I just realized that I made the second reference to Monty Python birds in this thread. Eerie.
Aren’t we measuring the weight of the planet with all it’s stuff on it? People must add significantly to the weight. Then there’s the other animals. The buildings, the cars, the boats, the airplanes (not flying). Why even all the cockroaches in the world must add some weight. I’ve seen some around here that weight at least half a pound.
I propose that we at least take the human element out. Mjollnir, you get ready with the scale on your head. On your signal, all five billion of the rest of us will jump up. At that moment, check the scale. Then subtract your own weight (you can’t jump with the scale). Then we’ll know the weight of the Earth without us people on it.
Just make sure your signal is big enough so the folks in the back can see it. Thanks for your help.
No, no. The people will cancel themselves out. See some are pushing agaist the scale…they are the ones on the other side of the planet.
Then some on your side…they push with the scale.
Everything cancels out, leaving just the earth.
The ziplock idea is just stupid…air doesn’t way anything. :rolleyes:
It seems to me that we are using a word in its own definition. If weight is defined by gravity and you separated a portion of the earth to weight it individually from the rest, you have reduced “the rest”, the earth and therefore the piece you are weighing is going to weigh less than if you could weigh the same piece on a complete earth.
This made more cohesive sense before I started typing it out.
Also, what is the relation between the centripedal force of the planet spinning and the gravity that keeps it together, as well as keeping, at least some of us, “firmly grounded”?
And, place the scale on the ground over a hole and use a mirror to see the reading.
air doesn’t weigh anything?
say that when someone drops a ton of liquid oxygen on your toe
why I just happen to have a ton of liquid oxygen right here,
…oh, must have left it in my other pants
Oh, ZenBeam, I concur with you. What an idiot I feel like. Will someone kindly tattoo on my forehead the fact that density is mass per unit volume, not per unit radius?
And MisterJackPunch, air does too have a zero weight. You only think it weighs something because when you condense oxygen, or any of the other atmospheric gasses, to a liquid, you take out all the “empty space” in between the molecules, which has a negative weight. When you extract this empty space from the air, it shoots up (because of its negative weight, get it?) into the atmosphere, so you never see it.
Thank you MisterJackPunch for the weight of air comment.
And as for centripetal force fling us away from the planet, it is absolutely minute in relation to the gravity that holds it down, but if you want to figure its exact amount…
Hold on–I used to know this equation off the top of my head. Just let me go derive it quickly…
centripetal (centrifugal?) force for an object traveling in a perfect circle is equal to:
speed squared divided by the radius of the circle
OR
s * s / r
where s = current speed along the circumference
and r = radius
Applying this to the dimensions of the earth at the equator, we get:
Centripetal force = 0.033722 meters per second per second contrasted to the nearly 10 of gravity pulling in the opposite direction.
[An interesting exercise using this formula is to figure out how high one needs to be for centripetal force and gravity to exactly cancel each other out. Find that, and you’ll have the height for geostationary orbits.]
the empty space does not have negative weight
it has zero mass, that is to say no weight
and of course air does not have a zero weight
from our perspective it may have a Negligible weight
but every molecule, every atom has weight
hydrogen is not weightless, it is simply less dense than the chemical soup that makes up our breathing air
Pizzle Boy, air does too have weight. That’s why it clings to the Earth and doesn’t float away, leaving earth an atmosphereless hunk of rock. Air’s weight happens to be very small per unit volume, but it is there.
Empty space does not have negative weight, it has zero weight.
Thanks, Son Tinh
Wouldn’t that centrifugal/centripedal force formula have to include the momentum of the object?
ie marble spinning on a string/bowling ball spinning on a string
and, I was refering more to the centripedal force pulling the crust of the earth away, as opposed to pulling us away
when people ask me how it’s going, I say it’s going, and as long as it keeps going we’ll all be okay
btw, I, also, am very interested in reading this article(?) about the inequality of earth’s weight, or whatever it purtpors to say, assuming it is not a fabrication
do we have a reference, and if not let’s discuss the bio-electrical fields of rat hordes and how they affect the general emotional stability of population centers like New York
So when you read the scale, how many cars were in the parking lot?
there were 25 cars, but they didn’t count because they were full of flying birds
Exactly, but it would still seem to be supported by the earth eventually. (Steve-o’s reference is helpful, however.)
At any rate, consider the total weight of all planes, and all other vehicles for that matter. Could they even begin to equal a trillionth of the mass of the earth? Could they possibly account for the trillions of tons of missing weight?
Drum God suggested (in all seriousness, I’m sure) that we take the weight of all humans into account. Obviously, whatever weight we and other living things (yes, including cockroaches) have is derived from the earth itself and wouldn’t add to its weight, n’est-ce pas [note my clever inclusion of a foreign phrase in order to make myself sound more credible]? ;-{)}
Of course air has weight. That fact is so obvious when you think about it.
Hint: Think about the most-commonly used non-metric unit for measuring air pressure and think a little about how that unit was derived…
For the scientifically challenged, air pressure is commonly measured in pounds per square inch. Normal atmospheric pressure is roughly (very roughly) 15 psi. Ergo, a column of our atmosphere one square inch in area (about the size of a half dollar), reaching from sea level up beyond the most rarified heights of the stratosphere, weighs in at, you guessed it, roughly 15 pounds (+/- 1lb; I really don’t feel like looking it up. I can’t remember SP in psi anymore since all I use these days is bar(1), inHg(29.92), or mmHg(760) to measure pressure.)
[hijack]
David Barry wrote this in an article on 5/28/1989:
Unfortunately, I would need to pay the San Jose Mercury News a couple of bucks to get the full article.
If memory serves, after describing the setup used to alert Nixon when he should laugh, he describes a first group who think that it is funny. He then describes a second group who doesn’t think its funny to poke fun at someone so humorless as Richard Nixon. He says neither group are humor impaired. Its a third group of people, those who want to know how, exactly, the electrodes were set up to not cause serious damage, that are the humor impaired. People who just doen’t get the joke.
I don’t bring this up to imply that anyone on this thread may be humor impaired. Nope. That’s definitely not why I bring this up.
[/hijack]
Son Tinh & JackPunch:
I see some confusion here:
Centripetal force is that force which pulls an orbiting object towards the center about which it orbits. [Latin centrum center + petere to seek]
Centrifugal force is that force which pulls an orbiting object away from the center about which it orbits. [Latin centrum center + fugere to flee]
The orbits of the planets (the explanation goes) are maintained by a balance of centrifugal and centripetal forces.
However, it should be noted that according to modern physics (since Newton), that kind of centrifugal “force” is not a force, but an effect of inertia (an object in motion tends to maintain that motion). Further, “centripetal” refers to the direction of a force, not its origin or nature. Physics since Newton has considered the centripetal force that governs planetary motion to be “gravity” (a mysterious term, apparently meaning “inexplicable but measurable centripetal force”).
Thus, the centripetal force is gravity. It’s not generated by motion, but by mass. “Centrifugal force” on the Earth’s crust is a side effect of rotation–and would, I guess, account for some lessening of the Earth’s “weight.”
*At least, that’s what they want you to think./i]
You know what’s really humiliating? I was bragging about how I had made it into two threadspottings in a row, and commented that someone needed to nominate a physics thread so I could make it three. Well, not only does it turn out to be a physics thread, it’s a General Relativity thread, and for some odd reason, I hadn’t posted to it. Argh.
And btw, I’m (almost) certain that Achernar was joking about air having no weight-- He knows better than that (and if he doesn’t, there’s some professors I’m going to have to e-mail).
[QUOTE]
**
Aren’t we measuring the weight of the planet with all it’s stuff on it? People must add significantly to the weight. Then there’s the other animals. The buildings, the cars, the boats, the airplanes (not flying). Why even all the cockroaches in the world must add some weight. I’ve seen some around here that weight at least half a pound.
SNIP
Actually if we take away all the humans and animals and stuff, we will be taking away part of the Earth itself. By your argument the earth gets heavier every time a baby is born. But simple conservation of mass tells us that while women may be quite clever in making babies, all they are doing is taking molecules that already existed billions of years ago and rearranging them into a baby shaped object.
My understanding is that the earth’s mass was fixed when it was created, and all the people and buildings and such are just rearrangments of this mass. The only difference is that it has gotten a little heavier from all the meteorites and such that have crash landed, and maybe a little lighter from the bits of sattelite we throw into space.
So this keeps the bathroom scale test valid with all the people around. Just lie on your back, get a good grip on the Earth and raise your legs in the air. Then balance the scales on your feet. Thus you weigh the earth with you on it and it is easy to read the measurement
I have succesfully removed 1 cc of the earth’s volume (using a ruler and a kitchen knife) and have placed it on a calibrated electronic scale with draft cage.
Now I am waiting for the paperwork to go through so I can escape the earth’s gravity well (via the space shuttle) to accurately measure the mass of the aforementioned volume.
P.S. Should I discount the mass of the .5cm of earthworm contained in the sample?
P.P.S. Boy, those guys at NASA are slow… it’s been, like, five minutes since I emailed them… no wonder they haven’t figured out that the earth is flat(How else could the archangels go to the corner of the earth or all those sailors fall off?).