Speed and Velocity

When dealing with moving objects we come across the terms speed and velocity and in our everyday verbiage, we often used the word speed and velocity interchangeably.

We act as if they have the same definition, but they actually have different definitions, so it’s important to differentiate between the two. I’m going to start off with giving you the definition of speed.


The transcript is provided for your convenience
Speed is a scalar quantity and so when I say it’s a scalar quantity that means that it has magnitude, but no direction. Then we have velocity, which we call a vector quantity and so when we say some thing’s a vector quantity that means it has magnitude and direction. You can see the difference here, as was speed and velocity, we’re both interested in how fast an object is moving. But with speed it doesn’t matter if that object changes direction. Whereas velocity, the specific direction an object is moving is very important and when that changes, the velocity changes.

Say we have a car right here, pretend it’s an 18 wheeler and so it’s moving at a speed of 70 kilometers per hour and so it’s moving, it’s moving, it’s moving and then it comes around this corner or this curve and so it’s speed is still 70 kilometers per hour. Its speed had no change, because this 18 wheeler is still moving at the same rate, still moving as fast as it was before. But, see the velocity did change, because velocity is too full, not only is it concerned about a magnitude, but it’s also concerned about direction.

If either one of those changes, then the velocity changes and so since the direction changed, the velocity changed, because we could further define velocity as specified speed in a specified direction. The specified speed didn’t change, but the specified direction of the 18 wheeler moving this way did change and so now the curve has made the 18 wheeler move in a different direction. The velocity we can say has changed and so when you go around a corner in a car, even though you’re maintaining the same speed you change velocity. Any change in velocity such as change in speed, direction or both constitutes an acceleration and requires the net unbalanced force act upon the moving system, so that’s the difference between speed and velocity.