Unappropriate velocity unit - km/h

[jiri]

Velocity unit of km/h is suitable for passengers, cars and planes. In astronomy, instead, the SI unit (k)m/s should be standard. In the picture text, values of >500000 km/h are used - crazy numbers, too many zeroes. Should the many zeroes impress the innocent laymen? I guess, they are confusing instead of informing. Cheers, Jiri

[Chris Peterson]

Velocity unit of km/h is suitable for passengers, cars and planes. In astronomy, instead, the SI unit (k)m/s should be standard. In the picture text, values of >500000 km/h are used - crazy numbers, too many zeroes. Should the many zeroes impress the innocent laymen? I guess, they are confusing instead of informing. Cheers, Jiri

The captions aren't written for astronomers or scientists, though. So using familiar units makes a lot of sense. I think the average person has a better feel for 500,000 km/h than they do for 140 km/s.

In general, I like to see units given in both the conventional scientific form as well as a parenthetical conversion to more widely used units when appropriate. That serves both clarity and education.

[JohnD]

Don't agree, Chris! I don't think that "the average person has a better feel for 500,000 km/h than they do for 140 km/s".

No one has a mental handle for 500,000kms, unless like you they are an astronomer.
But everyone who can think in kms or can convert them to miles will realise, gosh, my brother John lives in Atlantic City, Marseilles, York or Foggy Bottom(say) and that's only 140kms (90mls) away.
There in one second! That's fast!

John

[jiri]

You are right, JohnD. I wrote the suggestion because I have been teaching >7000 US students in Europe over 40 years and know that what you call "a mental handle". Yes, objects outside Earth may be fast and more people should better understand them. I am new in SA (Star Asterisk): how to let the picture text author know about this subject?
Jiri

[geckzilla]

You can find their email addresses at the bottom of this page:
http://apod.nasa.gov/apod/lib/about_apod.html

And, personally, meters and kilometers make no sense to me. Better put it all in yards and miles. Or, better yet, football fields!

-Typical American
Just kidding.

[neufer]

Don't agree, Chris! I don't think that "the average person has a better feel for 500,000 km/h than they do for 140 km/s".

No one has a mental handle for 500,000 [km/h], unless like you they are an astronomer.

I agree wholeheartedly!

Multiple zeros should be avoided whenever possible regardless of the method used.

Everyone should be able understand that 140 km/s is rather fast as compared to most motions in the solar system
but very slow as compared to the speed of light.

500,000 km/h is just a funny sounding number that nobody can relate to
(and the "km/h" often gets lost in the relative small print).

NGC 2736: The Pencil Nebula

Explanation: This shock wave plows through space at over 500,000 kilometers per hour.

140 km/s is, in fact, not an untypical sort of particle/sound velocity for a million degree hydrogen plasma.

Our own supersonic solar wind has a velocity of ~ 400 km/s.

500,000 km/h does not help in any way in getting a physical grasp of what is actually taking place.

[Wombat]

"In general, I like to see units given in both the conventional scientific form as well as a parenthetical conversion to more widely used units when appropriate. That serves both clarity and education."

I agree 10.2E9 times.

[owlice]

Don't agree, Chris! I don't think that "the average person has a better feel for 500,000 km/h than they do for 140 km/s".

No one has a mental handle for 500,000 [km/h], unless like you they are an astronomer.

I agree wholeheartedly!

I don't, but then, I'm more like the average person than you are.

Multiple zeros should be avoided whenever possible regardless of the method used.

Disagree. Multiple zeroes are okay in many contexts, including this one.

[Chris Peterson]

Don't agree, Chris! I don't think that "the average person has a better feel for 500,000 km/h than they do for 140 km/s".

No one has a mental handle for 500,000kms, unless like you they are an astronomer.
But everyone who can think in kms or can convert them to miles will realise, gosh, my brother John lives in Atlantic City, Marseilles, York or Foggy Bottom(say) and that's only 140kms (90mls) away.
There in one second! That's fast!

I face this situation frequently in discussing meteoritics. A typical meteor is traveling about 50 km/s. In speaking before American audiences, and in the classroom, I find that very few people have a good concept of what this means. Converting to miles is some help, but even 30 miles/s just doesn't make an impression with most people, unless I actually frame it as you do: give a pair of cities and point out that the meteor would travel between them in a second. Most people don't make that connection themselves. But they do seem to get 115,000 mph, even though the number is large. And in giving interviews to newspapers or on TV, I'm always asked what km/s is in miles per hour.

The reality is, most people are generally more comfortable with familiar units, even when the value itself is an unusual one. And that's why I think the best approach is to use both.

[bystander]

I think people making complaints should use appropriate verbiage. I'm not even sure unappropriate is even a word, although unappropriated is.

[jiri]

I think people making complaints should use appropriate verbiage. I'm not even sure unappropriate is even a word, although unappropriated is.

Thank you for improving my English, perhaps better would be "unsuitable". I am sorry that my suggestion could be understood as a complaint - that was not my intention.
Jiri

[JohnD]

Chris has lectured to more people that I have!
If he finds that people are easier with the kms or miles per hour, than km/m per sec, then he's right!

So lets have both?

geckzilla may be interested to know that in the UK, the metric system has been taught in schools for a generation and we use it for weight, of foods for instance, and our weather forecasts give temperatures in Celcius, but not for distance. It's still miles between towns, for speed limits, and for wind speed!
Bizarre, I know, but that's British compromise for you!

John

[neufer]

Multiple zeros should be avoided whenever possible regardless of the method used.

Disagree. Multiple zeroes are okay in many contexts, including this one.

I have an odd urge to throw oodles of ooids or oolites oozing oily oleo over at an old owl.

[Beyond]

Uh-Oh, i hear the sharpening of pointy-grabby things.