3 ms·
How do you know that? Consider a pretty simple and obviously correct device: an electric engine with an internal rotating shaft + a solar panel to power it, f
by duckingtest 10y ago
How do you know that?
Consider a pretty simple and obviously correct device: an electric engine with an internal rotating shaft + a solar panel to power it, floating in space. The faster it rotates, the higher its acceleration in the gravitational field.
- witty_username 10y agoThe engine would spin, but it would have 0 velocity unless it sent out something as exhaust.
- duckingtest 10y agoThat's not how general relativity works. Spinning would increase its energy, hence increasing its gravitational pull, hence accelerating faster.
- witty_username 10y agoBut momentum conservation holds in GR. I don't know GR, but approximately the Earth would also accelerate faster.
- duckingtest 10y agoConservation of momentum only works because the gravitational field itself is supposed to have momentum. Similar to how momentum is conserved for an accelerating paddling boat only if you include the sea. Sea analogy is a good one I think, especially because the gravitational field interacts with itself, like water, contrary to electromagnetic fields. Conservation laws in general are a quirky thing in GR, see: http://people.bu.edu/gorelik/ES_GG_Conservation_Laws.pdf http://people.bu.edu/gorelik/ES_GG_Conservation_Laws.pdf or http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/ http://www.preposterousuniverse.com/blog/2010/02/22/energy-i... for a shorter read >but approximately the Earth would also accelerate faster. Well yes, Earth has a stronger gravitational pull because of rotation. On smaller distances rotation effects become even more interesting: https://en.wikipedia.org/wiki/Frame-dragging https://en.wikipedia.org/wiki/Frame-dragging