Speed versus velocity?

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

thanks

 

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

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

Um, none?

 

Do you mean acceleration vs 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.

 

^ That.

Or put even more simply, acceleration is the rate of change in 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".

 

It's similar to the distinction between distance and position.

 

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.

 

[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]

 

Okay, granted.

 

hey man, thanks for the reply. can you explain that example a bit more?

 

Speed is how fast something travels.

Velocity is how fast something travels in a particular direction.

 

^Sounds the same to me. Unless you view velocity as a subset of speed?

 

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!

 

Velocity specifies direction, speed does not.

 

Speed is the magnitude of velocity.

 

Does that direction have to be in specific terms? Or can you just say, "I'm going to drive over there at 50 mph."? Would that count as velocity?

 

That's starting to get into the vagaries of English. I'd say no, not in scientific terms.

 

What's great about the difference between speed and velocity is when we start talking about acceleration.

Acceleration is the time rate of change of VELOCITY. That's why something moving at a constant speed, yet turning, is still said to be accelerating.

 

Hey, now you're just pulling my G forces.