Talk:Ram pressure

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ram pressure not just supersonic[edit]

I challenge the assertion that "ram pressure" can only exist during supersonic flow. I would define "ram pressure" to be equivalent to the dynamic pressure of the flow, equal to (1/2) x (density) x (velocity)^2 in the incompressible regime, and defined by the total pressure/static pressure compressible relation in the compressible regime (Ma > 0.3). - Fyre4ce

Fyre4ce: you are absolutely correct and the article is misleading. It needs to be re-written totally. Luckily it is a short one! -- David W. Hogg 16:37, 3 January 2007 (UTC)
I am no expert on the concept of ram pressure but I challenge the suggestion that it is similar to dynamic pressure. I believe it is synonymous with stagnation pressure. Dynamic pressure is not a pressure in the usual sense - it is the difference between two pressures - stagnation pressure and static pressure. When a body moving with high Mach number experiences heating on its leading edges it is because of the high stagnation temperature associated with its Mach number. It is not because of the high dynamic pressure. Besides, US authors mostly define dynamic pressure as with the proviso that it is applicable only to incompressible flow. If we are talking about high Mach number flows we are talking about compressible flows. I am in favour of re-directing "Ram pressure" to stagnation pressure. Dolphin51 (talk) 04:59, 7 January 2008 (UTC)
This concept of ram pressure is rather vague to me, by reading the article (basically it's just pressure; what's so special about it?). Anyway, considering the usage of such expression in articles like Tunguska event and Meteoroid, I agree that it is more akin to stagnation pressure than dynamic pressure. Changing the merge template... any objections?
Giuliopp (talk) 00:42, 11 January 2008 (UTC)

ram pressure and buoyancy[edit]

Not a Physics student here. Just to add this: if any body can pressure any fluid, then the concept of ram pressure is strongly connected to the one of buoyancy, isn't it right? This should be mentioned and further explained in the main article, if my observation is correct. And, if it isn't, maybe it should be made clear as well.

No, this is not strongly related to buoyancy, because ram pressure does not require gravitational forces, while ram pressure requires only relative motion. -- David W. Hogg 16:37, 3 January 2007 (UTC)

ram pressure vs viscous drag[edit]

This article should mention and distinguish ram pressure from viscous drag. The example at the end with the hand in the fluid may be dominated by viscous drag, not ram pressure. -- David W. Hogg 16:37, 3 January 2007 (UTC)

Just replaced that example with a more correct example (wind on body). -- David W. Hogg 16:45, 3 January 2007 (UTC)

I agree with David. Infact, the article does not clarify at all the origin (thermal/molecular/other?) of the phenomenon. I couldn't relate to the idea at all. I am aware of the concepts of Skin-friction drag and Pressure-drag. Is ram pressure the latter one? It'd be great to have some expert edit this article describing clearly the origins of Ram pressure. -- Ankurtg 19:56, 30 November 2007 (UTC)

etymology[edit]

Naive readers might find a brief explanation of the term's origin to be helpful. (I.e. "pressure" is clear, but "ram" needs to be clarified.) -- Gary Marcus, 16:48, 3 January 2007 (UTC)

..I suppose this is related to the "ramming air" meaning (??) 37.176.248.236 (talk) 12:10, 10 July 2016 (UTC)

redirect?[edit]

Should this not be a redirect to dynamic pressure? If not, what's the distinction? --Reuben 20:46, 25 July 2007 (UTC)

No, these are different. dynamic pressure is derived from Bernoulli's principle and equation, and is a mathematical term with specific units. It is a generic term for lots of situations. Ram pressure is for things, uh, ramming. Look at the articles linking in for ram pressure, and you will see astronomy... look at dynamic pressure and it is plain physics linking to it. Visitors to dynamic pressure won't expect ram pressure at all. I like to saw logs! (talk) 07:19, 10 January 2008 (UTC)

Now that makes more sense with that last update. I might concur with the merge onto Stagnation pressure however this might only be a "just because" change. Wikipedia has a lot of those. I like to saw logs! (talk) 23:04, 11 January 2008 (UTC)

Ram pressure formula incorrect?[edit]

Per https://ned.ipac.caltech.edu/level5/Sept08/Schindler/Schindler2.html, I believe the formula is incorrect, namely the constant term should be 1 not 1/2. Dcunning11235 (talk) 00:23, 18 January 2017 (UTC)

This may be due to the source (Gunn & Gott 1972) using an "approximately equals" to 1, while the (Bernoulli?) pressure is derived with the "1/2" term. I may make sense to change this to "approximately equals", then, depending on the context, which here seems to mostly astrophysical. Dcunning11235 (talk) 00:45, 18 January 2017 (UTC)

Original proposal re: galactic stripping[edit]

In addition to the Grebel, Gallagher, Harbeck source, should include a reference (and a sentence or two) pointing to (Gunn & Gott 1972) as early (or original?) proposers of ram pressure stripping gas from galaxies in clusters. Dcunning11235 (talk) 01:18, 18 January 2017 (UTC)