G is just a number. It stands for 6.67384 × 10-11 m3 kg-1 s-2 and is therefore always positive. The masses, m1 and m2, are also always positive, and R^2 must be positive because it is the square of a real number. Therefore, in order for the force to be negative, which it needs to be to point...
There is no rule that says that negative force is attractive. The minus sign does not mean that gravity is attractive. It means that gravity is pointing in the negative r direction. This is what you want since you are using spherical coordinates with r=0 is defined as the centre of the star, and...
Just one thing to be careful about. Do not forget about the sign of the force. Your gravity equation has a minus in it, which means the force is negative. Since gravity points towards the middle of the star, that means that positive force is by definition away from the centre of the star...
F(press)=(P(r+dr))- P(r))dA)
Remember that force is pressure multiplied by area. This appears to be saying that the net force on the cylinder is the force on the top of the cylinder pushing downwards minus the force on the bottom of the cylinder pushing up.
I have just had a short discussion with somebody online about how some scientific terms are hugely misleading due to some historical misunderstanding. The example that I put forward was the term 'planetary nebula', which was originally given to objects that looked like planets in poor quality...
I am currently doing a bit of research into the history of our understanding of the solar magnetic field. It is quite interesting.
As I understand it, sunspots, which were observed at least as early as the time of Aristotle, were the first solar magnetic phenomenon to be observed. Can...
This is an interesting discussion and I have nothing to add but a question. So what you are saying edwinhubble is that gravitational waves carry a lot of energy, but do not dissipate that energy very well? Does this result come directly from theory (i.e. GR) or is it set by the inability of...
Hi Mun
I am not sure that there actually is a particularly rigidly defined set of definitions for these terms and I find that they are often used to mean different things. In my experience, 'orbital velocity' and 'rotational velocity' generally mean the same thing when you are discussing an...
I will take the two questions in reverse order. "If you were moving a long with speed, whilst someone else was stationary would you not measure light to be slower?? "
No.
"How can time be relative and speed of light absolute?"
Do you have any reason to think that the speed of light is relative...
This was answered on a previous thread. I have not read all of this one so it may have already been answered here, but this is what I said the last time.
Suppose there is an inertial frame, F, such that event A precedes event B and the two have a time separation in F of dt and a spatial...
In general rel, there may not be such a thing as a straight line in a spacetime with a funny geometry. When not under the action of external forces, things travel along geodesics. In flat "minkowski" spacetime, this principle corresponds to straight lines and is simply a more general form of the...
Just to elaborate on the two great answers given by Rasalhague slightly. Rasalhague stated that the fact that given a frame where an event A precedes an event B, it is only possible to find a different inertial frame where B precedes A if the faster than light transmission of information is...