Shock Wave Questions: Calculating Speed & Intensity

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Discussion Overview

The discussion revolves around calculating the speed and intensity of shock waves generated by objects moving at high velocities, particularly in Earth's atmosphere. Participants explore the factors influencing shock wave characteristics and the relevant formulas for estimation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the formulas needed to calculate the speed and intensity of a shock wave created by a 10 kg object moving at 1000 m/s.
  • Another participant suggests that mass is less critical than shape in determining shock wave characteristics and notes the absence of a general formula for exact calculations, mentioning the use of normal shock relations for estimates.
  • There is a question about whether the shock wave travels at the same speed as the object, specifically in the context of an object moving at Mach 3.
  • A participant reiterates the idea that the shock wave's speed matches that of the object, emphasizing that once the object passes, the shock wave transitions into a sound wave.
  • Another participant agrees with the previous point but adds that the strongest shock waves are typically located in front of the object, challenging the notion of referring to the shock wave as being "behind" the object.

Areas of Agreement / Disagreement

Participants express some agreement on the relationship between the speed of the object and the shock wave, but there is disagreement regarding the terminology and the location of the strongest shock waves. The discussion remains unresolved regarding the exact calculations and the influence of various factors.

Contextual Notes

Participants acknowledge that the shock strength may vary at different points along the wave and that the calculations depend on the shape of the object, which introduces additional complexity. There is also a lack of consensus on the terminology used to describe the shock wave's position relative to the object.

nicholas0211510
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How would one calculate the speed of a shock wave or intensity? For example, let's say something with a mass of 10 kg, with a velocity of 1000 m/s, travling in a straight line ,in Earth's atmosphere, at sea level . what formulas would one use to figure this out? Thanks in advanced
 
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Mass is not as important as shape. That said, there still isn't any general formula to calculate it exactly and the shock strength will almost definitely vary at different points along the wave. Still, you can get a "worst case" estimate by using the normal shock relations to get the strength. It's speed is just going to be the same as the body.
 
Ah, so the shock wave behind it will have a equal speed as the object that created it? So if somthing is moving at mach 3 , the shock wave will be mach 3?
 
nicholas0211510 said:
Ah, so the shock wave behind it will have a equal speed as the object that created it? So if somthing is moving at mach 3 , the shock wave will be mach 3?
As far as I know, the shock wave is only the region where the air is being made to move 'faster than sound'. Once the object has passed by, the shockwave becomes just a sound wave. The air cannot support any higher speed than that without the energy supplied by the passing object and that dissipates pretty soon.
 
nicholas0211510 said:
Ah, so the shock wave behind it will have a equal speed as the object that created it? So if somthing is moving at mach 3 , the shock wave will be mach 3?

Correct, at least near the aircraft.
 
I'd also like to point out that saying the shock wave "behind" the object is misleading. The strongest shock wave(s) will be in front of (or attached to the front of) the object. There may or may not be anything behind the object depending on the shape.
 
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