Fourteen pounds

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Sac Arrow

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Is a British Stone. But... all the references I've come across are ambiguous as to whether it is a measure of weight, or mass. Some say it's a weight. Some say it's a mass. Since it's defined as being fourteen pounds (presumably lbf not lbm) by conjecture it should be a weight.

Anyone know definitively?
 
A gram is in a unit of mass. Mass does not change.
Pounds, stones, ounces are units of weight. Weight changes with its location relative to another mass.
 
Morgan3820 said:
A gram is in a unit of mass. Mass does not change.
Pounds, stones, ounces are units of weight. Weight changes with its location relative to another mass.
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I was waiting for someone to point this out. :)

As long as the things being compared are on earth, weight and mass are effectively the same thing.
 
Morgan3820 said:
A gram is in a unit of mass. Mass does not change.
Pounds, stones, ounces are units of weight. Weight changes with its location relative to another mass.
Click to expand...

There are two different pounds. Pound mass and pound force.

So when you say pound it could be either weight or mass. It’s ambiguous.
 
skier said:
There are two different pounds. Pound mass and pound force.

So when you say pound it could be either weight or mass. It’s ambiguous.
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And don't forget the currency.
 
skier said:
There are two different pounds. Pound mass and pound force.

So when you say pound it could be either weight or mass. It’s ambiguous.
Click to expand...

Normally if you don't specify it is assumed you are talking about lbf. We don't even like to use lbm in calculations involving mass and acceleration because it is too easy to confuse the units.

Morgan3820 said:
I’m sorry, thought I was trying to help. Sounds like you answered your own question.
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Nope, I didn't answer my own question. My question was whether a stone was a mass or a force, not the difference between force and mass.
 
donjohnston said:
As long as we're on earth, mass and weight are synonymous. But if you are on the moon, that 14 pound brick (weight or mass on earth) will weigh 2.3 pounds. But its mass will still be 14 pounds.
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Well... it would be correct to say 'it's mass is 14 pounds mass' but it it's not 14 pounds force, which is generally assumed unless explicitly specified otherwise.

A pound mass is a secondary unit of mass which is one slug numerically divided by 32.2.

This is one example where SI units are much less confusing. One kilogram weighs 9.8 newtons. Period. There is no 'newton mass' with the gravitational constant divided out to confuse the issue.
 
Sac Arrow said:
Well... it would be correct to say 'it's mass is 14 pounds mass' but it it's not 14 pounds force, which is generally assumed unless explicitly specified otherwise.

A pound mass is a secondary unit of mass which is one slug numerically divided by 32.2.

This is one example where SI units are much less confusing. One kilogram weighs 9.8 newtons. Period. There is no 'newton mass' with the gravitational constant divided out to confuse the issue.
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I'll tell you what's confusing; When someone posts a question because they don't understand something and then gets pedantic with an answer.
 
Sac Arrow said:
he actual base unit of mass in the English system is the slug.
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Or, the pound mass.

The actual NIST legal definition of the "pound" in the U.S. is 0.45359237 Kg exactly.

donjohnston said:
As long as we're on earth, mass and weight are synonymous. But if you are on the moon, that 14 pound brick (weight or mass on earth) will weigh 2.3 pounds. But its mass will still be 14 pounds.
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If you "weigh" the brick using a balance you will get 14 pounds.

balance-weight-scale-500x500.jpg


Like the "Stone" the "Pound" predates Newton's laws of motion and gravity and thus does not have an unambiguous definition. When I was an undergrad, everything was in terms of pounds mass, pounds force. What I teach now (well, up to a couple weeks ago...) is slugs, pounds force. What I have never used as an engineer in industry are slugs.

 
donjohnston said:
As long as we're on earth, mass and weight are synonymous.
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The precision lab balances I’ve been buying to equip some new labs specify that anytime they are relocated more than two floors up or down from where they were first installed, they need to be recalibrated. Changing the distance from the earths center by even that little changes the force of gravity enough to affect them. Or so Mettler-Toledo claims.
 
Sac Arrow said:
This is one example where SI units are much less confusing. One kilogram weighs 9.8 newtons. Period. There is no 'newton mass' with the gravitational constant divided out to confuse the issue.
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No, but kgf (kilogram force) is commonly used.
 
See, this is why I stick with Euclidean geometry and Newtonian physics. Those are already brain-hurting enough. Quantum stuff? Relativity? I can't taste them, so . . .
 
Dana said:
No, but kgf (kilogram force) is commonly used.
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Where have you seen that out of curiosity? The only alternate force unit I’ve seen in SI is the Dyne for those physicists who love CGS over MKS. Wiki lists the kgf as largely deprecated.
 
AKiss20 said:
Where have you seen that out of curiosity? The only alternate force unit I’ve seen in SI is the Dyne for those physicists who love CGS over MKS. Wiki lists the kgf as largely deprecated.
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"It's a joke, son."
 
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