If the speed of an object moving along a straight line is constant, its motion is said to be _________.

Introduction / Context:
Describing motion precisely requires clear definitions. One fundamental idea is uniform motion, in which an object moves at a constant speed along a straight path. This question asks you to recall the correct term for motion along a straight line with constant speed, a basic concept in kinematics.

Given Data / Assumptions:

• The object is moving along a straight line, so its direction is fixed.
• The speed of the object remains constant with time.
• No mention is made of oscillation, rotation or changes in direction.
• We need the correct descriptive term from the given options.

Concept / Approach:
Uniform motion is defined as motion in which an object covers equal distances in equal intervals of time in a straight line. This implies a constant speed and unchanging direction, so the velocity is constant in magnitude and direction. Periodic motion refers to motion that repeats itself after equal intervals of time, such as oscillations, which may or may not have constant speed. Circular motion involves movement along a circular path, where direction changes continuously even if speed is constant. Non uniform motion means either speed, direction or both change with time. Therefore, the appropriate term here is uniform motion.

Step-by-Step Solution:
Step 1: Note that the motion is along a straight line, so there is no change in direction.Step 2: The speed is constant, meaning the object covers equal distances in equal time intervals.Step 3: These two conditions together match the definition of uniform motion.Step 4: Periodic motion would require repeating cycles such as oscillations, which are not mentioned.Step 5: Circular motion would involve a curved path; here the path is straight, so circular does not apply.Step 6: Non uniform motion would have variable speed or direction, which contradicts the constant speed stated.Step 7: Conclude that the correct description is uniform motion.

Verification / Alternative check:
Imagine a car moving on a straight highway at exactly 60 km/h with no speed changes and no turns. Over every one minute interval, it travels the same distance, for example one kilometre each minute. This is uniform motion. In contrast, a car moving around a circular track at constant speed has constant speed but changing direction, so its motion is uniform circular motion, not uniform motion along a straight line. The question clearly specifies straight line, reinforcing that uniform motion is the correct description.

Why Other Options Are Wrong:
Periodic motion focuses on repetition in time, such as a pendulum swinging back and forth. It does not necessarily imply constant speed along a straight line. Circular motion implies a curved path, not a straight line as given. Non uniform motion means speed or direction changes over time, which contradicts the condition that speed is constant and direction is fixed.

Common Pitfalls:
Some students may confuse uniform motion with periodic motion because both involve regular patterns. However, uniform motion is about equal distances in equal times, while periodic motion is about repetition of whole cycles in equal times. Others may think that any motion with constant speed is uniform, ignoring direction changes. The definition of uniform motion in simple kinematics includes straight line motion with constant speed.

Final Answer:
If an object moves along a straight line with constant speed, its motion is called uniform motion.