In which type of motion of a body does its velocity change with time instead of remaining constant as it moves?

Introduction / Context:
Describing motion accurately is a central part of mechanics. Two important categories of motion are uniform and non-uniform motion. These categories describe how the speed or velocity of an object behaves over time. This question focuses on recognising which term is used when the velocity of a moving body changes as time passes.

Given Data / Assumptions:

• The body is in motion along some path.
• We are told that its velocity varies with time.
• We want the standard term used in physics for such motion.

Concept / Approach:
Uniform motion is defined as motion in which an object covers equal distances in equal intervals of time, implying constant speed and, in a straight line, constant velocity. Non-uniform motion, on the other hand, is motion in which either the speed or direction (or both) of the object change with time. If the velocity is varying, the motion cannot be uniform and must be classified as non-uniform. Terms like linear motion and equilibrium motion describe other aspects and do not directly refer to whether velocity is constant or changing.

Step-by-Step Solution:
Step 1: Note that the body velocity is changing with time. Step 2: Recall that in uniform motion, velocity remains constant over time, so this description does not fit. Step 3: By definition, non-uniform motion is motion with changing speed or direction, meaning velocity is not constant. Step 4: Conclude that the correct classification is non-uniform motion and select that option.

Verification / Alternative check:
Consider a car whose speedometer reading increases from 30 km/h to 50 km/h over a few seconds. Its velocity is clearly changing, so its motion is non-uniform. In contrast, a train moving steadily at 60 km/h on a straight track would be in uniform motion. This comparison reinforces that the key requirement for uniform motion is constant velocity, which is not satisfied in the question.

Why Other Options Are Wrong:

• Uniform motion: This refers to motion with constant velocity, which is the opposite of the situation described.
• Linear motion: This simply indicates motion along a straight line and does not specify whether velocity is constant or changing.
• Equilibrium motion: This is not a standard category for motion in basic mechanics and does not correctly describe changing velocity.

Common Pitfalls:
Students sometimes think any motion along a straight line must be uniform, which is not true. A car speeding up or slowing down along a straight road is still undergoing non-uniform motion because its velocity is changing. Confusing path shape (linear or curved) with time variation of velocity is a frequent source of error. Always focus on whether the velocity magnitude and direction remain constant over equal time intervals.

Final Answer:
The correct description is non-uniform motion.