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## High school physics

### Course: High school physics>Unit 1

Lesson 3: Average velocity and average speed

# Average velocity and speed review

How to calculate average velocity and speed in one-dimension in word problems

## Equations

EquationSymbol breakdownMeaning in words
v, with, \bar, on top, equals, start fraction, delta, x, divided by, delta, t, end fractionv, with, \bar, on top is average velocity, delta, x is displacement, and delta, t is change in time.Average velocity is displacement divided by time interval of the displacement.
v, start subscript, start text, a, v, g, end text, end subscript, equals, start fraction, d, divided by, delta, t, end fractionv, start subscript, start text, a, v, g, end text, end subscript is average speed, d is distance, and delta, t is change in time.Average speed is distance divided by time interval for the distance traveled.

## Common mistakes and misconceptions

• Average speed does not have to equal the magnitude of the average velocity. People may think that average speed and average velocity are just different names for the same quantity, but average speed depends on distance and average velocity depends on displacement. If an object changes direction in its journey, then the average speed will be greater than the magnitude of the average velocity.
• Speed is a scalar, and average velocity is a vector. Average velocity indicates direction and can be represented as a negative number when the displacement is in the negative direction. Average speed does not indicate direction and can only be positive or zero.

To check your understanding and work toward mastering these concepts, check out our exercises on:

## Want to join the conversation?

• What would the displacement be when going around a circle?
• Imagine or get two thumbtacks. Stick thumbtack 1 in while making thumbtack 2 go in a circle starting from thumbtack 1. Stop thumbtack 2 wherever you want in the circle you're creating, and stick it in. Then tie a string from thumbtack 1 to thumbtack 2. THAT STRING IS YOUR DISPLACEMENT AND THE PATH YOU TRAVELED IS YOUR DISTANCE:
• I've worked in the aerospace industry for 40 years. In all that time I've never once come across negative velocity. If I told my colleagues about this concept, they've wouldn't believe it.
• My guy, if you are 40 years old and are an engineer, why are you on a khan academy page for high school physics 💀
• When it asks for a significant number, what would 0.0008 be?
• I'm confused, because in this article, it says average speed is written as Vavg (V with a lowercase "avg"), but in Sal's video, he writes average velocity as the same thing. Which should I follow?
• vavg​, start subscript, start text, a, v, g, end text, end subscript is average speed
(1 vote)
• My question is...when someone reached to his car and then go back to his home because he forgot something, the average speed cannot be 0 because he has walked at least few meters. So, how am I suppose to calculate the average velocity?
• Well the average velocity is displacement divided by time, so If Jonny walks to his truck from his house and realizes he forgot his wallet and then goes back to the house where he started over 68 seconds, his average velocity would be zero. The reason for that is because his displacement would be none, displacement is how far the object is from its original position, not the total distance traveled. Hope this helps!
• if they ask us to round of to 2 significant values do we round of the greater or lower digit for ex 3.344 should be rounded off to 3.35 or 3.34
(1 vote)
• Rounding 3.344 to two significant digits would be 3.3. (in your example, rounding to 3.34 would be rounding to two decimal places)