Welcome to your weekly dose of TRC! Adam kicks things off by addressing a syndicated column filled with anti-vaccine misinformation and pseudoscience that was recently published in the Toronto Sun newspaper. “Physics Commando” Barry Panas schools us about errors in school textbooks after hearing a recent episode where Darren cites the Earth’s mass. Finally, Pat drops a bombshell on the panel with a segment everyone should hear regarding passwords and how to find out if you’ve been compromised without even knowing it.
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Recent Anti-Vax Article
Vitamin C: Do High Doses Prevent Colds? – Quackwatch
Antivaccine propaganda from Dr. W. Gifford-Jones in The Toronto Sun – Science Based Medicine
Toronto Sun newspaper pulls column skeptical of vaccines after backlash – CP24
Toronto Sun: Facts Matter More Than Opinion
The Cyberwire – Hacking Humans Podcast
I’m a bit surprised that none of you knew about the Megabyte vs. Mebibyte (etc.) thing (though not at all surprised that you don’t use them). If you’ve ever dropped a lot of money for a huge hard drive and then noticed that Windows didn’t report the advertised number of “megabytes” on it, you should have checked the fine print: besides accounting for filesystem overhead, most manufacturers advertise in mega/giga (base-10 type) numbers, not mebi/gibi (base-2 type) numbers – so a 1.0 Tebibyte drive can usually be sold as a 1.1 Terabyte drive (“a whole 100 gigabytes more!”), etc. Sure, it is marginal, but it has always allowed them to round up.
(Back in the early ’90s when ISDN (Integrated Services Digital Network) was supposed to be the future of digital communications, telecom people were always *very* eager to point out the difference to me, but I still never used those prefixes: honestly, it would talk too long to convince anyone that it was the correct set of terms… and they still wouldn’t use them because it sounds too much like babytalk.)
I think it is worth pointing out that this is a redefinition. For many many years there was never any suggestion that kilobyte meant anything other than 1024 bytes. It was only in relatively recent years at the urging of the hard drive manufactures that IEEE accepted that kilo should follow the standard metric definition of 1000 and developed the kibi byte as an alternative and maintained the standard abbreviations. Obviously nobody in industry has ever accepted the metric definition of kilobyte and outside of HD manufacturers I don’t think I’ve ever seen it used. I don’t think there is any movement in the field to actually use the metric abbreviations.
In the FPS system, a pound is a unit of force. The unit of mass is the slug. It was disappointing to hear you sound so certain of something you were exactly backwards on.
Hi Eric. Thanks for your post. I’ll try to clarify and back up my claim about the pound being a unit of mass. Warning: this is excessively confusing, so I’m going to start with a “summary” and then move into details:
The “pound” (lb) is very much a unit of mass: https://en.wikipedia.org/wiki/Pound_(mass)
The “pound-force” (lbf) is a separate unit, and is a force unit. The pound-force is often mistakenly confused with the pound. Notice in the wikipedia page that you linked to, the “pound” is actually the “pound-force” (lbf).
Here is a link to NIST (US National Institute of Standards and Technology) in which units are defined. Click the link near the top of the page for “MASS and MOMENT OF INERTIA” to find the pound listed a mass unit which is, in fact, defined in terms of the kilogram.
You are correct that the slug is a unit of mass, but you are not correct about it being the unit of mass in the FPS system. In the FPS system, the pound actually is the unit of mass. The slug is, however, the unit of mass in the BG system, which is a variant of the FPS system:
Confusion arises from there being a completely separate unit which is properly known as as a “pound-force” which is abbreviated “lbf” (whereas a “pound” is abbreviated “lb”). For what it’s worth, there is also a force unit which is called a “kilogram-force” (kgf) which is the exact analog of the lbf. And if all of this isn’t confusing enough, there is ALSO a unit called a “poundal” … which is the force needed to give a mass of one pound an acceleration of 1 ft/s^2.
Hope that helps.
Pound has historically been used for both force and mass. Both are correct. This is ambiguous and therefore for clear communication it is often considered good practice to qualify the pound force when you are talking about force. However, I think it is extremely misleading to say that is the “official” definition. In engineering when working in FPS we pretty much always use pound to refer to force (lbm is an ugly unit to work with).
An interesting note is that for the most part we measure force and infer mass.
The one thing I think we will all agree on is SI is much much easier to work with.
Hi James. I tried to keep my response short but failed. Sorry!
I agree with the historical pound being ambiguous, so to be clear, I am only discussing the pound as a modern unit. I am assuming (?) that you would not advocate for the use of a foot (unit of length) based on historical uses that differ from the modern foot, which is actually defined in terms of the meter.
You stated that “In engineering when working in FPS we pretty much always use pound to refer to force ”. I have no problem with that, but I maintain that the pound is nonetheless “officially” a mass unit. Whether certain common practices accepts or rejects this is a separate question (apparently with an answer of “rejects” at least some of the time).
Of note here is my use of the word “official,” which appears to be the point that you don’t agree with, based on your stating that it is “extremely misleading to say that [pound as a unit of mass] is the “official” definition”. To be clear, I am basing my “official definition” on literal “officiating” (i.e. authoritative) bodies. It is objectively true that the following bodies define or recognize the pound as a mass unit (with 1 lb being approximately equal to 0.454 kg):
– the International Bureau of Weights and Measures
– the National Institute of Weights and Measures (USA)
– the Government of Canada (the only government that I specifically looked into)
– the Institute of Electrical and Electronics Engineers
Deciding whether or not the above should be recognized as being “official” is subjective. Personally, I subjectively recognize the above to be authoritative on this matter, and so maintain the pound is “officially” a mass unit. Anyone who disagrees with this should recognize that they are subjectively choosing to disregard the authority of the above. If that is your position, then we subjectively disagree on what qualifies as “official”. Being subjective, I think we’d have to agree to disagree, and I have no problem with that. Thankfully yes, we do agree that SI is much easier (and less prone to this kind of confusion).
Here’s another fun one for you: how about the BTU? A unit of energy, or of power? My short answer is that it depends on who you ask, and also on how you ask.
I don’t think any of that disproves that pound can also be a unit of force in addition to being a unit of mass. You say that pound-force is a separate unit, but I think you are misunderstanding the use. Pound-force (or pound force you will see both) is just a way of writing pound to be clear and is not intended as a different unit. The most clear demonstration of this is the common measurement of pounds per square inch, which is never written as pounds-force per square inch even though they would virtually always be talking about force.
As for BTU I always understood the definition to clearly be energy (amount of energy needed to raise 1 pound of water 1 degree farenheight). I think using BTU for power is just simplifying BTU/hour to BTU as a shortcut not as a real unit.
Your “most clear example” of psi is the opposite of what you claim, as psi really is pound-force per square inch(!) Your claim that it “is never written as pounds-force per square inch” is wrong.
“pound-force per square inch (psi) (lbf/in^2)”
“The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in^2)”
As for BTU, I agree with you, but try talking to someone who works in HVAC (or Home Depot etc.). There is a very good chance that they will claim the BTU is a power unit, with one of “their BTU” being what you and I would call a “BTU/h” (and to be clear, there is a good chance that they will have no idea about the “per hour part”. Despite this “common usage” I agree with you that BTU is officially an energy unit, and common usage does not change that.
Well that is interesting, I am pretty sure I have never seen it written as lbf/in^2 in my life (I’m going to start looking for that though). I guess NIST has decided to be pedantic about differentiating the concept of pound-force. Perhaps things change, and I’m just an old engineer who isn’t keeping up, but I’m pretty sure this usage is still quite limited.
I still don’t think that it makes it “official” and if you were to teach only this definition you wouldn’t be doing your students any favours. So I guess we are probably back to agreeing to disagree.