Weight/Elevations
by Nettacow on 06/02/04 at 17:31:10

This site rules!  Can anybody tell me what will happen at 7,400 feet to a bag of corn that weighed 50 pounds at 3,200 feet?

Real life application - the bag is filled at location A (3200) and shipped location B (7400).  When B weighs it, are they getting more or less than they paid for?  I'm thinking less (gravity not as strong?), but I'm too far out of a physics frame of mind to prove it.

Thanks!

Re: Weight/Elevations
by Robert Fogt on 06/02/04 at 22:51:40

The difference in weight will be so small as not even measureable.

Your weight is determined by your mass, Earth's mass, and the distance from the center of Earth to your center.
F = Mm/r[sup]2[/sup]

In your example, your mass and Earth's mass stays the same, only distance changes. But since Earth is 12,756.3 km in diameter, with a mass of 5.972e24 kg, such a small distance of 4200 feet and small mass of 50 pounds of corn wont make much of a difference.

Re: Weight/Elevations
by Robert Fogt on 06/02/04 at 23:17:32

Here is a link that answers your question much better.

[url]http://www.madsci.org/posts/archives/aug98/901745222.Ph.r.html[/url]

Re: Weight/Elevations
by Albert on 06/06/04 at 10:37:19

It is not the earth's gravity that influences the weight measurably at diffrent altitudes, but it is the air density that matters.

At sea level an object has an upward  force from the air it is surrounded with. It floats a bit on air.

As you get higher the desity of the surrounding air decreases (due to the reduced pressure) so the upward force acting on the object decreases also, so the object will weigh less at high altitudes than at sea level.

This diffrence is so small that you don't have to worry about that in normal circumstances.
But if you want to calibrate for instance an analytical balance at an high altitude with calibration weights, you have use a correction factor for this phenomena.

You can calculate the magnitude of this effect:

(density air loc 1 - density air loc 2) X volume of weighted body = weight diffrence

More about this:
http://www.npl.co.uk/mass/faqs/miscellaneous.html


Albert

Go Back | Archive Index