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QUESTION: If a bullet traveling beside the ISS was to gradually increase in mass (while continuing at the exact same velocity) it would slowly descend towards the earth as it orbits.

Now it is 30 m above the earth traveling at the same velocity as the ISS.  If its mass now remained constant and its velocity begins to increase, it will slowly rise upwards towards space while continuing to orbit.

Can we say that it moves upward not only do to its centripetal force, but also due to an increased density of the space surrounding it ?


ANSWER: Hello,

A typical bullet has a standard mass of ~ 100 g (0.1 kg). This is roughly the same as about 45% of meteoritic debris. Hence, at the velocity you are proposing (same as ISS) it would behave like meteoritic debris and be burned up in the Earth's atmosphere on entering it-  before it could ever get as low as 30 m, even if its mass increassed (refer to the Chelyabinsk object which burned up in February last year over Russia).

Hence, there is no chance of it's "moving upward".

Hope this helps!

---------- FOLLOW-UP ----------

QUESTION: Hypothetically if there was no atmosphere around the earth.


ANSWER: Ok, but look, you've already "hypothetically" presumed an atmosphere (and bear in mind we are talking about *Earth* (i.e. How could an airless world have occupants that launched an ISS?), not Mercury or an unknoown planet 'X')  by referring to "increased density of the space surrounding it".

Which, unless I've missed your meaning, has to refer to atmosphere. I mean, from where else would this increased density come?

In any case, even with the extremely implausible conditions you suggest, it is impossible that the bullet would "rise up" because - after increasing its mass (again, as you suggest) the increased gravitational pull of Earth (F ~ GMm/r^2)  would have ensured an ultimately decayed orbit and impact. Not "rising up".

Hope this helps!

Addendum: At a height of 30 m from 'Earth' the velocity of the bullet would have had to increase to 3.66 x 10^6 m/s to sustain any orbit - far less move up- which is preposterous, given the ISS velocity is only 7.71 x 10^3 m/s.   It is all very well to propose "hypotheticals" but we must expect some touchstone in reality, physical laws. (I.e. where will the energy come from to countermand the force of Earth's gravitational attraction?)

---------- FOLLOW-UP ----------

QUESTION: Philip you're hilarious !

> How could an airless world have occupants that launched an ISS?

That's exactly why we use the word hypothetical.

> would have ensured an ultimately decayed orbit and impact.

No the velocity was kept constant and only enough mass was added to bring it close to the earth.

Because space is not empty but made of quantum particles of mass we believe the increased velocity would indeed cause a higher density thus pushing the bullet upwards.

No intent to be "hilarious" but clearly I must have been. :) But this is why I reject most hypothetical questions unless they at least assume a relative basis in reality (i.e. if you are writing or talking about a problem relative to *Earth*, then we assume Earth parameters ab initio.

Thus, in my frame of reference, "hypothetical" has limits. If you choose the Earth as planet you're examining in a given problem context, then it has the density, mass, temperature profile etc. and YES ...atmosphere of Earth.

Re: Space not being empty, sure ok, but "quantum particles of mass x" would not have had any effect on macroscopic mass, e.g. a bullet.  See, for example, David Bohm's treatment in his book Wholeness and the Implicate Order.  Bohm notes 1 cc of empty space has a mass-energy that surpasses that of the known matter universe, but it can't be used to move or affect a macroscopic material particle.

Also, if you'd have more carefully specified this at the outset, with your question, I could have tailored the response more accurately. But with no other info, I had to assume you were writing of macrcscopic density, i.e. for atmosphere.

Further note: Don't believe everything you read on assorted websites, especially from amateur physicists. It looks like dreck to me.  


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Philip A. Stahl


I specialize in stellar and solar astrophysics. Can answer questions pertaining to these areas, including: stellar structure and evolution, HR diagrams, binary systems, collapsars (black holes, neutron stars) stellar atmospheres and the spectroscopic analysis of stars as well as the magnetohydrodynamics of sunspots and solar flares. Sorry No homework problems done or research projects! I will provide hints on solutions. No nonsense questions accepted, i.e. pertaining to astrology, or 'UFOs' or overly speculative questions: 'traveling through or near black holes, worm holes, time travel etc. Absolutely NO questions based on the twaddle at this Canadian site: purporting to show a "new physics". Do not waste my time or yours by wasting bandwidith with reference to such bunkum.


Have constructed computerized stellar models; MHD research. Gave workshops in astrophysics (stellar spectroscopy, analysis) at Harry Bayley Observatory, Barbados. More than twenty years spent in solar physics research, including discovery of SID flares. Developed first ever consistent magnetic arcade model for solar flares incorporating energy dissipation and accumulation. Developed first ever loop-based solar flare model using double layers and incorporating cavity resonators. (Paper presented at Joint AGU/AAS Meeting in Baltimore, MD, May 1994)

American Astronomical Society (Solar physics and Dynamical astronomy divisions), American Geophysical Union, American Mathematical Society, Intertel.

Papers appearing in Solar Physics, Journal of the Royal Astronomical Society of Canada, Journal of the Barbados Astronomical Society, Meudon Solar Flare Proceedings (Meudon, France). Books: 'Fundamentals of Solar Physics', 'Selected Analyses in Solar Flare Plasma Dynamics', 'Physics Notes for Advanced Level', 'Astronomy & Astrophysics: Notes, Problems and Solutions', 'Modern Physics: Notes, Problems and Solutions'

B.A. degree in Astronomy; M.Phil. degree in Physics - specializing in solar physics.

Awards and Honors
Postgraduate research award- Barbados government; Studentship Award in Solar Physics - American Astronomical Society. Barbados Astronomical Society award for service (1977-91) as Journal editor.

Past/Present Clients
Caribbean Examinations Council (as advisor, examiner), Barbados Astronomical Society (as Journal Editor 1977-91), Trinidad & Tobago Astronomical Society (as consultant on courses, methods of instruction, and guest speaker).

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