gravity.. a question from a bus driver:-)

Vorde

I don't have anything to substantiate myself on this, but that seems very unlikely. First of all the percent uranium in the earth is very, very small. Second of all I know how immense the pressure at the core is so I am very skeptical about it being anywhere close to even a fraction of the responsibility for the heating of the earth's core compared to pressure heating.

I'd love for someone to show me otherwise though.

D H

Quote by mesa

I thought the majority of the heat in the Earth was from radioactive decay of things like Uranium?

Yep. Nowadays, at least. Sources of the heat (better said: enthalpy; objects don't contain heat) inside the Earth are radioactive decay; residual heat (enthalpy) from the differentiation of the Earth into core, mantle, and crust; residual heat from the initial formation of the Earth; and continued tidal stresses from the Moon and the Sun. Depending on who you read, radioactive decay is currently responsible for somewhere between 45% to 90% of the thermal energy that is being lost by the Earth.

Vorde

Well I feel like an idiot, does pressure really do that little? Though I guess this belongs in the geology section.

mesa

Quote by Vorde

Well I feel like an idiot, does pressure really do that little? Though I guess this belongs in the geology section.

You should feel smarter, we just learned something new ;)
Thanks for the clarification D H!

Drakkith

Quote by bigalzz

that's what i'm questioning.. if you go down on an elivator to the center of the earth (ignoring the heat etc.) as you decent, the mass above you will increase.. the mass to either side of you would be cancelled by oposite forces.. eg i will have "x" gravitational force to my right and equal to my left etc, so i will be unaware of any lateral forces...but the forces benieth me and above me will be changing.. at some point the above forces and the below forces will cancel eachother.. the center.. as you move away from the center you will reach a point i call nomonaly the "event horison" this would be the "spherical" center of gravity.. the point to which all the mass of the earth (and stars and black hloles) attracted.. again, it is counter intuitive and i surely expect to be shot down.. but i'd like to understand.

At the exact center the NET FORCE of gravity does cancel out on all sides, resulting in no feeling of weight. If we hollowed the Earth's core out slightly and teleported you inside it, you would not fall anywhere. However, the rest of the Earth is not at the center and IS feeling a net force which is always inward. What's holding that material up against the pressure? You are. Until you are crushed by unimaginable force.

To elaborate a bit, consider a slice or section of the Earth about 1/3 of the way up from the core. This section has more of the Earth on the coreward side of it than on the outward side. In addition, the matter above it is also being pulled down, so it has the weight of all the matter above it as well. Overall everything is feeling a net force towards the center.

Lsos

Despite the gravity at the center being zero, the pressure is immense because all that ~4000 miles of rock on one side of the earth is not so much attracted to the center of the earth, but to the ~4000 miles of rock on the OTHER side of the earth. So yeah, in the very center all the forces might cancel out, much like the forces from two cars colliding head on can "cancel" each other out...but nevertheless you DO NOT want to be in the center of those two cars. Unless, of course, you are inside this magical shell that keeps getting mentioned.

mesa

Quote by Lsos

So yeah, in the very center all the forces might cancel out, much like the forces from two cars colliding head on can "cancel" each other out...but nevertheless you DO NOT want to be in the center of those two cars.

That cracked me up, good analogy

Drakkith

Quote by Lsos

Despite the gravity at the center being zero, the pressure is immense because all that ~4000 miles of rock on one side of the earth is not so much attracted to the center of the earth, but to the ~4000 miles of rock on the OTHER side of the earth.

To avoid confusion of some readers, I would just like to clarify that "Gravity Itself" doesn't cancel out, but the net force from it does, as all the mass is pulling all of you equally from all sides.

Similar Threads for: gravity.. a question from a bus driver:-)
Thread	Forum	Replies
question if a driver would be thrown from a vehicle?	General Physics	5
Pro-E driver question	Computing & Technology	3
LED Driver thermal transfer question	Atomic, Solid State, Comp. Physics	0
DVD-ROM Driver question	Computers	8
interesting question about car driver	Introductory Physics Homework	3

Vorde Recognitions: Gold Member	Well I feel like an idiot, does pressure really do that little? Though I guess this belongs in the geology section.