Average Speed vs. Average velocity

caprija

Do you think that average speed and average velocities are usually the same for something in motion?

radou

Generally, they are synonyms, but velocity is usually used in the context of physics, I guess.

caprija

Ya I mean in Physics.

Are they the same? what are the differences?

radou

I guess there's no difference, except that you usually don't use the term 'speed' in physics.

caprija

Thanks

I have one more question, to find the instantaneous speed between lets say 0 and 3 seconds using a distance vs. time graph. I first draw the line fo best fit then I would find the slope right?

MeJennifer

It is like comparing apples and pears, they are completely different. One is a scalar the other is a vector quantity.

neutrino

Actually, the average speed is the [tex]\frac{total distance travelled}{total time taken}[/tex], while average velocity is [tex]\frac{total displacement}{total time taken}[/tex]. Remember, the displacement can be zero when the distance is not.

caprija

ok so i'm confused now, when we're talking about something in MOTION is the average speed and the average velocity usually the same?

radou

Hm, could you clarify what you meant by that?

Omega_6

It is possible to have an average velocity of zero, for example.

(You travel at 5 m/s for 2 sec and then you travel at -5 m/s (backwards) for 2 sec)

...and not so with speed (it is a scalar quantity).

radou

I know, but I still don't understand the statement above. Nevermind.

caprija

I wrote:

"I do think that average speed and average velocity are usually the same for something in motion because it's still measuring time. The only diffference is that when calculating the velocity, you're calculating the rate at which the object changes it's postition."

does that sound about right?

neutrino

Went offline for some time...What exactly did you not understand?

Checkfate

Speed is a scalar quantity. If we designate forwards as positive movement and backwards as negative movement. I can run back and forth at 1m/s and arive where I started and my speed would still be 1m/s.

Now if we are using velocity, it is a VECTOR quantity. This means that you need to indicate MAGNITUDE and DIRECTION.

If you were to run 30,000 miles forward and then 30,000 miles backwards in 3 hours, your speed would be [tex]v=\frac{60000miles}{3hours}=\frac{20000miles}{hour} [/tex]

BUT if you were to give velocity... [tex]\vec{v}=\frac{(30000miles)+(-30000miles)}{3hours}=\frac{0miles}{3hours}=\frac{0miles}{hr} [/tex]

Get it?

Notice the arrow above v to designate whether it is a scalar quantity of a vector quantity.. [tex] \vec{v}=velocity [/tex] [tex] v=speed [/tex]

radou

If you are so 'aware' of the difference between vector and scalar quantities, then you should be more careful when writing equalities.

caprija

Yes, Thanks I get it.

But the question is really confusing, are they usually same or not?

neutrino

If you're moving with a constant velocity (speed is constant, direction is constant), then the magnitude of average velocity = average speed. In such a case, the dist-time graph will always be a straight line.