# But I'm sure! Speed and velocity are the same thing!

1. Dec 24, 2012

### Weissritter

Yeah, I know the differences between speed and velocity. In common life, however, I may use them as if they were the same. Guess my science-brain isn't that much active sometimes.
While this thread is physicist-targeted, anyone's reaction is welcome.
You know the difference between those two words, right? How do you feel when common people use them as if they meant the same? Have you ever objected at their actions, or you just sigh again, as if no effort could stop the misuse?

2. Dec 24, 2012

### Staff: Mentor

Velocity as a vector quantity versus speed as a scalar quantity (magnitude of the velocity) is purely a convention among physicists. I learned just today that it appears to have been started by J. W. Gibbs around 1901. He wrote the first textbook (as opposed to lecture notes) that taught the vector mathematics that we use today.

When I'm dealing with non-physicists in a non-physics context, I don't expect them to know the difference, nor do I make a point of it.

Last edited: Dec 24, 2012
3. Dec 24, 2012

### Pythagorean

I don't expect laymen to recognize the distinction.

4. Dec 25, 2012

The one thing that does get me is when lay persons try and tell me deceleration is not acceleration.

5. Dec 25, 2012

### lisab

Staff Emeritus
Same here, and I try not to let them see my eye twitch.

6. Dec 25, 2012

### Sdtootle

I very rarely hear anyone say velocity. I almost always hear then say speed, but I rarely have issue if they misuse it outside of a technical environment.

I get more upset when people mix up your and you're on Facebook.

7. Dec 25, 2012

### zoobyshoe

Some people just don't realize "your" is scalar and "you're" is a vector.

8. Dec 25, 2012

### Weissritter

For now we have no murder desire, so it is kinda good. When it comes to your and you're things do become more annoying.
Do we have more opinions?

9. Dec 25, 2012

### Jorriss

In nonacademic talk, I pretty much use speed exclusively.

10. Dec 25, 2012

### Staff: Mentor

And that "your'e" is imaginary.

11. Dec 25, 2012

### fluidistic

I don't feel bad when someone misuses velocity for speed, my brain just pops up a "wrong" message. The same happens when I hear/read "weight ... kg".

12. Dec 25, 2012

### Pengwuino

Greatest line ever.

13. Dec 25, 2012

### Pythagorean

or "mass.. lbs"

14. Dec 25, 2012

### aquitaine

Or using "lightyear" as a measure of time.

15. Dec 26, 2012

### Weissritter

This gives me a controllable murder desire :grumpy:

Also forgot the highest one: saying "degrees kelvin" :grumpy::grumpy: The worst part is that most people who say this are not common non-physicist. They are usually scientists, who are supposed to know this. It becomes worse when something as big and inspected as "The Avengers" makes that mistake.

16. Dec 26, 2012

### Staff: Mentor

So wait. Should we be using the term "escape speed" instead of "escape velocity" now?

17. Dec 26, 2012

### Jimmy Snyder

But in this case direction matters.

18. Dec 26, 2012

### D H

Staff Emeritus
This confusion is our fault rather than a confusion in the lay community. The technical world is the one that had a problem with the term "weight", not the lay community. This technical confusion wasn't resolved until 1901 when, by dint of a bureaucratic decision, weight was deemed to denote "a quantity of the same nature as a 'force'."

The lay community was and is just fine with weight being a non-technical synonym for the technical concept of mass. Legally, the term "weight" is still a synonym for mass in the US. A one pound can of beans weighs one pound at the South Pole, at the tip of Mt. McKinley, and even on the International Space Station.

A pound is a unit of mass. Perhaps you are confusing the pound with the pound force.

19. Dec 26, 2012

### Staff: Mentor

No it doesn't. That was berke making fun of our physicist friends:
http://en.wikipedia.org/wiki/Escape_velocity

20. Dec 26, 2012

### Jimmy Snyder

Try down. That's a direction.