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Difference Between Average Speed and Average Velocity

speed-pdAverage Speed vs Average Velocity

Physics definitely has a way of making things difficult, at least for the common mind. However, one should consider that scientists, engineers, and physicists need to differentiate terms for a more accurate experimentation and data analysis. Thus, we go into the world of speed and velocity. Yes, most of us know that the first one is scalar and the latter is a vector quantity. However, I’m pretty sure that when you are asked about the difference between average speed and average velocity, you can’t actually elaborate more than the scalar and the vector aspects.

If you think that both measurements will usually give the similar values, then, you’re wrong. When it comes to traveling, average speed and average velocity will often differ, and perhaps by large quantities.

We are all taught that when a car is moving forward, and has reached its destination at a straight distance of 10 km, in a time of 1 hour, then the speed will be 10 km/h, and the velocity will be 10 km/h north, assuming, that you are indeed going northwards. Well, that was quite easy; just add a direction and voila! Instant conversion. If only it were that easy!

In average speeds and average velocities, the direction may change and the speeds may vary, therefore, the calculations may somehow become a bit more complex. Then again, don’t get intimidated, as it is quite easy when you get the grasp of it.

Once again, when you refer to speed, it is not a vector expression, therefore no direction is involved. Average speed is all about the total distance traveled divided by the total time taken. A car from point A reaching an exact point B will have an average speed by adding all the distance covered divided by how long it took to get there. Note that the traveling directions can go east, then west, zigzag, or back and forth; the destination point can even go back to the starting point. Average speed doesn’t care about the displacement from the origin, only the total distance covered to get to the destination.

Consider this equation when trying to calculate the average speed of traveling from points A to D:

Average Speed = (Distance from A to B + Distance from B to C + Distance from C to D) / Total time taken to get from A to D

Assuming that the total distance traveled is 100 km, and it took 1 hour to get there, the average speed is 100 km/h

Average Velocity is totally different, not to mention that it is a vector quantity (with direction). Average speed can reach an enormous value, while the average velocity may be very minimal, even zero. This is possible due to the different way of calculating the average velocity. The main difference is the factor used in the calculation, and that is the ‘Displacement’. The displacement does not care about the distance of the whole course, as it only deals with the direct distance from the origin to the destination.

The formula is very similar to that of average speed, but instead of the total distance covered, it is supplanted by displacement. Here is the formula of the average velocity of traveling from A to D:

Average Velocity = Displacement from A to D / Total time taken to get from A to D

The direct distance (displacement) from A to D could well be very small. Thus, the average velocity can be very minimal. A zero displacement can even occur when the destination came back to the origin. In this case, the average velocity is also zero.

So, if the displacement from point A to point D is only 5 km east, and it took an hour to get there, regardless of the 100 km travel distance, the average velocity is only 5 km/h east.

If the direction of the whole course is straight, the average speed and the average velocity will be equal.

Summary:

1. Average speed is a scalar quantity, while average velocity is a vector quantity.

2. Average speed takes into account the total distance traveled, while average velocity is concerned with the displacement between two points.

3. In average velocity, direction is expressed.

4. More often than not, the values will differ, with average speed usually having the higher value.

5. Average velocity can be equal to zero, even when the body has completed a traveling motion, as long as the destination point is back at the origin. In this case, the average speed will always have a greater value.


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5 Comments

  1. Great explanation! It is totally worth to be put in a physics textbook!

  2. I learnd many things..well done!!

  3. Awesome explanation, great work!! Keep it up!

  4. THANKS so much. It helped me understand my physics homework.

  5. very helpful, did my homework, love u man +1 ,

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