Question on dark matter

Question

Is there any simple calculation that help to proof the existance of dark matter??
I.e. M= (v square times r)/G

O...I know that, but have u got any calculation which help to explain the existance of dark matter???

Okay...So, can anyone very kindly tell me if there is anyway to work out the acceleration of the universe..Or any related calculation of dark matter???(Because one of the requirement of my project is to put down calculation related to the subject..)
Many thanks indeed

Answer 1

No. Untill now, no scientists can surely claim the existance of dark matter.
The term dark matter arise because when scientists observe the universe, they find out that the universe is increasingly expanding --the expand og the universe is accelerating. This violates the law of gravitation because gravity is always attractive, and even when the galaxies are very far away, they still act an attractive force to each other. Thus, the galaxies should be decelerating instead of accelerating. But that is not the case. So Einstein proposed that there is some dark matter in the universe which can account for the acceleration of the galaxies as dark matter will act a repulsive force on positive masses, ie it has negative mass and act as anti-gravity.
The concept of dark matter as a source of anti-gravity can also explain why gravity is so waek when compared to the other foundamental forces (strong, electromagnetic and weak force)
However, the dark matter (and the dark energy) is purely an hypothesis and is yet to confirm.

2007-03-25 10:07:49 補充：
If anyone can have a proof of the existence of dark matter, he/she will receive the nobel prize!

2007-03-25 10:08:50 補充：
Here are my suggestions of reference:http://en.wikipedia.org/wiki/Dark_energyhttp://en.wikipedia.org/wiki/Expanding_universehttp://en.wikipedia.org/wiki/Big_Banghttp://en.wikipedia.org/wiki/Dark_matterwikipedia is actually a very convenient source of reference.

2007-03-25 10:16:47 補充：
The calculation of the expansion of the universe is the Hubble's law:V=HDV=recessional velocity of the galaxy or other distant object D=distance to the objectH=Hubble's constant, measured to be (70 2.4/-3.2) km/s/Mpc by the WMAP probe

2007-03-25 10:18:20 補充：
I think the reference from wiki is already enough for a secondary level project.

Answer 2

Your equation is just a simple circular motion equation,

for an object with mass m revolving another object of mass M with radius r, then

mv^2/r is the necessary centripetal force which is provided by the gravitational force GMm/r^2, thus

mv^2/r = GMm/r^2

i.e. M = v^2.r/G