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1813
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location San Mateo, CA
age 59
visits member for 3 years, 4 months
seen 6 hours ago

6h
comment What distance does one travels in his lifetime?
You might look at what-if.xkcd.com/86 where he compares the distance traveled by Voyager 2 (launched in 1977) to the distance traveled by a 1977 Plymouth Voyager and some other objects in various coordinate systems.
6h
answered equivalent spring constant for a nonlinear spring force
1d
comment It seems that the harmonic (integer multiple) overtones of a sound usually all have the same phase. Is this true, and if so why?
If you pluck a string at the center and do the Fourier analysis, all the harmonics are in phase. That is the expansion of a triangle wave.
1d
comment How would normal matter behave under conditions found in the core of the sun?
@AbanobEbrahim: Oops, you are right. I counted the $9$ twice. It is $10^{31}$ J That comes even more quickly.
1d
comment How would normal matter behave under conditions found in the core of the sun?
This page estimates the heat of vaporization of crust as $10 GJ/m^3$ From Wikipedia we find the heat of vaporization of iron to be about $11 GJ/m^3$ dominated by heating the material to boiling. With the volume of the earth $10^{21} m^3,$ we need $10^{40}$ J to vaporize it. That comes very quickly.
1d
comment Negative energy levels in the diagram for a hydrogen atom
This is the same as is done for gravitational potential. We say the potential between two motionless bodies infinitely far apart is zero. As they approach each other, the energy decreases, so the potential energy is negative.
1d
comment Ice and liquid water interacting across a boundary
There is no specification of gravity in the problem, so ice floating is not important. You are correct that entropy will increase if heat flows.
2d
comment Ice and liquid water interacting across a boundary
In classical physics, temperature differences are the only thing that drive heat flow, so in your model there is nothing to drive heat. You are correct that the entropy will rise if heat flows from the water to the ice. Over the long term quantum effects will force energy to tunnel and equalize the energy per mass content.
2d
revised Ice and liquid water interacting across a boundary
added 183 characters in body
2d
comment Ice and liquid water interacting across a boundary
Remove the barrier, we have a liquid/solid mix that is (if the pressure is right) at the equilibrium temperature. What makes heat flow? You are correct that if heat flows from the liquid to the solid the temperature of each will not change, compensated by freezing/melting.
2d
answered Ice and liquid water interacting across a boundary
2d
answered Gravity beneath sea level
Aug
28
answered How can metal objects become electrically charged, if current flow means that an equal number of electrons enter/leave the object?
Aug
24
revised How can Excel be used to model the flight of a rocket?
add info
Aug
24
comment The thermodynamics of heating water in a rigid container
The only ways you have to absorb heat are to increase the temperature of the system or to convert liquid to gas. Clearly increasing the temperature will increase the pressure of the gas. To increase the volume of liquid you have to have the thermal expansion of the liquid very high, the compressibility of the liquid low, and the heat of vaporization high. I admit I don't have a proof that there cannot be a liquid like this, but usually more will boil than the expansion.
Aug
24
answered How can Excel be used to model the flight of a rocket?
Aug
24
answered The thermodynamics of heating water in a rigid container
Aug
23
comment Quantum machanics powering by -2?
I'm sorry, but "we power by -2" doesn't mean anything. You need to be more specific in your question. Maybe the context would help (but I still can't understand the phrase).
Aug
21
awarded  Civic Duty
Aug
16
comment Does decreasing the length of the line between a harness and zip wire increase the velocity at which you travel?
If I had to guess, the long harnesses for customers go with trolleys that have more resistance in the wheels. It is not about the length of the line, but about making sure the customers don't arrive at the bottom with too much speed. The instructors have training and gloves so they can slow down when needed.