Uniform Motion
Uniform motion is motion in which an object travels equal distances in equal intervals of time along a straight line, meaning its velocity is constant and its acceleration is zero. It is governed by Newton's first law (the law of inertia): in the absence of a net external force, a body in motion continues at constant velocity. The position-time graph for uniform motion is a straight line with constant slope.
Key Formula
x = x0 + v × t
LaTeX: x = x_0 + vt
| Symbol | Meaning | Unit |
|---|---|---|
| x | Position at time t | m |
| x₀ | Initial position | m |
| v | Constant velocity | m/s |
| t | Time elapsed | s |
Worked Example
Problem
A boat moves with a constant velocity of 5 m/s due east. If it starts at a position of 20 m from the dock, where will it be after 12 seconds?
Solution
Step 1: Identify values: x₀ = 20 m, v = 5 m/s, t = 12 s. Step 2: Apply uniform-motion equation: x = x₀ + vt = 20 + (5 × 12) = 20 + 60 = 80 m.
Answer
The boat will be 80 m east of the dock after 12 seconds.
Characteristics of uniform vs. non-uniform motion
| Feature | Uniform Motion | Non-Uniform Motion |
|---|---|---|
| Velocity | Constant | Changes with time |
| Acceleration | Zero | Non-zero |
| Position-time graph | Straight line | Curved line |
| Velocity-time graph | Horizontal line | Sloped or curved |
| Net force | Zero | Non-zero |
| Example | Train on straight track at constant speed | Car accelerating from traffic light |
Interactive Tools
Wikimedia Commons, CC BY-SA
Related Terms
Velocity
Velocity is the rate of change of displacement with respect to time, making it a vector quantity with both magnitude (speed) and direction. Average velocity equals total displacement divided by total time, while instantaneous velocity is the derivative of position with respect to time. Velocity is central to Newton's laws and is measured in metres per second (m/s).
Acceleration
Acceleration is the rate of change of velocity with respect to time, and is a vector quantity. An object accelerates whenever its speed changes, its direction changes, or both simultaneously. Acceleration is caused by a net force (Newton's second law) and is measured in metres per second squared (m/s²).
Position
Position is the location of an object in space relative to a chosen reference point, described by a set of coordinates. It is a fundamental concept in mechanics because all motion is defined as a change in position over time. In one dimension, position is typically denoted by x and measured in metres from the origin.
From Latin "uniformis" — "uni-" (one) + "forma" (form, shape) — meaning having one constant form throughout. The term was used in medieval natural philosophy and formalised by Galileo Galilei in the early 17th century.