Feather Terminal Velocity Comparison: Mars vs. Earth Atmospheric Conditions

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In comparing terminal velocity for a feather dropped on Mars versus Earth, the discussion highlights the impact of gravity and atmospheric conditions. Mars has one-third the gravity of Earth and a significantly thinner atmosphere, which is 100 times less dense. The terminal velocity is influenced by gravitational force and atmospheric viscosity, with the latter being affected by temperature and pressure. While it is noted that viscosity is generally independent of pressure, the extreme low pressure on Mars raises questions about its effect on viscosity in this context. Overall, the consensus leans towards Mars providing a lower terminal velocity for the feather due to its weaker gravity and atmospheric conditions.
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Firstly, this isn't my homework question. I was trying to answer another, broader question for a student, and it boiled down to this one. There's quite a subtle point here, I think, but I just can't grasp it.

Consider stable atmospheric conditions on Mars and Earth. A feather is dropped from a great height on both planents. Which planet gives the feather the higher terminal velocity?

Data given is:
- Mars gravity = (1/3)g
- Earth atmosphere: 1000mbar
- Mars atmosphere: 10mbar

So terminal velocity goes as square root of gravitational force and inverse square root of viscosity. I can't work out how the viscosity changes with temperature and pressure.

Gut feeling tells you that the weaker gravity (a third of Earth's) contributes to lowering the terminal velocity. However, doesn't the fact that the pressure is 100 times smaller contribute to the viscosity somehow?

I remember proving in kinetic theory that viscosity is independent of pressure (except for high pressures), but does that hold here? I can't help thinking temperature has something to do with it as well.

Any explanation/calculation of Terrestrial/Martian atmospheric viscosity would be most appreciated.
 
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AFAIK, Mars' atmo is more akin to vacuum than it is to a real atmo.
 
DaveC426913 said:
AFAIK, Mars' atmo is more akin to vacuum than it is to a real atmo.

That's what I thought, but I can't find any expression for how the viscosity changes at low pressure.
 
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