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Speed and velocity
5

Speed and velocity

Speed and velocity

(OP)

In Physics and Mechanics, although both refer to rapidity, and rate of change of position, is there a real difference between these two words ? For example, speed -without regard to direction- could be interpreted as the magnitude of the velocity vector which has direction and magnitude. Any comments ?

RE: Speed and velocity

There you go.

RE: Speed and velocity

I suppose that speed can also be a kind of beahaviour. velovity is nothing but a vector.

RE: Speed and velocity

yep, pretty much as it is ...
speed is the scalar of velocity (which is a vector)

RE: Speed and velocity

I'm not sure if I see this distinction between the two. For example wind speed is not just a scalar but is a vector by definition, isn't it? A value for speed without a direction would be meaningful only in a onedimensional world (assuming the direction is indicated by the number being positive or negative). In a >1 dimensional world you'd always need to express speed as a vector for it to give you any meaningful information.

RE: Speed and velocity

When a value for speed is given without a direction isn't it generally assumed that the direction is the direction of motion at the instant in time pertaining to the value? For example, the speed of a conveyor would be the speed in the direction that the conveyor is constrained to move.

A vehicle speed is assumed to be the speed in the direction of travel. That may work to your advantage if a traffic officer measures your speed by radar. The measured speed is the speed along a line between the vehicle and the radar unit at the instant of measurement. If that direction is not identical with the direction of travel, the measured speed will be less than the actual speed in the direction of travel.

RE: Speed and velocity

The scalar/vector distinction is the one I was taught as a youngster, and still makes sense to me.

Don't think I agree completely with Epoisses - If you're bothered about your chimneys, the wind direction is irrelevant (provided you've taken shelter far enough away).  The damage is an outcome of the scalar quantity - the chimney won't heal itself if the wind changes direction.

A.

RE: Speed and velocity

I agree that speed is magnitude only, whereas velocity includes direction.  However, I see these misused all the time. For example, the line "What is the airspeed velocity of an unladen swallow?"  However, as the Pythons are not engineers, I'm likely to forgive them.

RE: Speed and velocity

Holidays or Vacations?


Should one say I go for holidays with a great speed?


or I go for vacations at high velocity?

or can I say: I go for holidays with a great speed at high velocity?


sunshine  

RE: Speed and velocity

Looking in two dictionaries, velocity is the same thing as speed.  Given this, perhaps we can forgive laymen who are not familiar with our physics or engineering jargon.  Dictionary.com goes as far as to differentiate between a typical definition of velocity and the use of the term for physics.

RE: Speed and velocity

0707,

   You can go for vacations with great speed at high velocity, but the police are going to be interested.

                  JHG

:)

RE: Speed and velocity

I have never stayed up all night on velocity.

RE: Speed and velocity

I feel use of these words is contextual.

In a scientific description it might be more appropriate to use the terms according to their scientific meanings. However, in general conversation using velocity could be for emphasis assuming the audience recognise it as mere speed!

RE: Speed and velocity

"velocity" is often used in a journalistic context because it gives a greater emphasis than the word "speed", understood by Joe Public. "High velocity" has more oomph than "High speed" when used to describe a car/plane/boat to the masses.

RE: Speed and velocity

Khumbu and SomtingGuy,

Good points. There is often a very big difference in meaning of a word between the general public and the scientific community.

"*" to you both.

"Do not worry about your problems with mathematics, I assure you mine are far greater."   
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

RE: Speed and velocity

WHAT CRAP.  The original post asked and answered the question.  Everything since has been nonsense.  If Dictionary.com or Dan Rather think that ignoring the established technical definitions is proper behaviour then we should ignore them.  "Speed" is the magnitude of "Velocity".  Velocity must always have a direction.  Speed can never have a direction.  Some pompus ass thinking he sounds "more important" by saying "high velocity" instead of "high speed" does not in any way change the basic definitions.

We're engineers.  This should be easy.  If we accept sloppy use of the language then we deserve a progressive deterioration in its precision.

David

RE: Speed and velocity

....and in the last seat of the bus, while staring out a window, a lone stranger quietly chants: "zdas04! zdas04! zdas04!"

RE: Speed and velocity

Definitions of words change all the time throughout history.  Resist it long enough and you'll find yourself speaking a dead language to yourself.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

RE: Speed and velocity

If you are billing by the hour use 'velocity.'  If you are giving free advice, say speed.

rmw

RE: Speed and velocity

Quote:

I agree that speed is magnitude only, whereas velocity includes direction.  However, I see these misused all the time. For example, the line "What is the airspeed velocity of an unladen swallow?"

Were those African or European swallows?

Speaking of velocity.  In rotating machinery vibration we look at displacement, velocity, and acceleration.  It doesn't matter whether we're considering the direction or not, it's always called velocity, never speed.

I'm not saying that's right. But speed would sound pretty darned funny.  I'm going to try it on my boss next week. The bearing housing speed increased to 0.3 inches per second.  LOL!

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Speed and velocity

I hope you always give your shaft speeds as velocities:

"Can you take it up to an angular velocity of -200 pi radians per seconds about the longitudinal axis of the crankshaft, please?"

sounds much posher than

"floor it and bounce it off the rev limiter, mate"

Cheers

Greg Locock

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