Introduction
An object that keeps changing its position for its surroundings is said to be in motion. When the object covers an equal distance in the same amount of time in one direction, it is said to be in uniform motion. If this object covers unequal distances in the same time intervals, it is said to be in non-uniform motion. In this blog, let us further understand the concept of uniform and non-uniform motion.
Uniform Motion
By definition, a body is said to be in uniform motion if it keeps moving with constant velocity.
For example, a cyclist covers a distance of 5 km in one hour, 10 km at the end of the second hour, and 15 km at the end of the third hour is said to be in uniform motion because he is covering 5 km every hour.
Features of Uniform Motion
Uniform motion has some typical features, which are as follows:
- For a uniform motion in a straight line in a particular direction, the amount of displacement equals the distance covered by the moving object.
- Velocity in uniform motion is independent of the time interval.
- Velocity in uniform motion does not depend on the choice of origin.
- If the object moves to the right of the origin, then the velocity is considered positive. If the object moves to the left, then the velocity is negative.
- The value of average and instantaneous velocity is equal for uniform motion.
- A body needs no force to be in uniform motion.
Graphical Representation of Uniform Motion
(a) Displacement-Time Graph for an Object in Uniform Motion
The slope of a displacement-time graph gives the velocity of the moving object.
(i) If an object is in uniform motion along a straight line path, starting from the origin O.
Velocity here is considered positive and constant. In this case, the graph obtained is a straight line originating at point O representing the origin, and moves with a gentle slope.
(ii) If an object moves in a straight line path starting from a positive position.
In this case, the graph obtained originates at a point on X-axis and slopes down towards the Y-axis.
b). Velocity-Time Graph for an Object in Uniform Motion
The velocity-time graph for a uniform motion in a straight line is a straight line parallel to the Y-axis of the graph. The area under the Velocity-time graph gives the displacement of the moving object.
Non-Uniform Motion
By definition, a body is said to be in non-uniform motion if it moves with different velocities. For example, a car moving 30 km in the first hour travels only 20 km in the next hour and again 30 km in the third hour.
Features of Non-Uniform Motion
- In non-uniform motion, the distance travelled by the object may not be equal to the distance.
- The velocity of an object in non-uniform motion depends on the time interval.
In non-uniform motion, two forms of velocity can be considered:
Variable Velocity: An object is said to move with variable velocity if its speed or its direction of motion or both change with time,
Average velocity: An object’s average velocity is considered the ratio of total displacement to the total time taken to cover it. It can be considered that uniform velocity with which an object will cover the same displacement in a given time interval as it does with its actual variable velocity during the given time interval.
Graphical Representation of Non-Uniform Motion
a) Position- Time Graph for non-uniform Motion
If an object travels straight with a non-uniform velocity, its graph will be represented as a curved line. The object’s average velocity over a given time interval will equal the slope of the line formed by joining two points on the graph that denote the beginning and end of the time interval. The slope of the tangent to the position time graph gives the object’s instantaneous velocity.
b) Velocity- Time Graph for Non-Uniform Motion
The velocity-time graph for non-uniform motion is a curved line. The area covered under this graph gives the distance covered by the object.
Difference Between Uniform and Non-Uniform Motion
Uniform Motion |
Non-Uniform Motion |
|---|---|
| A body in uniform motion traverses an equal distance in equal time intervals. | A body in non-uniform motion travels unequal distances in equal intervals of time. |
| The velocity of a body in uniform motion remains constant. | The velocity of a body in non-uniform motion keeps changing. |
| Acceleration in uniform motion is zero. | Acceleration in non-uniform motion is not zero. |
| The graph is a straight line. | The graph is not a straight line. |
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It is the limit of average velocity as the time interval around a given time tends to be zero, i.e. it becomes extremely small. Velocity is considered negative when the object moves to the left of the origin or the point of reference for the observer. The position-time graph for uniform motion cannot be a straight line parallel to the position axis, as it will show indefinite velocity, which is impossible. We get negative acceleration when the velocity of an object decreases at a constant rate. Its rate of change per square unit of time is called negative acceleration or retardation.”
What is instantaneous velocity?
When can velocity be considered negative?
Can the position-time graph for a uniform motion be parallel to the position axis?
What is negative acceleration?
