Felix Baumgartner and the speed of sound

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Discussion Overview

The discussion revolves around Felix Baumgartner's jump from 128,000 feet and the implications of breaking the sound barrier in relation to the varying speed of sound at different altitudes. Participants explore the factors affecting the speed of sound, including air density and temperature, and how these relate to Baumgartner's achievement.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants suggest that Baumgartner may have an advantage in breaking the sound barrier due to the lower air density at high altitudes, which could imply a slower speed of sound.
  • Others argue that the determination of whether he broke the sound barrier was based on the speed of sound in normal atmospheric conditions, not the medium he was in during the jump.
  • A participant notes that the speed of sound was not thoroughly discussed in relation to how it varies with altitude, prompting the creation of this new thread.
  • There is uncertainty regarding whether adjustments were made for the medium Baumgartner was in, with some participants claiming that such adjustments were considered.
  • One participant asserts that the speed of sound is primarily dependent on temperature rather than density, stating that it decreases with altitude due to lower temperatures, not lower density.
  • Another participant clarifies that while the speed of sound is slower at high altitudes, the reduced air density decreases drag force, allowing Baumgartner's terminal velocity to be supersonic initially.

Areas of Agreement / Disagreement

Participants express differing views on whether the speed of sound was adjusted for the conditions of Baumgartner's jump. There is no consensus on the implications of air density and temperature on the speed of sound in this context.

Contextual Notes

Participants reference the speed of sound's dependence on temperature and density, but there are unresolved aspects regarding the specific conditions during Baumgartner's jump and how they were accounted for in determining his speed relative to the sound barrier.

Hope Lansing
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Doesn't Felix have an advantage when breaking the sound barrier since the air in which he is moving is less dense, therefore the speed of sound itself is considerably slower?

(Felix Baumgartner is the man who recently jumped from 128,000 feet in an attempt to become the first man to break the sound barrier without the aid of a vehicle)
 
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You may be factually correct (probably are) but it is irrelevant because (as I understand it) they did not actually consider whether he was breaking the sound barrier in the medium he was IN, they just looked to see was he going faster than the speed that is the sound barrier in normal air.

I see there is a whole 'nother thread on this:

https://www.physicsforums.com/showthread.php?t=643395&highlight=Felix+Baumgartner
 
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I saw this thread. The speed of sound was more of an after thought, and it wasn't discussed to the extent to how it varies with the medium in which it travels, so I decided to start a new thread. Thanks for the reply. I agree that the sound barrier by which he is measured is the sound barrier in normal atmospheric pressure. I just thought it was worth mentioning.
 
One of the statements in the other thread said the poster thought that they HAD adjusted for the medium he was in but I have no idea if that's true.
 
My mistake then. I must have overlooked that bit.
 
I am pretty sure they did take into account the medium he was in. The sound speed decreases with altitude because, for a thermally and calorically perfect gas, it varies with temperature. It was all a matter of hitting the local speed of sound before the air got dense enough that the drag became too high. From everything I have seen, he made it to roughly Mach 1.24 in the air he was in at the time.
 
This is a common misconception - the speed of sound is independent of density for an ideal gas. It's true that the speed of sound is slower at high altitude, but this is an effect due to temperature - the speed of sound (assuming the gas composition is constant, and it behaves as an ideal gas, both of which are very good assumptions for the atmosphere at that altitude) is only dependent on temperature. Specifically, it is proportional to the square root of temperature. Because it is colder at altitude, the speed of sound is slower.

That having been said, the low density did work to his advantage - not by lowering the speed of sound, but by decreasing the drag force he felt at a given velocity. Drag force is proportional to density, so the vastly less dense air at altitude decreased the drag force enough to allow his terminal velocity to be supersonic, at least at first.
 

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