Velocity is a fundamental concept in physics that describes the rate at which an object changes its position. Unlike speed, which only tells us how fast an object is moving, velocity also tells us the direction of that motion. As a vector quantity, velocity provides a complete description of an object's motion.
Velocity () is defined as the rate of change of displacement.
Mathematically, the average velocity is expressed as:
Where:
This is a critical distinction in physics.
| Feature | Speed | Velocity |
|---|---|---|
| Type of Quantity | Scalar | Vector |
| Definition | Rate of change of distance | Rate of change of displacement |
| Direction | Has no direction | Has a specific direction |
| Value | Always non-negative (≥ 0) | Can be positive, negative, or zero |
| Example | A car travels at 60 km/h. | A car travels at 60 km/h due north. |
An object can have a constant speed while its velocity is changing. For example, a car driving in a circle at a constant 50 km/h has a constant speed, but its velocity is constantly changing because its direction is always changing.
The total displacement of an object divided by the total time interval. It describes the overall motion over a period but does not give details about the motion at any specific moment.
The velocity of an object at a single, specific instant in time. It is what a speedometer in a car reads, along with the direction of travel at that moment. Mathematically, it is the limit of the average velocity as the time interval approaches zero. The magnitude of the instantaneous velocity is the instantaneous speed. On a displacement-time graph, the slope of the tangent at any point gives the instantaneous velocity.
An object moves with uniform (or constant) velocity if it covers equal displacements in equal intervals of time. This implies that both its speed and direction of motion are constant. An object with uniform velocity has zero acceleration.
Q: Can an object's average velocity be zero even if its average speed is not? A: Yes. This happens when the object's total displacement is zero, meaning it ends its journey at the same point it started. For example, completing one lap on a racetrack.
Q: What does a negative velocity signify? A: A negative sign on velocity indicates its direction relative to a chosen coordinate system. For example, in one-dimensional motion, a positive velocity might mean moving to the right, while a negative velocity would mean moving to the left.