# Tag Info

14

You probably got voted down cause this can easily be google searched, but the simplest way to explain it is that a tide happens because the lunar tug on one side of the ocean is measurably more than on the other side of the ocean and as the earth rotates the tidal "bump" follows the moon so you get 2 high tides and 2 low tides a day. A tide is effectively ...

6

There will be spoilers if you keep reading Firstly, he is shown surviving inside black holes. From where did he got oxygen? Perhaps from oxygen bottles. But, in an intense gravitational pull, how he survives? He would have got torn apart! am I right? The popular press says the word black hole and it is a bit vague what they mean because there are some ...

4

Then, shouldn't this sphere be detectable via the way it lenses light coming from galaxies that lie behind it (relative to earth). Similarly, a mass of dark matter within our own galaxy, should be detectable via the way it lenses light from stars that lie behind it ( again relative to earth). Has anything like this ever been observed? Yes, it should do ...

3

Neutrinos are produced in the atmosphere all the time as a consequence of cosmic ray interactions, and they mostly then fly right through the planet. So there is no problem with a source. In fact the "flying right through" bit is one of the problems: even the full diameter of a planet simply doesn't intercept a large enough fraction of the beam to make ...

3

The stars in the galaxy don't really orbit the black hole in the center of the galaxy. They all orbit a common center of gravity. Obviously, a lot of the mass is in the black hole, and the center of gravity could very likely lie inside the black hole's event horizon, but it's not required. Look here for a cool animation of Pluto and Charon orbiting a center ...

2

Like most proposals, it is possible of course; in physics we must ultimately test proposals experimentally. In the meantime (i.e. in this case whilst waiting for experimental observation and study of dark matter here on Earth), one must resort to assessing plausibility in the light of what we already know. There are two ways your proposal, if true, could ...

2

If you and then moon were together the earth would pull you both. It would pull the moon harder but since the moon is more massive this would (in the absence of other forces) produce the same acceleration as you undergo. If you factor in the moon pulling the earth up to it then since you and the moon are together the earth is pulled up to both of you. If ...

2

There is no requirement for a central black hole in a dynamical sense. Many galaxies are not known to have one, or if they do, its mass is relatively small. The gravitational influence of the SMBH can be quite negligible at distances that are only a tiny fraction of the size of a Galaxy. What I mean by this is that say the BH at the centre of the Milky Way ...

1

If you have a spherical body of radius $R$ with mass $M$, the gravitational field at any point at a radial distance $r$ is given by: $$\phi=\frac{GM(r)}{r^2}$$ where $M(r)$ is the mass enclosed inside a spherical shell of radius $r$. This is the only mass that matters in this case. (because of the Shell Theorem: https://en.wikipedia.org/wiki/Shell_theorem) ...

1

Limitations of $g \propto \frac{1}{r^2}$: The relationship $g(r) = G \frac{M}{r^2} \rightarrow g \propto \frac{1}{r^2}$ (where $g$ is the acceleration due to gravity, $G$ is the universal gravitational constant, and $r$ is the distance between the massive object and the accelerating object) is just fine in Newtonian physics—it doesn't need to be fixed. ...

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