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### Course: Mechanics (Essentials) - Class 11th > Unit 4

Lesson 3: Why do we need both distance and direction to truly grasp motion?- Intro to vectors and scalars
- Average speed & velocity (with examples)
- Average velocity and speed in one direction: word problems
- Average velocity and speed with direction changes: word problems
- Average speed for entire journey - solved numerical
- Average velocity and speed review

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# Average velocity and speed review

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

## Equations

Equation | Symbol breakdown | Meaning in words |
---|---|---|

Average velocity is displacement divided by time interval of the displacement. | ||

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.

## Learn more

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?(35 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:

Visit link for example:

https://www.google.com/url?sa=i&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwiN0-HA3drgAhU6JTQIHdnXDhEQjRx6BAgBEAU&url=https%3A%2F%2Fwww.quora.com%2FA-body-is-moving-along-a-circular-path-of-radius-r-What-will-be-the-distance-and-displacement-of-the-body-when-it-completes-half-a-revolution&psig=AOvVaw2ahScm9ik2ti3H8hx2vSLS&ust=1551316231398291(58 votes)

- 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.(27 votes)
- The "negative" Velocity just indicates that you are moving south or west. In most engineering firms for clarity, they don't just write a negative sign as it can be confused for south or west, and can be both. Instead they write x meters South or West, or whatever direction they need, as it is much more clearer and only one direction is possible, unlike the two with the negative sign which could confuse people working, and the negative sign would make no sense to those working who have never taken physics before or don't remember it.(2 votes)

- 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!(20 votes)

- When it asks for a significant number, what would 0.0008 be?(10 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?(7 votes)
- vavg, start subscript, start text, a, v, g, end text, end subscript is average speed(2 votes)

- what does "your answer should be an exact decimal." because on my calculator for example the answer would be 0.37 and when i went to put it in the answer would be 0.38 and i was getting lots of questions wrong because of this. am i doing something wrong or is it me being dumb?(4 votes)
- The question says to round off your answers to two significant figures.

Did you get 0.37 exactly? I don't think so. If you got other digits after 0.37, then the reason why the correct answer is 0.38 is because the digit after 7 in 0.37 is a digit that can be rounded up so 1 will be added to 7 to make the answer 0.38 instead of 0.37

In mathematics, when writing numbers in two significant figures, you must not forget to round up or down.

You should probably brush up on rounding numbers up or down for better understanding.

Hope this helps:)(3 votes)

- How is average velocity a vector? Is it because it is direction-aware?(3 votes)
- 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.(2 votes)

- I get the math I mess up the displacement and the velocity sometimes.(4 votes)
- Displacement is the theoretical amount traveled. Velocity is the rate in which the object changes its position. First find the displacement, then divide it by the time to get your velocity.(2 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(2 votes)
- 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?(3 votes)
- By the way I found the answer was 3.3m/s, where you don't divide 150 seconds by 2.

http://msgrantsphysics.weebly.com/uploads/2/1/3/3/21339258/ap_physics-1d_linear_motion_exam_review.pdf(3 votes)