Ask A Scientist Physics Archive

name         Len W.
status       other
age          40s

Question -   If, in theory, an object (e.g., an iron ball) reaches the state of having a temperature 
of absolute zero, does that state alter the degree to which the object will accelerate due to the 
gravitational influence of another object, e.g., the earth?
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There is nothing "mystical" about absolute zero. Gravity operates on the mass of a body according to 
Newton's law the force, F =  GmM/R^2 where m and M are the masses of the objects R is the distance 
between them and G is the universal gravitational constant. The temperature of either object does not 
affect the mass, the distance, or the gravitational constant.
It is worth noting that for historical reasons, temperature is defined in such a way that the "hotter" 
the body the larger the number we assign to its temperature. That is completely arbitrary. It would 
not be any problem to define temperature so that the "hotter" the body THE SMALLER THE NUMBER we 
assign to its temperature. In that case "absolute zero" just becomes "infinitely cold". And of 
course it is not possible to attain "infinitely cold". Mother Nature in fact hints that a 
reciprocal definition might have been a wiser more "natural" choice because in thermodynamic 
equations very often, if not the majority of the time, "temperature" appears as (1/T). The most
essential place this occurs is in the second law. There the change in entropy is defined as dS= dq * 
 (1/T).
 
Vince Calder
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Nope.   Gravity seems to be the most inviolable force in the universe.  Mass makes it, and large 
velocity affects it a little.  Otherwise, scientists tend to think in terms of space itself being 
continually sucked into the hole.

Now, maybe that iron ball will spontaneously do a teleportation exchange with an exactly identical 
iron ball on the other side of the universe, but gravity will be just as satisfied either way... 
and the iron ball that's here will keep on falling. Maybe all the atoms will become 
quantum-mechanically locked together, and it will be able to bounce off another such ball 
without denting or ringing or loosing any energy, but it will still be falling.

Not an expert, just a thought-perspective,

Jim Swenson
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The temperature of an object does not affect its gravitational properties except insofar as its mass 
changes as the temperature changes.  You know, I am sure, the famous Einstein equation E = mc^2 = mcc.  As the ball cools, the atoms reduce their thermal motion, moving more slowly and so reducing their kinetic energy.  Since the energy E of the ball decreases, its mass m must also decrease.

This is a very small effect, however, since most of the energy in the object is in its rest mass.  The 
amount of thermal energy in a 1 kg iron ball at room temperature is about 60,000 J.  The amount of 
energy in its rest mass is about 90,000,000,000,000,000 J.  This enormous ratio is indicative of the 
relative power of a nuclear bomb and a chemical bomb.

So to a VERY good approximation, the answer to your question is that the temperature does not affect 
gravitational forces.

It is worth mentioning that even if the mass changed by a lot, the acceleration of the iron ball near 
the earth's surface would not change, as shown by Galileo at the leaning tower of Pisa.  This is 
because the gravitational mass of the ball is exactly proportional (as far as we know) to the inertial 
mass of the ball.

Best, Dick Plano...
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