Units at the Science Museum

While in Alabama this past weekend, I visited the Birmingham science museum, called the McWane Science Center. It was a fun diversion for me, especially since the first floor of the museum was essentially all physics toys. Sadly, I discovered some problems with units on a couple of the displays, so I sent this letter to the museum:

I visited your museum this past weekend and really enjoyed your exhibits. I think you have developed a nice set of hands-on exhibits which are both fun and educational.

Being a physicist, there were a couple problems with signs that I wanted to bring your attention.

First of all, on your combustion engine display there is a sign explaining the origin of "horsepower". This sign says that one horsepower is equal to: 33,000 lbs per ft / 1 minute

Unfortunately, lbs / ft / minute is not a unit of power. The correct units are ft. lbs. / minute (distance * force = energy, then energy / time = power). Or to be more explicit about the problem, pounds should be multiplied, and not divided, by feet.

The other thing I noticed was also an issue with units. In the IMAX theater you have an introductory sequence which shows the audience the speakers and screen (this sequence is very cool, by the way). At one point in the sequence a claim is made to the effect of: "resolution of 2,400 CD-ROMs". Last I checked, a CD-ROM was not a unit of resolution. It also does not make sense to refer to the amount of information storable on a CD, as the resolution of such an image depends on the encoding.

Perhaps what you mean is to compare to the resolution of a video CD (which is half the resolution of VHS or DVD video, an odd standard to compare to). In that case, your number also does not make sense.

To properly digitize IMAX film requires scanning the negative with 8,000 horizontal lines of resolution (and a similar number of vertical lines... this is referred to as 8K resolution in the movie industry). A video CD has 240 lines of horizontal resolution. If we are just comparing horizontal lines, then, we have 8000 / 240, or roughly 33. Obviously, this is a far cry from 2,400.

I think of I have gone off far enough in my digression, so I'll stop there.

Thanks for reading.


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