# Class 11 Physics Chapter 3 Notes Motion In A Straight Line

## Motion in a Straight Line

A body is said to be in motion if it changes its position with respect to time.

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### Types of Rectilinear/Linear Motion

The Rectilinear Motion or linear motion can be of two types:

1. Non-Uniform linear motion with non-zero acceleration orÂ variable velocity
2. Uniform linear motion with zero acceleration or constant velocity

The simplest type of one-dimensional motion is Linear motion. As perÂ Newtonâ€™s first law of motion, an object will either be in rest or continue to move in a straight line with a uniform velocity unless and until an external force is applied to it.

Linear motion is often mistaken for general motion. Linear motion is a one-dimensional motion but in general, the motion has both magnitude and direction, i.e. an objectâ€™s position and velocity are described inÂ vector quantities.

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### Uniform Motion in a Straight Line

A body is said to be in a uniform motion if it travels in a straight line covering equal distances in equal intervals of time. A body is said to have uniform acceleration if the rate of change of its velocity remains constant.

The ball covers equal distances in equal intervals of time

Example:

If a car travels at a speed of 60 km/hour then it will cover a distance of 1 km/minute. In this sense, the motion of car acceleration is uniform.

#### For More Information On Motion in One Dimension, Watch The Below Video:

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### Non-uniform Motion in a Straight Line

A body is said to have a non-uniform motion when the velocity of a body changes by unequal amounts in equal intervals of time. While in movement, the rate of change of its velocity changes at different points of time.

Example:

A boy kicking a football. It might cover 4 meters in the first attempt, 6 meters in the second change, 9 meters in the third attempt and so on as per the velocity exerted by the boy.

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### Path Length

The path length is the total length of the path that has to be traversed by the object.

### Displacement

Displacement is the change in position of a body. The magnitude of displacement between the same points is proportional to the path length.

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### Uniform Motion

When the displacement of an object is equal in equal time intervals, the motion is said to be uniform, else it is referred to as non-uniform.

### Average Speed

Average speed is referred to the ratio between the total path length traversed to the time taken.

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### Instantaneous Velocity

It is the velocity when the limit of the average velocity has an indefinitely smaller interval of time.

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### Average Acceleration

It is the change in velocity corresponding to the time interval with in which the change has accelerated.

### Important Questions

1. In which of the following examples of motion, can the body be considered approximately a point object:
• (a) a tumbling beaker that has slipped off the edge of a table
• (b) a monkey sitting on top of a man cycling smoothly on a circular track.
• (c) a railway carriage moving without jerks between two stations.(d)a spinning cricket ball that turns sharply on hitting the ground
1. The position-time (x-t) graphs for two children A and B returning from their school O to their homes P and Q respectively are shown in Fig. 3.19. Choose the correct entries in the brackets below ;
• (a) (A/B) lives closer to the school than (B/A)
• (b) (A/B) overtakes (B/A) on the road (once/twice)
• (c) (A/B) walks faster than (B/A)
• (d) A and B reach home at the (same/different) time
• (e) (A/B) starts from the school earlier than (B/A)

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## Frequently asked Questions on CBSE Class 11 Physics Notes Chapter 3: Motion in a Straight Line

### What is difference between 1D and 2D motion?

1D motion means motion in One dimension. That is the body moves only in one axis either x y or Z. Or simply it moves only linearly. Whereas 2D motion involves motion which is defined as the combination between two axes.

### What is non-uniform motion?

Non-uniform motion is the motion of an object wherein the object moves at different speeds and does not cover the same distance at equal time intervals.

### What is â€˜Accelerationâ€™?

The rate at which velocity changes with time, in terms of both speed and direction is called as acceleration.