Text 19463, 68 rader
Skriven 2014-11-19 23:49:22 av Kees van Eeten (2:280/5003.4)
  Kommentar till text 19459 av Michiel van der Vlist (2:280/5555)
Ärende: Mass, weight and heaviness
==================================
Hello Michiel!

19 Nov 14 22:29, you wrote to Ward Dossche:

 MvdV> No. It is not the gravity as such that creates weight, it is the
 MvdV> opposing force that balances gravity that is the source of weight.

 There is a mutual force that attracts two bodies. That force is dependent
 on the mass of those bodies and their distance. When an object cannot
 accelerate due to contact with a surface, that force is balaced by a force
 in the oppsite direction. That force is sensed as weight.

 MvdV> Usually this happens when one is standing on the surface of the body
 MvdV> generating the gravity,

 MvdV> But, when on is not standing on the surface, but in free fall in vacuum
 MvdV> above the surface, there is no opposing force and hence no weight.

 Vacuum has noting to do with it. It only removes the resistence when you move
 through a medium.

 WD>>  The astronauts in the ISS do not experience weightlessness ... they
 WD>> are in a continuous fall.

 MvdV> So there is no force opposing earth gravity, they are indeed in free
 MvdV> fall and so zero weight.

 Yes there is an opposing force, they move very fast perpendicular to
 gravity. This causes a centripetal force that causes them to circle
 around the object pulling them. If they move faster the centripetal force
 will increase and they wil move away from earth. When they slow down they
 will move into the direction of earth

 WD>> So nowhere in our solar system is there weighlessness, right?

 MvdV> There is weightlessness everywhere, except when subject to an opposing
 MvdV> force, like when standing on the surface of a planet or other large
 MvdV> body...

 MvdV> Or.... when standing on a surface that is accelerating in een upward
 MvdV> direction.

 MvdV> Einstein's principle of equivalence says that an observer in a closed
 MvdV> room experiencing weight can not tell if the room is resting on the
 MvdV> surface of a planet or if it is in a space ship that is accelerating.

 MvdV> Inertial mass and heavy mass are one and the same. This theory has not
 MvdV> been falsified yet.

 WD>> And outside? I suppose the Sun also flies a path determined by some
 WD>> sort of gravity somewhere ... right? No?

 MvdV> The sun orbits the centre of the Galaxy. It takes about 200,000 years to
 MvdV> make a full round. (IIRC)

 MvdV> The galaxies are also subject to gravity. on a larger scale the
 MvdV> situation is more complex, than planets orbiting a star, but gravity is
 MvdV> everywhere.

 MvdV> But without a force opposing it, there is no weight.

 Agreed.


Kees

--- FPD v2.9.040207  GoldED+/LNX 1.1.5
 * Origin: As for me, all I know is that, I know nothing. (2:280/5003.4)