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 or variable velocity
2. Uniform linear motion with zero acceleration or constant velocity

The simplest type of one-dimensional motion is Linear motion. As per Newton’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 object’s position and velocity are described in 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.

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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