During which type of motion of an object along a straight line does its velocity remain constant with time?

Introduction / Context:
Kinematics distinguishes between different types of motion based on how position, velocity and acceleration change with time. When we say that velocity remains constant, we mean both speed and direction do not change. For motion along a straight line, direction is fixed, so constant velocity means constant speed in that direction. This question asks which named type of motion along a straight line corresponds to constant velocity.

Given Data / Assumptions:

• The object moves along a straight line path.
• We compare various descriptive terms for motion.
• Velocity is considered as a vector quantity, including both magnitude and direction.
• Constant velocity means no change in speed or direction with time.

Concept / Approach:
Uniform motion along a straight line is defined as motion in which the object covers equal displacements in equal intervals of time, no matter how small those intervals are. This is equivalent to saying that its velocity is constant. Linear motion alone merely indicates straight line motion, not whether speed is constant or changing. Translational motion is a general term for any motion in which all parts of a body move in the same way and can still be accelerated. Equilibrium refers to net force being zero; in a straight line, that condition implies constant velocity, but the safest and most precise term among the options is uniform motion.

Step-by-Step Solution:
Step 1: Recall that velocity remains constant only when there is no acceleration acting on the object. Step 2: For straight line motion, this means the object covers equal distances in equal time intervals. Step 3: This behaviour matches the definition of uniform motion along a straight line. Step 4: Linear motion simply describes the path as straight but does not specify whether speed is uniform. Step 5: Translational motion is broader and may include accelerating or decelerating motion. Step 6: Therefore, the correct term for straight line motion with constant velocity is uniform motion.

Verification / Alternative check:
If you plot position versus time for uniform motion, you obtain a straight line graph with constant slope. The slope represents velocity, and its constancy shows that velocity is unchanging. In contrast, non uniform motion yields curved position time graphs, indicating changing velocity. This graphical perspective confirms that uniform motion is the appropriate description for constant velocity along a straight line.

Why Other Options Are Wrong:
Linear motion of any kind: Includes both uniform and accelerated motion; it does not guarantee constant velocity.

Translational motion with changing speed: By definition involves changing velocity, so it contradicts the idea of constant velocity.

Motion in equilibrium only: While dynamic equilibrium can imply constant velocity, the question asks for a standard term for the motion itself, which is best described as uniform motion.

Common Pitfalls:
Students sometimes confuse the words linear and uniform, thinking that a straight path automatically means constant speed. In reality, a car can speed up or slow down while still moving straight. The key word that signals constant velocity is uniform. Always link uniform motion with the idea of equal distances in equal times and zero acceleration.

Final Answer:
Velocity remains constant during uniform motion along a straight line.