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View Full Version : "4 million lbs. of energy"--huh?

Usurer
04-22-2001, 05:01 PM
A Sunny Delight commercial maintains that the sun creates 4 million pounds of energy per second. Now, I only had one year of college physics, but I'm pretty sure "pounds" is the unit for weight, and energy would be measured in calories or joules or something. Did this company spend millions of dollars to look like idiots on national TV?

El Marko
04-22-2001, 05:58 PM
Yeah, Pretty much. The sad thing is that 99% of the people who will watch that commercial are so mathematically and scientifically ignorant that they won't notice the error.

Akatsukami
04-22-2001, 06:11 PM
Actually, I think it's 4 million tonnes of energy per second. That's the amount of mass converted to energy via the p-p chain.

kanicbird
04-22-2001, 07:04 PM
lets not forget E=mc^2. Energy is mass

Blowie
04-22-2001, 07:43 PM
If they said “kilograms” which is a unit of mass, they might have a leg to stand on. But come on folks – “pounds”? A unit of weight which is dependent on where it is? How much does it weigh in space?

Ok, they meant the equivalent of here on earth. But its on the sun.

Sorry, I get up like this when mass and weight are treated as the same thing.

barking frog
04-22-2001, 07:54 PM
I was thinking about posting the exact same thing, but then I read Akatsukami's reply which said it was tonnes - I just assumed the OP made an error.

RyanD004
04-22-2001, 09:41 PM
Well, technically.. isn't pounds a unit of force over area. I may be wrong, but i always thought of it as an outdated way of measuring force. Essentially it's and acceleration per amount of mass. Still the whole conversion process from joules to pounds seems annoying and pointless.

OldMan
04-22-2001, 10:08 PM
Ah, the wonderful imprecision of human languages. Be a good test of how fast I can type, to get this posted before a real physicist shows up to straighten this out.

The confusion mostly arises because in common usage, pounds and kilograms are generally taken to be measurements of the same thing, as in "a kilogram is 2.2 pounds," so we say a person who weighs 150 pounds also weighs 60 kilograms. But on the moon, that person weighs about 25 pounds, but is still 60 kilograms. Pounds are a measurement of force, kilograms are a measurement of mass. (RyanD004: force over area is pressure.) We go back to the great grandaddy of all physics equations, Sir Isaac Newton's F=ma, force equals mass times acceleration. Mass in kilograms, acceleration in meters per second per second, gives you a force unit called, sensibly enough, the newton. Pounds are equivalent to newtons. The appropriate mass unit if you're going to use pounds as the force unit is (get ready for it...) slugs. No wonder we don't use the term.

Chronos
04-22-2001, 11:55 PM
OK, it's 3.826*1033 erg/s. That's 3.826*1026J/s, and using e=mc2, that works out to 4.257*109 kg/s converted, which is a bit over four million (metric) tons. Note that a metric ton is a thousand kilograms, and is hence a mass unit, wheras an American ton is two thousand pounds, a weight unit.

jmonster
04-23-2001, 01:06 AM
Originally posted by OldMan
pounds ... kilograms ... newtons ... slugs

So where do stones enter into it?

Dijon Warlock
04-23-2001, 02:32 AM
Maybe they meant pounds sterling. What's the going rate for electricity in the UK these days?

Hey...I tried...

Akatsukami
04-23-2001, 06:33 AM
Originally posted by Blowie
If they said “kilograms” which is a unit of mass, they might have a leg to stand on. But come on folks – “pounds”? A unit of weight which is dependent on where it is? How much does it weigh in space?

Ok, they meant the equivalent of here on earth. But its on the sun.

Sorry, I get up like this when mass and weight are treated as the same thing.
Yeah, I feel your pain. But nobody, nobody, will ever tell you that they're going to the store for 5 newtons of broccoli1, not even ESA engineers; they'll say that they're going to get half a kilo (although they'll measure it by weight, not by mass). They'll never say that they're going to get 1/32 of a slug (a tip of the beer bottle to OldMan), either.

When the average person who watches commercial TV is reasonably conversant with situations where weight varies whilst mass remains constant, commercials and textboks wil likely change their wording so as not to look too stupid (I'm being optimistic here). Until then, we'll have to deal with it.

1Yes, I know; the conversion factor isn't 10 newtons = 1 kg at standard acceleration. Close enough, though; I refuse to act like Lloyd George.

Blowie
04-23-2001, 09:11 AM
True. No one wants a slug of broccoli or put up with a newton of Fig Newton jokes. But there is nothing horrendous about getting a kilo of food. (short for kilogram)

Not that I would know, but I understand that is how drugs are sold.