Talk:Space Transport and Engineering Methods/Physics

Text on this page was copied from Rocket Propulsion/Temporary on September 6, 2006. Please see that page for the edit history before that date. Thenub314 (talk) 10:11, 13 August 2009 (UTC)

Just gave this lecture and wanted to know what students may find on web.

Error in enthalpy formulas here:

Specific energy is cVT

Specific enthalpy is cpT

Units System
Regarding "Weight is in reference to the local gravity field, while mass is the more correct unit to use at any location."

So what is the standard for mass ? Does mass equals weight on earth's locality. If so how is it precise, since it weight is not standard across the globe (as described).

If I remember correctly units of measurement are equal (for weight and mass) but it is also true to very small amounts lets say atomic size ? Taking a look into mass is extremely confusing due to all large number of information it provides bit couldn't find a direct answer to these questions. That should be interesting to add to the text.

A more esoteric question, can mass be considered a dimension (not only a characteristic or measurement). Since mass is independent of time (and even location, since it is postulated to be an effect induced external influence), this is intrinsically related to gravity (that is still not fully understood, and mostly hypothetically explained). --Panic (discuss • contribs) 16:41, 22 June 2012 (UTC)


 * The SI unit of mass is the kilogram, and the unit of force is the Newton (kg-m/s2). Pounds are a force unit. So, no the units are different.  Colloquial usage is to call your weight on Earth as so many kilograms, but that is incorrect for engineering or science. Your weight would be much less on the Moon (either in Newtons or pounds), because the Moon would be accelerating you less.  But your mass remains the same in either case.  The standard for mass is a reference kilogram made of platinum-iridium and kept in a vault in France, and 40 copies thereof distributed around the world. There are efforts to redefine the kilogram as a specific number of atoms of carbon or silicon, because with modern instruments you could count them directly, and not depend on a human artifact for the definition.  Instead it would be based on natural atomic properties. Those efforts are not complete, so for now, a kg is based on a reference kg physical object.


 * Mass is considered in physics to be a property caused by the Higgs field (of which the soon to be discovered Higgs particle is the carrier), or the interaction of particles with the surrounding quantum foam of virtual particles. The effect is a resistance to acceleration, which is how we measure it. Einstein equated mass to energy by his famous equation, so the way to think of it is not as a dimension, but direction.  Matter is energy moving purely in the time dimension of a 4 dimensional space-time, while photons are energy moving at a 45 degree angle to the time dimension (they move as much in space as in time). I'm not sure how any of this affects the text of the book. Danielravennest (discuss • contribs) 19:14, 22 June 2012 (UTC)


 * As a reader, I'm operating in that function as a reviewer I think some of it are indeed interesting to add. I would add them myself but since you do not agree I will give you discretion on what to include.
 * The points that I find interesting and that I believe would complement the information on that section:
 * The clarification you provide regarding SI unit of mass and the units of force. Expanding a bit on the Newton on the text would be beneficial also as it is only mentioned as part of the energy formula.
 * Add how the SI is established and including the proposal for change would be interesting also.
 * Link it to the Higgs field theory (I note you optimism here)
 * A clarification about pounds (that unit is not used in my location, but I appreciated you exposition and I understood it, that may also be interesting to other readers)
 * It would also be an interesting location to mention density.
 * I've looked Kilogram Stability (and how mass is measured and established as SI unit, since gravity fluctuates). I'm still not happy with my personal understanding (or comfortable by the idea I get that this important measures are indeed imprecise).
 * For my edification alone can you explain me how they remove the gravitic dependency (that is even time changing, since Earths mass also mutates in general, as mater is collected and lost into space) influence of gravity ?
 * (I've read the section on the Proposed future definitions and understand that even gravity is very imprecisely measured and would only accounts to local gravity influence). I'm not a Physicist (or Material Engineer) my field is Computer Engineering but I've had always a curiosity about this subject since measuring instrumentation are the source of all science. --Panic (discuss • contribs) 13:13, 23 June 2012 (UTC)


 * I added more description about units system, and a link to the official pamphlet that defines the SI units. A link to the work being done to recast the SI units in terms of natural constants would be good. I have it on my task list to add more references throughout the book, and simply have not gotten to that yet.


 * Thanks that was the primary idea here. I will also attempt to help out where I can. --Panic (discuss • contribs) 00:10, 24 June 2012 (UTC)

Other things that should be covered
Vacuum and its characteristics. Radiation and the different units of measurement. --Panic (discuss • contribs) 23:18, 31 August 2012 (UTC)


 * Vacuum per se does not have characteristics unless you mean at the quantum level. I assume you mean the space environment - radiation, temperature, meteoroid flux.  I planned to cover that under Space_Transport_and_Engineering_Methods/Design_Factors - Operating environment, but had not gotten to that yet.  Note that surface environments, such as for the Moon and Mars, would be different than open space. Danielravennest (discuss • contribs) 09:51, 1 September 2012 (UTC)


 * Yes they have atmosphere, the moon gaseous ejections are still weird and strangely less studied (I have seen somewere a list of observed phenomena, that at times seems to emit light at the source) http://www.sciencedirect.com/science/article/pii/0019103567900449 http://www.sciencemag.org/content/155/3761/449.short  --Panic (discuss • contribs) 11:10, 1 September 2012 (UTC)