Hi all,

This might seem a silly question to you all, but what exactly determines the mass of an object, specifically the earth?

Does the earth's mass include ALL its contents, i.e. does a new born baby contribute to the earth's overall mass? What about plants, cars, buildings etc. Are they all included?

Since the mass is usually calculated using gravity, it would include all of the objects on the surface too. However, I am sure that all the objects on the surface are such a small fraction of the total mass that they are pretty much negligible.

Well, is 7 Billion people a small fraction? What exactly is the earth's weigth?

Well, is 7 Billion people a small fraction? What exactly is the earth's weigth?

 

Its mass is about 5.9742×10²⁴ kg

 

Lets say each person has a mass of 75kg, 5 billion is 5×10⁹ This is a total mass of 3.75×10¹¹

 

Which is a tiny fraction.

If you add the rest of the earth's material, i.e. cars, buildings and so forth, will this not amount to quite a bit?

Since all the matereials we use to construct buldings, cars etc comes from the earth then they will not effect the mass after their production (up to [math]E = m c^{2}[/math])

 

I don't think we gain or lose much mass to the cosmos. I was thinking about astoroids, comets etc...

If you add the rest of the earth's material, i.e. cars, buildings and so forth, will this not amount to quite a bit?

From a human perspective it appears to be very much, but the Earth is HUGE.

 

Cars, buildings and so forth is made from a tiny bit of the crust and the crust with all its mountains and oceans are still just a very small part of Earth.

 

You may want to read this: http://en.wikipedia.org/wiki/Structure_of_the_Earth

Thanks guys.

One more thing. Whats the formula for calculating gravity?

Whats the formula for calculating gravity?

http://en.wikipedia.org/wiki/Gravity

One more thing. Whats the formula for calculating gravity?

[math]g=\frac{GM}{r^2}[/math]

g being the strenth of the gravity.

G G being the gravitational constant (a very small number).

M being the mass of the attracting body.

r being the distance from the centre of the attracting body.

A couple random things:

 

Even ignoring gravity, mass can be calculated via inertia, i.e. from the force needed to accelerate the mass a certain amount. Or, simply, mass is proportional to force divided by the resulting acceleration from that force. This (inertia), I think, is more fundamental to mass than gravity, but since they always go hand in hand it usually doesn't matter in practical terms, especially with large objects like planets where gravity is always measurable.

 

The Earth's mass actually increases every year by a few hundred tons because of space dust and meteorites. However, this is an immeasurably small fraction of the Earth's total mass.

I don't think we gain or lose much mass to the cosmos. I was thinking about astoroids, comets etc...

 

The earth slowly gains mass at this point. I believe mostly from interstellar winds, but also from asteriods and commets (luckily this has decrease in the earths present history).

 

However at a period this gain was far more extreem. The original earth was believed to be less than 40% of its current mass and the rest formed from many collisions in a relatively short period.

 

http://en.wikipedia.org/wiki/History_of_earth

The Earth's mass actually increases every year by a few hundred tons because of space dust and meteorites. However' date=' this is an immeasurably small fraction of the Earth's total mass.[/quote']

 

The earth slowly gains mass at this point. I believe mostly from interstellar winds' date=' but also from asteriods and commets (luckily this has decrease in the earths present history).

[/quote']

 

Interesting. Got any sources for that statement? Is it calculated or measured (the latter would violate the "immeasurably small fraction" ...)?

I remember reading that somewhere. I think it was calculated based on the mass density of objects intersecting Earth's orbit, be it solar wind, loose dust, intersecting meteroids, etc. It couldn't actually be measured, I don't think. I'll try and find a source.

Interesting. Got any sources for that statement? Is it calculated or measured (the latter would violate the "immeasurably small fraction" ...)?

 

Semantics. I think the fraction is immeasurably small, from a gravitational standpoint, so you measure the mass directly. The numbers used have been perverted by some YECs into arguing that the moon dust layer should be much thicker if the earth is really 4+ billion years old, so I'm sure details of the measurements could be found at talk.origins.org