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: The density of space "air" around it... or lack of air has no effect other than producing drag. The density of the air does mathematically cause some bouncy but this is so insignificant as to not reasonably be noticed or measured - it certainly would not effect the rise of the bullet. So, centripetal force is the only force acting on it.

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QUESTION: Not "air".  Rather SPACE itself.  More precisely, the quantum Mass/Volume of Space.

1) The first statement is an incorrect assumption (false). Falling body's will fall at 32ft/sec above the earth regardless of their "weight", mass, or density. If a hammer and a piece of Styrofoam are released at the exact same speed and moment from an astronauts hand, they will continue to orbit side by side at the same altitude. If a second hammer is strapped to the first hammer, there will be no change in altitude. The only way to cause the hammer or foam to descend is to reduce it's speed. It does not matter what their "weight", mass, or density is - only speed determines their altitude.

2) The second statement is true if we assume a perfect vacuum. As stated before a slower speed will cause a lower altitude and raising the speed will cause the object to rise to a higher orbit altitude - it's weight, mass, and density have no effect on altitude, just speed.

3) The third statement is false. Centripetal force ONLY APPLY TO OBJECTS IN CIRCULAR MOTION TIED OR ATTACHED TO ANOTHER OBJECT WITH A DIFFERENT SPEED (this cause a change in angular momentum and is called centripetal force). If an object is unattached (free floating) there is no centripetal force. Think of centripetal force as the force on an a "string" or cable". A yo-yo with momentum has centripetal force with a string anchored, but if the string breaks there is no centripetal force on the yo-yo.  


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J. Zumwalt


Aeronautical Engineer, Pilot & Air-frame & Power-plant mechanic (A&P), Current president of EAA (experimental Aircraft Association) chapter 837 (Payette, ID), Past instructor, computers, robotics and aviation, Past Director of Maintenance (two airlines), Past Continental Airlines shift supervisor (Anchorage, Alaska)


FAA certified commercial pilot FAA certified (A&P) Air-frame & Power-plant mechanic Aeronautical Engineer - University of Anchorage (Alaska) High school instructor, computers, robotics and aviation Current president of EAA chapter 837 (Payette, ID) Past Director of Maintenance (two airlines) Past Continental Airlines maintenance shift supervisor (Anchorage, Alaska)

Current president of EAA chapter 837 (Payette, ID)

FAA certified commercial pilot FAA certified (A&P) Airframe & Powerplant mechanic Aeronautical Engineer - University of Anchorage (Alaska) FCC MROP-Marine Radio Operators License FCC GROL-General Radio Operators License FCC RADAR endorsement GEN FAM certificates MD aircraft GEN FAM certificates Boeing aircraft State Instructor License High school instructor, computers, robotics and aviation

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