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Average Velocity

Teacher/Instructor Matt Jones
Matt Jones

M.Ed., George Washington University
Dept. chair at a high school

Matt is currently the department chair at a high school in San Francisco. In his spare time, Matt enjoys spending time outdoors with his wife and two kids.

The average velocity of an object over a given period of time is found by dividing the distance it has traveled by the time elapsed. Because velocity refers to the rate at which an object changes position, it is a vector quantity and direction matters. This differentiates average velocity from average speed. The formula for average velocity is (the change in x) / (the change in t) or (x2-x1) / (t2-t1).

Let's talk about Average Velocity. So what's the difference between speed and velocity? Well speed is distance over time 100 kilometers an hour, velocity is very similar 100 kilometers per hour but it's in a specific direction, so 100 kilometers per hour east would be a given velocity okay? Well how do we solve a velocity problem? And how is it different than solving a speed problem?

Let's look in an example. Let's say I travel a hundred kilometers north in 2 hours then travel 60 kilometers east in 30 minutes, if this was a speed problem, I could just add those up and divide okay? But this is a velocity problem so I've got to solve that as two separate velocities cause they're not the same okay? So I say 150 kilometers in 2hours that's going to equal 75 kilometers an hour north okay? Then I have 60 kilometers east in 30 minutes, and if you look here I've got hours from my one velocity and minutes from my second. I don't want to have two separate units for that I'm want to simplify that and just let's just keep it hours okay? So instead of saying 60 kilometers in 30 minutes, let's convert 30minutes into hours okay? So I'll say we got 60 kilometers in 0.5 hours that's going to equal 120 kilometers an hour and in this case that's east which is a separate velocity than our initial velocity so answer here we have 100, 75 kilometers an hour north and then 120 kilometers east and that's how we calculate average velocities.