What is the difference between Average Speed and Average Velocity?

Question

From what i understood in class, average speed and average velocity are the same, but average velocity must be + or -. Is that true? Also, Average velocity, isn't it the same as velocity, displacement/time?

If what i'm saying is right, then
Vaverage = (0m-30m)/(15.8sec-9.23sec) = -4.57 m/s, but Speed (avg) = 4.57 m/s

Is that right?

Answer 1

Average velocity is total displacement/time and includes direction.
Average speed is just the distance you covered/time it took.

Lets say I was on a football field and ran from the 50 yard line, to the goal line, and then back to the 40 yard line, all in a time of 10 seconds. My average speed will be the total distance I ran (90 yd) divided by the time it took (10s). So avg speed is 9m/s.

My average velocity will be the total displacement (10yd) divided by the total time (10s), and will therefore be +1m/s.

Also, lets say we started at the 50 again and ran 20yds backwards in a time of 5 seconds. My avg speed will be 4m/s. But my avg velocity will be -4m/s because we had already established forwards as the positive direction.

Answer 2

Given that I don't know the statement of the problem... I'm willing to say your answers sound correct, but you're oversimplifying the difference between speed and velocity.

If I said, "I traveled one mile north, then 1 mile south, ending at the same spot, total trip took me 2 hours", then my average speed is 1 mph, since it took me 2 hours to travel 2 miles. However, my average VELOCITY is 0 mph, since for half the trip my velocity was the opposite of what it was for the other half of the trip.

Speed measures how fast you're traveling. Velocity includes what DIRECTION you're traveling.


Here's some links

Answer 3

Velocity is a vector. It has a direction and a magnitude (how much) associated with it.

Do you know what the magnitude of a vector is? It's expressed like this:

Say you have a velocity vector "v":

v = v1i + v2j + v3k

The magnitude of "v" is: |v| = √[(v1i)² + (v2j)² + (v3k)²]

Well...speed (s) is equal to this magnitude: s = |v|

Average speed is the average 'magnitude' of velocity in time of the vector 'v'. Average velocity sort of is an average of the speed, but also direction as well.

Make any sense?

Answer 4

Speed is a scalar quantity such as the length of a vector. Velocity is a vector quantity which implies direction and amplitude.

So when you work out an average speed you usually do for example (V2 - V1)/2 = Vaverage which is a number.

For average velocity you must have (vector V1 - vector V2)/2 = vectorVaverage which is another vector which makes up a triangle whose sides are V1, V2 and V2 -V1 all taken as vectors .

Answer 5

Speed is always a positive number.

Velocity is speed & direction. So a speed in a positive direction can cancel a speed in a negative direction.

Answer 6

I think velocity also refers to direction...