Speed and velocity

Speed tells you how fast something is moving. Think of it as the distance an object covers in a given time. When you travel from Lagos to Ibadan by car, the distance is about 140 kilometres. If you complete this journey in 2 hours, your average speed is 70 kilometres per hour. Speed answers the question: "How much ground did I cover in this time?"

The formula is straightforward: Speed equals distance divided by time. Speed doesn't care about direction—it only measures how quickly you're covering distance. Whether you're driving north or south doesn't change the speed calculation. A motorcycle moving at 60 km/h on a Lagos express way covers 60 kilometres every hour, regardless of which direction it's heading.

Velocity tells you how fast something is moving in a particular direction. Unlike speed, which only cares about how far you travel, velocity measures the actual straight-line distance you cover and in which direction. Think of it this way: if you drive from Lagos to Ibadan, your velocity isn't just about the total distance, but the direct displacement from your starting point to Ibadan, divided by the time taken.

The formula is simple: velocity equals displacement divided by time. Displacement is different from distance because it's the shortest path between two points. So if a student runs around a football field and ends up back at the starting point, the displacement is zero, making the average velocity zero, even though they covered a large distance.

Speed tells you how fast something moves, while velocity includes direction too. Uniform speed means an object covers equal distances in equal time intervals—like a car maintaining 60 km/h on a straight highway from Lagos to Ibadan. Non-uniform speed happens when this changes, such as a danfo bus speeding up and slowing down as it navigates through Lagos traffic.

The same applies to velocity. Uniform velocity means constant speed in one direction. Non-uniform velocity occurs when either the speed changes or the direction changes, or both. For example, a motorcycle travelling at 40 km/h north maintains uniform velocity, but when it turns a corner while keeping the same speed, the velocity becomes non-uniform because direction changed.

The key difference: uniform motion is smooth and predictable, while non-uniform motion is irregular and changing.

A distance-time graph shows how far an object travels over a period of time. The horizontal axis represents time while the vertical axis shows distance covered. The gradient or slope of the line tells you the speed of the object.

When the line is steep, the object moves faster because it covers more distance in less time. A flat horizontal line means the object is stationary—not moving at all. Think of a commercial bus traveling from Lagos to Ibadan: if it moves at constant speed, the graph shows a straight diagonal line. When the bus stops at a checkpoint, the line becomes horizontal.

The key difference from displacement-time graphs is that distance always increases or stays the same; it never decreases. Displacement can decrease because it measures the shortest path from start to finish.