How do we know the mass of the Earth?

Put it in water and weigh the amount displaced – EASY!

A gentleman who's name I forget accurately surveyed Schiehallion and worked out how much it weighed.Its a very regular shaped mountain so reasonably easy to survey. He then stood next to mountain and measured the tiny deflection in a pendulum caused by mountain's mass/gravity then did some maths

Pretty basic, but seemingly very successful

All to do with density and gravity I reckon. Gravity is directly proportionate mass – we know the circumference of the earth hence volume.

Do some calcs and hey presto you've got the mass.

(disclaimer: actual sequence may be longer and indeed use completely different variables than indicated 😉 )

There'll be an app for that

😀

not sure we do to any accuracy

that bloke who measured the mass of a mountain had a stab at it

Its a made up number on the basis that you will never actually be able to weigh it.

Get some bathroom scales, place them face down on ground. The earth is now sitting on the scales and being accurately weighed, trouble is you can't see the dial.

A very big set of scales.

About the same as 5 bricks of gold, it would appear.

here we go…

Newtons Law Of Gravity – Calculating the Mass of the Earth Newton Discovered that First you must know how far an object is from the center of a planet or a sun. Then you must calculate the rate of acceleration that that object is accelerating towards that planet or that sun you can calculate the mass of that planet or sun because only an object of that planet's or sun's mass can accelerate an object towards it at that rate at that distance. This procedure was actually used to calculate the mass of the earth and can be used to calculate the mass of any orbited body, such as the Moon.

Hats off to Photographers Direct for obtaining conclusive documentary evidence. The camera indeed doesn't lie (although it does add 10 lbs apparently)

doesn't newtons law of gravity assume a point source for gravity though?

Its not about weight, its about mass. Weight is determined by gravity on a mass.

Therefore the weight of the earth would need to be determined by somthing other than the gravitational force of the earth.

Does this mean the earth is weightless? ❓

Mr you can approximate the sun as a point due to its distance to the earth. Plus in mechanics, you always apply the forces at the center of mass which is a point.

Does this mean the earth is weightless?

Depends if you're on the Earth or the Moon, dunnet.

m = g r² / G

G = 6.67300 x 10^-11m³/(kg s²)
g = 9.8 m/s²
r = 6.378 x 10^6m

Therefore m = 5.9742 x 10^24 kilograms

Simples.

p.s. the earth isn't a point mass of course, but because it's roughly spherical it doesn't matter.

I was walking on Whitby beach yesterday picking up stones looking for fossils and jet and I remembered hearing many years ago that all the rocks and stuff we find on the surface of the planet (and think are pretty heavy) are less dense than the rest of the planet. I think the theory is that all the heavy stuff sinks and the light stuff rises to the top.

Its not about weight, its about mass. Weight is determined by gravity on a mass.

Therefore the weight of the earth would need to be determined by somthing other than the gravitational force of the earth.

Does this mean the earth is weightless?

having proved the earth weighs nothing, mrben went on to prove that black equals white and got ran over at the next zebra crossing.

(i would however agree, sadly ive done my Earthscience degree, so cant use that as a smart arse answer anymore 🙁 )

That is pretty much it, BigJohn, the tectonic plates of the crust essentially float on the mantle, which is semi-solid rocks (peridotite, mainly) at high temperatures and pressures, kind of like the crusty skin you get on custard, and down below that the cores are liquid, then solid nickel-iron.

So, how heavy is it then?
I know.
I even know what it's obliquity of the ecliptic is.
& It's albido.
& even it's orbital velocity.

5,974,200,000,000,000,000,000,000 Tonnes if I understand Glenh.

5,972,000,000,000,000,000,000 tons, apparently.

It was measured back in 2000 and found to be lighter than anticipated.

its heavy then.

BigJohn – Member

5,974,200,000,000,000,000,000,000

WhatWouldJesusRide – Member

5,972,000,000,000,000,000,000

so not much room for error then

So are we saying that its really heavy or very dense!

Is there a difference? 😯

I get it at 6600 000,000,000,000,000,000. Just weighed it.
Wer'e bombing along at 66,000 mph as well.

its heavy then.

I wouldn't like it on me foot, put it that way.

it's on your foot now*

*assuming your foot is on the floor

Weird that, cant feel a thing!

woody2000 – Member
There'll be an app for that

POSTED 5 HOURS AGO # REPORT-POST

thanks, pmsl laughing at that! 😆

I think that variation was down to the difference between tons and tonnes.

I find it amusing that you should ask the question on a forum where people have the greatest difficulty in accurately weighing a bicycle.