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Earths magnetic forces question.

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PAUL161

PAUL161

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Due to the circulation of earths magnetic forces, (if the earth is round), would an object weigh more or less at the North pole verses the South pole? I guess it wouldn't work if the earth is flat! :highly_amused:

Lets say you weigh an object at the equator and it weighs 200 lbs, would it weigh the same at the poles? Just a thinker question. :devilgrin:
 
https://en.wikipedia.org/wiki/Gravity_of_Earth

"In combination, the equatorial bulge and the effects of the surface centrifugal force due to rotation mean that sea-level effective gravity increases from about 9.780 m/s2 at the Equator to about 9.832 m/s2 at the poles, so an object will weigh about 0.5% more at the poles than at the Equator.[3][7]"

This suggests a geometrical variation in gravity, not a variation based on dynamic motion of the fields.


It is worth mentioning that the childhood story we were told about Columbus being warned he would sail off the ends of a flat earth is a total fabrication. It can be blamed on the biography of Columbus written by Washington Iriving and perpetuated by John William Draper. Pundits had agreed for centuries that the earth was round with the issue of dispute being the size of the sphere.
 
Another way to look at it - "weight" is just an arbitrary measurement taken at a specific location. So that 200 pound object still "weighs" the same anywhere it's located. Its mass never changes.

But the "measurement" of the mass will vary, depending on the location where the measurement is taken, and the circumstances of the device doing the measurement. A common scale at -60°F will likely read differently than the same scale at +60°F, because its physical characteristics have changed.

OK - back to my cave.
Tom M.
 
But "weight" isn't the same as mass; weight is the measurement of attraction between two bodies (with the earth usually being one of the bodies). So, for example, we call objects outside a gravity field "weightless" even though they clearly have mass.

There are actually small variations in the force of gravity all over; including (IIRC) a small difference between north & south poles. Some of our customers used to run around measuring the force of gravity, using a device called a gravitometer (or gravimeter). At one time, maps of the variation were actually used as navigational aids for submarines!

Here's one such map, rendered in pseudo-color. The more reddish colors represent lower force of gravity, usually because of elevation changes
cont_northamerica_large.jpg


But the original question was about magnetic fields, which are different than gravity. The magnetic field does vary with time; but not by very much and hardly what I would call "swirling". The magnetic lines of force above the surface are more variable, since they are influenced by the solar wind. And since many materials are not affected by magnetic fields (try picking up sand with a magnet), any discussion of the effect on weight has to include what material we are talking about.
 
Who remembers from physics class the formula F=ma If F= weight, then mxa = mxg. This makes w/g=m ! Weight and mass are not interchangeable words. Le T.
 
Variances in the magnetic field will have no material affects on the weight of an object. As it was pointed out above weight is simply a measure of attraction between two objects with mass, in this instance the earth and the objects upon it, so only variances in gravity will affect weight.
 
NutmegCT said:
But the "measurement" of the mass will vary, depending on the location where the measurement is taken,
Click to expand...

You have that backwards. If you don't alter the item you are talking about, its mass is constant. Its weight is its downward force due to gravity. Its weight will change as gravity changes. It goes back to F = M x A as 2Liter said earlier. F = force = weight, a = acceleration = gravity. Mass is a constant.
 
dklawson said:
You have that backwards. If you don't alter the item you are talking about, its mass is constant. Its weight is its downward force due to gravity. Its weight will change as gravity changes. It goes back to F = M x A as 2Liter said earlier. F = force = weight, a = acceleration = gravity. Mass is a constant.
Click to expand...

Thanks Doug. Maybe I'm missing something. I never said the mass changes - I said the measurement changes.

Tom M.
 
Unless there were a large iron content in the mass being weighed, the variation would be small to the point of being inconsequential (as Doug's post stated, 0.5%).

Doug said:
This suggests a geometrical variation in gravity, not a variation based on dynamic motion of the fields.
Click to expand...
:thumbsup:
2litre4cyl said:
Weight and mass are not interchangeable words
Click to expand...


IOW: not equivalent. As a "tween" this was one of my Ol' Fella's teaching points. As one example he "weighed" a sugar cube and an equally sized piece of stainless steel, leaving it to me to describe the reason for the variation.

By that time we had been knee-deep in "All About" books, too.

 
I suspect the problem is that weight is a much more easily measured property than mass; and for most people remains constant enough that we tend to think of them interchangeably. To add even further to the confusion, we use the same units for both.

But I wouldn't call weight a measurement of mass, any more than top speed is a measurement of horsepower. They are closely related for sure, but other factors are involved in the relationship.
 
Well, generally speaking ...

"I know you think you understand what you thought I said but I'm not sure you realize that what you heard is not what I meant.”

often attributed to Alan Greenspan
 
TR3driver said:
To add even further to the confusion, we use the same units for both.
Click to expand...

Certainly true. However, if you are asked to do engineering calculations with mass and force, you would use pounds for force and "slugs" for mass (in SAE units). Metric is not that much better with kg being used for mass and Newtons for force (weight). I've never heard a European specify their weight in Newtons, it's always kilos.

Back when I was in engineering school I prefered to make calculations in metric. It was somehow easier to keep those straight in my head. I still don't have a good feel for "slugs".
 
dklawson said:
Back when I was in engineering school I prefered to make calculations in metric. It was somehow easier to keep those straight in my head. I still don't have a good feel for "slugs".
Click to expand...
But it's so simple! A slug is defined as the mass that accelerates at 1 foot per second per second when a force of 1 pound-force (lbf) is applied.
:D
 
Glad I awoke at midnight and stumbled on this thread while waiting for somnolence again. This stuff always put me to sleep in college and I hope it will work now.
Bob
 
GregW said:
I've never seen a slug accelerate that fast, even when I put salt on them as a kid.
Click to expand...

You're not hanging around the right kind of bars then. A slug of Scotch accelerates at 32 ft/sec2 as it's poured into a glass.
 
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