Ben Shell asked:
One thing I have wondered is how much does earth weigh? How many pounds does earth way, and if we don't yet know, do you think it would ever be possible to guess accurately?
KEEP UP THE GREAT WORK!!!
Chris - The stated weight – mass, we should more accurately, of the Earth is about 6 x 1024 kilograms. In other words, if you turn that into tons, it’s 6 with 21 zeros after it, tons. So pretty heavy, but the big question is and this is where Dave can help me out, how do we actually know that something on the scale of the Earth that we can't physically put on a pair of scales, how do we know how much that weighs because Archimedes famously said, “If you give me a lever long enough and somewhere far enough away to stand, I could lift up the Earth” but how would we have calculated how much the earth actually weighs, Dave?
Dave - Well, the simple way of doing this is because anything with a mass affects everything around it due to gravity. If it’s something roughly spherically symmetrical, you can assume that all the mass is in the centre of the planet and it behaves as if it was all the mass is right in the centre, due to some neat bits of maths. Basically, what you have to do is - if you know how much gravitational force a kilogram of anything will apply to another kilogram of anything, and you know how much force a kilogram of substance is being attracted to the Earth and you know how big the Earth is, you can work out how much mass must be in the Earth. The second part of that is really easy. Working out how much force a kilogram produces is really difficult because it’s about 10-11 Newtons at a metre between 2 kilograms. It’s an incredibly tiny force and it wasn’t done until near the end of 19th century.
Chris - Henry Cavendish, wasn’t it?
Dave - Yup. Indeed and you can work it out, and then from that, you can work out how heavy the Earth is, and from that, how heavy everything else is in the universe really.
BenTheH33 asked the Naked Scientists: One thing I have wondered is how much does earth weigh? How many pounds does earth way, and if we don't yet know, do you think it would ever be possible to guess accurately? KEEP UP THE GREAT WORK!!! Ben What do you think? BenTheH33, Tue, 23rd Nov 2010
http://lmgtfy.com/?q=How+much+does+the+Earth+weigh%3F Pikaia, Tue, 23rd Nov 2010
The earth weighs 6.5 x 10^27 in tons. But this is nothing on astronomical terms. Even a spoonful of neutron star would weigh about the same as all the buildings on earth. QuantumClue, Tue, 23rd Nov 2010
david holthaus asked the Naked Scientists: how much does the earth weigh? What do you think? david holthaus, Tue, 23rd Nov 2010
Calculating the mass of the Earth is fairly straightforward, but weight is relevant only in relation to gravity, but perhaps it was mass you were thinking of, in which case it's something like 5.9737 × 10ˆ24kg. Bill S, Tue, 23rd Nov 2010
I found a site that relates to the mass of the earth...
The value quoted by QuantumClue is not correct the correct value is 5.9742 × 10^24 kilograms syhprum, Tue, 23rd Nov 2010
We are talking about mass rather that weight, yes?
Good answer, maffsolo, but,David, is that what you were looking for? Bill S, Tue, 23rd Nov 2010
Two identical questions merged - sorry if it's a bit muddled right now! BRValsler, Tue, 23rd Nov 2010
10^27 tonnes DOES NOT equal 10^24 kilogrammes. Your answer was 10^6 times too big imatfaal, Tue, 23rd Nov 2010
Oh I see. Well that's not good. QuantumClue, Tue, 23rd Nov 2010
Plug and chug convergence calculator
The weight of the earth is equal to zero because it is in free fall motion around the sun
For me, the weight of the earth is equal to mine. I can feel it right now...
(is the earth accelerating around the sun? so from your own Newtonian equation a=0 so F=0,)
Foolosophy - yes the earth is accelerating (it's in circular motion; it must be accelerating) a≠0 F≠0. I agree with the Arkangel - although I think it weighs as much as me rather than as much as him imatfaal, Wed, 1st Dec 2010
do you know why there is weightlessness on an orbiting satellite?
Foolosophy - perhaps if you spent a moment with a basics physics text or even on wikipedia; the recommended reading topic is vector quantities with reference to velocity and acceleration (magnitude and direction). You will soon learn that scalars such as speed are not same as vectors such as velocity. Both forms of reference will also have a section on circular motion - that will fill the most obvious gaps. imatfaal, Wed, 1st Dec 2010
For instance, usually in very elementary physics, weight is the force exerted on a mass. The acceleration ''g'' is not zero in space. So setting g=0 for W=Mg is not exactly correct. It is true we experience weightlessness, but there is some debate as to whether this is technically correct. QuantumClue, Wed, 1st Dec 2010
"imatfaal" wishes to discuss the centrifugal force of a body in circular motion
the centripetal force is a different thing again
But most importantly though, Imatfaal needs to acknowledge the fact that the weight of the earth is equal to zero Foolosophy, Thu, 2nd Dec 2010
What is the difference between mass and weight?
It would certainly be quite hard to find bathroom scales that were capable of weighing it. Boots maybe?
quote author=JP link=topic=35346.msg332910#msg332910 date=1291277129]
I'm not quite sure what happened there, but this is what I tried to post:
It's hard to argue against "that isn't true," so here's some sources:
JP beat me to it!
Here's the problem, which is expressed well by the NIST and ISO disagreement on standards. Both say the equation for weight is
They don't get it.
BTW, the term "weightless", as frequently applied to objects that are orbiting the Earth at a particular speed, may be slightly suspect.
Actually, NIST says
g = G * M / R^2
it is a question of definition... CPT ArkAngel, Fri, 3rd Dec 2010
I wonder what Geezer's weight would be if he was on one of the Voyager probes heading towards the Ort cloud?
Hmm, maybe I should have read it all before writing :)
Hmm :) To me that's mixing relative mass, or momentum with 'proper mass'. In fact I believe that what I wrote is the correct definition of 'proper mass, well, as far as I know. 'Proper mass' is assumed to always be the same, in all 'frames of reference', be it at the EV of a black hole, or on Earth. yor_on, Fri, 3rd Dec 2010
Sorry about the choice of words, I'm kind of tired. I should have used 'proper mass is a invariant intrinsic property in all frames of reference'. I'm getting sloppy here, dangerous with you Guys and Gals :) yor_on, Fri, 3rd Dec 2010
I use proper mass as the definition of matter, rest mass when we discuss particles. Nice equations :) yor_on, Fri, 3rd Dec 2010
A couple of questions, Fool...
I know one thing. when discussing 'mass' in physics it's important to agree on what the he* we are discussing :) People use the same synonyms for totally different properties at times it seems.
I gave a reply to this, but it never processed. QuantumClue, Fri, 3rd Dec 2010
Fool's definition of weight may be correct, but he'll also have to be consistent. That means for example, that every time he accelerates his mass and jumps a few millimeters in the air, he is weightless (strictly speaking he'd need to be in a vacuum of course, which, come to think of it, might not be such a bad idea.)
I think I can present a argument speaking for my interpretation of 'proper mass'. Imagine yourself inside that 'box' described above, being 'at rest' with one of the 'particles'. When being so you will subtract the 'added' 'mass' as all motion can be seen, or transformed, into heat, and also as 'energy'. Being 'at rest', unmoving relative the particle will allow you to see it in its 'original state' and that state is also what I would call its 'rest mass' or if you like 'invariant mass' and those definitions are the equivalence to a piece of matter being 'proper mass', invariant in all 'frames of reference'. yor_on, Fri, 3rd Dec 2010