qrasy

well, I think the limit can be seen as : (lim(x->0) sin(2x)/x)*(lim(x->0) cos(3x)/cos(5x))*(lim(x->0) sin(4x)/sin(6x)) 2*1*4/6 4/3 to see whether this is correct, try to substitute small x such as 0.001 in calculator and see if the result is close.

I think of some sort of magnetic potential... It has to do with agnetic dipole.. Yeah, it has some potential that can "give" energy but returning to initial condition may "take" energy (converted to potential).

Human can't grow forever, however the organs are able to produce hormones for growing? I believe that its because after human body have developed fully, the organ became worse and worse, and will die. Human consists of cell, perhaps there are a limited number of cell reproduction so that human can't live forever.. I wonder why cells should eventually die in relatively short time. But I know even a machine cannot work forever... It would be broken.

By the way the topic there is about centrifugal force on the body on earth due to the rotation of earth, not the centrifugal force on Earth due to the rotation of earth-sun frame (revolution of earth).

I think in average balances each other in the rotating frame of earth and sun, otherwise will the distance between Earth and Sun will not be constant over years. In every season we can feel the change of the distance between Earth and Sun, though its only minor change (small compared to average distance), so one time Gravitational force is larger, another time the Centrifugal is. Remember that Centrifugal "force" is only pseduForce/fictional force. Pseudoforce is caused by accelerated movement of the system (an example: you can feel some "force" when you are in a car when it starts to go or stops). The velocity of Earth is clearly not constant, as it turns its direction.

There is no absolute frame of view, so "relative to space/time" is not well-defined. Rest mass is defined as the mass measured when the thing is not moving (well, there is no absolute frame so we should choose a frame in which it rests), it never change with velocity. Apparent mass grows larger as the speed approaches s. Remember the velocity and apparent mass correspondence is not linear so having infinite apparent mass at v->c does not imply anything in v->0.

No, there's no hidrogen released when the rust forms. I think it should be oxygen, electron+oxygen+water->hydroxide ion.