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

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

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radou

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

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Ya I mean in Physics.radou said:Generally, they are synonyms, but velocity is usually used in the context of physics, I guess.

Are they the same? what are the differences?

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radou

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

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

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?

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It is like comparing apples and pears, they are completely different. One is a scalar the other is a vector quantity.caprija said:Do you think that average speed and average velocities are usually the same for something in motion?

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

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radou

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neutrino said:

Hm, could you clarify what you meant by that?

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radou said:Hm, could you clarify what you meant by that?

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).

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radou

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Omega_6 said: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)

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

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"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?

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Went offline for some time...What exactly did you not understand?radou said:I know, but I still don't understand the statement above. Nevermind.

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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]

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]

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radou

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Checkfate said:...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]

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

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Yes, Thanks I get it.Checkfate said: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]

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

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In every day conversation, if someone were to ask you what velocity your ride can get you to school and back, and you're school is 200m away from your home, they are confusing speed with velocity. Lets say your car can get to school and back home in 10 minutes, well the velocity is [tex] \vec{v}=\frac{200m+(-200m)}{10min}=0m/min [/tex] This would be correct, but obviously they are asking for speed.

While in school, I would say that__velocity and speed are NEVER the same past grade 10__. If a question asks for the velocity, you must take vectors into account as giving the speed will be wrong! Speed is NOT velocity, even though many people whom forget about physics class assume it is :P Get it?

While in school, I would say that

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lol ya thanks for trying.Checkfate said:

I'm in grade 10, so this is all new to me. We're learning how to calculate average speed/velocity and instantaneous speed/velocity using secent and tangent methods.

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I forget how to calculate the instantaneous velocity and speed using a graph.

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By "tangent methods" do you mean differentiation? Have you ever heard the term derivative? I am in grade 12 and am just learning about it now :P

But to calculate the ALMOST instantaneous speed using a graph, simply draw a secant from one point to a point fairly close and estimate the slope. I think thats about as close as you can get without using calculus.

Just remember these definitions, they are right out of my physics book.

If you take physics 20 next year, you will learn plenty about vectors and scalars, :).

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Thanks for the definitions, I wrote them down lolCheckfate said:

By "tangent methods" do you mean differentiation? Have you ever heard the term derivative? I am in grade 12 and am just learning about it now :P

But to calculate the ALMOST instantaneous speed using a graph, simply draw a secant from one point to a point fairly close and estimate the slope. I think thats about as close as you can get without using calculus.

Just remember these definitions, they are right out of my physics book.

: A quantity, such as velocity, completely specified by a magnitude and a direction.vector

: A quantity, such as mass, length, or speed, that is completely specified by its magnitude and has no direction.scalar

If you take physics 20 next year, you will learn plenty about vectors and scalars, :).

i got the instantaneous speed, how would calculate the instantaneous velocity? Which points do you use?

The question asks "What is the instantaneous velocity between 0 and 3 seconds?"

To get the speed I i used rise/run (line of best fit) got 2/3 = 0.7 km/min

which points do i use to find the instantaneous velocity?

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radou

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Checkfate said:...

: A quantity, such as velocity, completely specified by a magnitude and a direction.vector

...

Whoa, slow down just a little bit. A vector is completely specified by:

http://csep10.phys.utk.edu/astr161/lect/history/velocity.html"

Case closed.

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I have not yet seen a vector where the orientation was declared. But anyways.

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