AP®︎/College Physics 1
Average velocity and speed review
How to calculate average velocity and speed in one-dimension in word problems
|Equation||Symbol breakdown||Meaning in words|
|is average velocity, is displacement, and is change in time.||Average velocity is displacement divided by time interval of the displacement.|
|is average speed, is distance, and 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?(31 votes)
- 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:
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- 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.(21 votes)
- My guy, if you are 40 years old and are an engineer, why are you on a khan academy page for high school physics 💀(5 votes)
- When it asks for a significant number, what would 0.0008 be?(9 votes)
- 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?(6 votes)
- 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?(2 votes)
- 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!(3 votes)
- 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)(6 votes)
- How would you calculate the displacement if for example, an object moved north (vertical) and then east (horizontal)? Im struggling to find the Avg. Velocity for this question: "A truck traveled 400 meters north in 80 seconds, and then it traveled 300 meters east in 70 seconds. The magnitude of the average velocity of the truck was most nearly (answer)." My professor said the answer was 6.6 m/s. But how?(2 votes)
- By the way I found the answer was 3.3m/s, where you don't divide 150 seconds by 2.
- What would the displacement be if it was curved downwards.(2 votes)
- Well just like a graph, you could count left and down as negative and right and up as positive. So the displacement downward would be negative.(1 vote)
- According to Fundamentals of Physics by Halliday, Resnick, and Walker, average velocity is written as v_avg, while average speed is written as s_avg . This is what I studied with during my graduate school years in Physics.(2 votes)
- How is average velocity a vector? Is it because it is direction-aware?(1 vote)
- since average velocity depends on displacement which is a vector ( both magnitude and direction are considered) average velocity os a vector, and yes 'cause it's direction-aware.(1 vote)