Uniform Motion

Uniform motion describes movement at constant velocity. Distance, speed, and time are related by d = vt.

What is Uniform Motion?

Uniform motion occurs when an object moves in a straight line at constant speed — no acceleration.

Velocity-time graph for uniform motion (constant v)

Displacement in Uniform Motion

s = v \cdot t

s = displacement (m), v = velocity (m/s), t = time (s)

Average Speed vs Velocity

Speed is a scalar (magnitude only).
Velocity is a vector (magnitude + direction).

For uniform motion, average speed = instantaneous speed = $v$ .

A car travels at 60 km/h for 2.5 hours. How far does it go?

$s = 60 \times 2.5 = 150 \text{ km}$

Real world: Highway cruise control

A car on the motorway uses cruise control set to 120 km/h. For 45 minutes (= 0.75 h) the speed is perfectly constant. Distance covered:

$s = 120 \times 0.75 = 90 \text{ km}$

This is the ideal model of uniform motion — constant speed, straight line, zero acceleration.

Real world: Moving walkway at an airport

An airport travelator moves passengers at a constant 1.4 m/s. A passenger stands still on it for 50 seconds. Distance carried:

$s = 1.4 \times 50 = 70 \text{ m}$

Real world: Boat crossing a calm river

A rowing boat moves at a steady 2 m/s in still water. To cross a 120 m wide lake it takes:

$t = \dfrac{120}{2} = 60 \text{ s}$

Tip

Where do you see this in real life? Conveyor belts in supermarkets, escalators, and satellite orbits all approximate uniform motion. In reality, perfectly constant speed is rare — but it is a useful starting model for many calculations.

Practice Problems

A train moves at 90 km/h. How long does it take to travel 270 km?

Show answer

t = s/v = 270/90 = 3 hours

A runner covers 400 m in 50 s. What is their average speed?

Show answer

v = s/t = 400/50 = 8 m/s