difference between speed and velocity in physics

Speed

The best way to start examining the difference between speed and velocity is to look at your car's speedometer. The next time you're in your car on the highway, do just that. What does it say? I'm going to assume you always obey the speed limit, so if the speed limit is 65 miles per hour, your speedometer should read 65 miles per hour. This means that if you drive for 65 miles, it will take you an hour.
It doesn't matter where you're driving to, how many turns the road takes, or if you're on a big, circular track. Speed is only concerned with how much ground you've covered in the time you've been driving. To put an official definition on it, speed is how much distance is covered over a specific period of time, regardless of direction traveled. Since there is no directional component, speed must be a scalar quantity.
In physics, you can calculate average speed by taking the total distance traveled and dividing it by the total time required to travel that distance.
Average speed = total distance / time
So, if we know Jimmie Johnson drove 500 miles, and I tell you it took 3.14 hours, we can calculate his average speed.
Average speed = 500 miles / 3.14 hours = 159 miles/hour
Remember, for the speed, it doesn't matter that he was driving in a big circle. But that circle will matter soon.

Velocity

Speed is a scalar quantity, so you can probably guess that speed has a corresponding vector quantity that combines how fast an object is traveling and its direction of travel. This vector quantity is velocity, defined as the rate at which an object changes position.
Remember that in physics a change in position from its starting point to its end point is an object's displacement. The exact route doesn't matter here - only the direct distance from start to finish. Displacement always has both a magnitude and a direction.
Let's look at the equation for average velocity:
Average velocity = displacement / time
In this equation, velocity is represented by a letter v with a bar over it. This line indicates we want an average. The change in displacement is delta s, and the change in time is delta t.
To illustrate velocity, let's go back to Daytona. We calculated Jimmie Johnson's average speed, but what about his average velocity? Daytona speedway is shaped as seen below. The point on the track where the car is serves as both the starting line and the finish line.
If we trace Jimmie's path along the track for one lap, he starts and ends at the same position, making his total displacement 0. Even though he drives many laps and covers 500 miles, he always starts and ends at the same point, making his total displacement for the entire race 0. To calculate his average velocity:
Average velocity = 0 miles / 3.14 hours = 0 miles/hour
As you can see, his speed was 159 miles per hour, but his velocity was 0 miles per hour.