Why Does Weight Depend on Location?

[chito1]

Homework Statement

Vacuum height of mercury

Relevant Equations

Is the pressure in kg / cm2abs when the vacuum height of mercury is 36cmHg?
Is the pressure in kg / cm2abs when the vacuum height of mercury is 36inHg?
Is the pressure in kg / lb/ni2abs when the vacuum height of mercury is 36cmHg?
Is the pressure in kg / lb/ni2abs when the vacuum height of mercury is 36inHg?

Vacuum height of mercury

 

[berkeman]

Whaatt?

What's an ni2abs? Can you please define your units, and show the unit conversions that are probably involved? Thanks.

 

[haruspex]

Homework Statement:: Vacuum height of mercury
Relevant Equations:: Is the pressure in kg / cm2abs when the vacuum height of mercury is 36cmHg?
Is the pressure in kg / cm2abs when the vacuum height of mercury is 36inHg?
Is the pressure in kg / lb/ni2abs when the vacuum height of mercury is 36cmHg?
Is the pressure in kg / lb/ni2abs when the vacuum height of mercury is 36inHg?

Vacuum height of mercury

I assume ni2abs should be in²absolute.
kg / cm² is not a pressure. You probably mean kg wt/ cm². Metric units don't play fast and loose with masses and weights like the American system does.

Regardless of the units used for the height of the mercury, you can use whatever units you like for the pressure. It's just a matter of making the necessary conversions.

If you are asking what units you would use for pressure in order to avoid or minimise conversions, the answer depends on the units you have for the density of mercury. E.g. if that is given as 13.56 grams per cubic centimeter, then a height of y cm of mercury will exert a pressure 13.56y grams wt per sq cm, or 0.01356y kg wt/cm².

If you have a specific case in mind, please post it.

 

[rude man]

Metric units don't play fast and loose with masses and weights like the American system does.

Then how come the metrics world quotes weight in kilos whereas the yankee system correctly uses pounds?
And no, no one says "I weigh 80 Newtons"!

 

[jbriggs444]

Then how come the metrics world quotes weight in kilos whereas the yankee system correctly uses pounds?
And no, no one says "I weigh 80 Newtons"!

The "yankee system" is ambiguous about whether pounds means mass or force.

Legally, medically, for purposes of commerce and for purposes of how fat you are when you stand on a scale, pounds are units of mass. Most of the time when we yankees think about the pound, we think of it as a unit of force. One cannot be correct about how a unit is used if one is ambiguous about how that unit is used.

When we say that we "weigh 80 kilograms" that is entirely proper and is a claim about our mass. Even though your physics teacher will ding you for using the word "weight" to denote a mass. Your physics teacher is paid to teach you a jargon usage of the term. That does not preclude the correctness of other meanings.

 

[rude man]

When we say that we "weigh 80 kilograms" that is entirely proper and is a claim about our mass. Even though your physics teacher will ding you for using the word "weight" to denote a mass.

Weight depends on where you are.
If your "weight" is 80kg on Earth it is much less on the Moon. So on the moon your scales give you your incorrect mass. Your scales give you your mass on Earth only. Your "weight" should be denominated in Newtons, not kg.

 

[jbriggs444]

Weight depends on where you are.
If your "weight" is 80kg on Earth it is much less on the Moon. So on the moon your scales give you your incorrect mass. Your scales give you your mass on Earth only. Your "weight" should be denominated in Newtons, not kg.

The "net weight" on a 16 ounce can of peas is 16 ounces regardless. At the equator. At the poles. In Death Valley. On Mount Everest, on the moon and in orbit. That "net weight" is a mass measurement. By law. Exactly as we would want. We would not want to buy and sell goods using a measurement that depends on location.

A Toledo scale will give you the same answer for all of those except, possibly, in orbit. "Honest weight, no springs".

A spring scale will also give you the same answer, provided it is valid for commercial use. Such a scale will have been properly calibrated to deliver correct mass measurements in the location where it is used.