moving along x-axis is
given by x = a + bt2 where a = 8.5 m, b = 2.5 m s–2
and t is measured in seconds. What is its velocity
at t = 0 s and t = 2.0 s. What is the average
velocity between t = 2.0 s and t = 4.0 s ?

17. ACCELERATION
➢Acceleration :- The rate of change of velocity of an object with
time is called the acceleration of a body.

18. ❑ Average Acceleration :- Average acceleration is defined as the
change in velocity of a body divided by total time taken.
❑ Instantaneous acceleration :- It is defined as the acceleration of
an object at any instant of time during its motion.
❑ Uniform acceleration :- The motion of a body whose
acceleration is constant is known as uniformly accelerated
motion.
❑ Non-Uniform acceleration :- The motion of an object having
variable acceleration is known as non-uniform accelerated
motion.

20. KINEMATIC EQUATION FOR
UNIFORMLY ACCELERATED MOTION.

21. QUICK RECAP OF BASIC EQUATIONS
AND UNITS