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Old April 23 2010, 03:23 AM   #1
ReadyAndWilling
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Speed versus velocity?

hey guys, can anyone explain to me the difference between speed and velocity?

thanks
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Old April 23 2010, 06:05 AM   #2
sojourner
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Re: Speed versus velocity?

http://dictionary.reference.com/browse/speed

http://dictionary.reference.com/browse/velocity

Um, none?
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Old April 23 2010, 06:13 AM   #3
PurpleBuddha
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Re: Speed versus velocity?

ReadyAndWilling wrote: View Post
hey guys, can anyone explain to me the difference between speed and velocity?

thanks
Do you mean acceleration vs velocity?
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Old April 23 2010, 06:19 AM   #4
sojourner
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Re: Speed versus velocity?

^ Yea, that's easy. Acceleration is how long it takes something to get up to speed.

Example:

You know a car can do 60mph. 60mph is the speed.

How long does it take the car to go from 0mph to 60mph? That would be it's rate of acceleration.
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Old April 23 2010, 06:30 AM   #5
PurpleBuddha
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Re: Speed versus velocity?

^ That.

Or put even more simply, acceleration is the rate of change in velocity.
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Old April 23 2010, 02:20 PM   #6
Pavonis
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Re: Speed versus velocity?

Speed is a scalar.

Velocity is a vector.

That's a distinct and fundamental difference between the two terms.

It's the difference between "Drive 50 mph to get to my house" and "Drive 50 mph north to get to my house".
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Old April 23 2010, 02:34 PM   #7
Jadzia
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Re: Speed versus velocity?

It's similar to the distinction between distance and position.
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Old April 23 2010, 03:44 PM   #8
Lindley
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Re: Speed versus velocity?

Pavonis wrote: View Post
Speed is a scalar.

Velocity is a vector.

That's a distinct and fundamental difference between the two terms.

It's the difference between "Drive 50 mph to get to my house" and "Drive 50 mph north to get to my house".
That's it exactly.

A velocity in 3D space might look like <5, 6, 7> in the x,y,z directions. But the assocated speed would be sqrt(5*5+6*6+7*7) = 10.5.

Speed and velocity reduce to the same thing in a 1-dimensional space.
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Old April 23 2010, 04:03 PM   #9
Asbo Zaprudder
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Re: Speed versus velocity?

Lindley wrote: View Post
Speed and velocity reduce to the same thing in a 1-dimensional space.
[nitpick] Not quite, an object could have a speed of 5 m/s in either the +ve or -ve direction, which would be equivalent to velocities of +5 m/s or -5 m/s respectively. [/nitpick]
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Old April 23 2010, 04:07 PM   #10
Lindley
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Re: Speed versus velocity?

Okay, granted.
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Old April 24 2010, 04:38 PM   #11
ReadyAndWilling
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Re: Speed versus velocity?

Pavonis wrote: View Post
Speed is a scalar.

Velocity is a vector.

That's a distinct and fundamental difference between the two terms.

It's the difference between "Drive 50 mph to get to my house" and "Drive 50 mph north to get to my house".
hey man, thanks for the reply. can you explain that example a bit more?
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Old April 24 2010, 04:57 PM   #12
The Badger
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Re: Speed versus velocity?

Speed is how fast something travels.

Velocity is how fast something travels in a particular direction.
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Old April 24 2010, 06:17 PM   #13
sojourner
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Re: Speed versus velocity?

^Sounds the same to me. Unless you view velocity as a subset of speed?
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Old April 24 2010, 06:18 PM   #14
FordSVT
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Re: Speed versus velocity?

I'll say it again in another way just for fun!

Speed = rate of movement over time. 50 meters per second, a scalar quantity.
Velocity = rate of movement over time + a direction. 50 meters per second @ 45 degrees, a vector quantity.


Ooooo! Ooooo! Rule of thumb! Rule of thumb! Lets add some!
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Old April 24 2010, 06:36 PM   #15
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Re: Speed versus velocity?

Velocity specifies direction, speed does not.
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