Kepler's Thrid Law

[airkyd]

ok , i know T^2 = k*R^2, but wat is K .

 

cans some one explain k to me. its a real complicated one :/

[lxxvii24]

ok ' date=' i know T^2 = k*R^2, but wat is K .

 

cans some one explain k to me. its a real complicated one :/ [/color']

my only contributioon is that , kepler's third law established this T^2 = k*R^3, tthat is all.

[5614]

Indeed it is:

 

[math]T^2 = kR^3[/math]

 

Where:

T = sideral period,

R = semi-major axis &

k = constant.

 

I believe it's something like if you use sidereal period in years and astronomical units then k is 1, so it becomes just [math]T^2 = R^3[/math]

 

Or something like that anyway!

[airkyd]

so wat is the constant , i understand the equation but i dont understand the constant bit , wat is its units , wat does it measure. i know that the constant varies for different garvitational forces. but tahts all l,

[Douglas]

K is defined here

http://www.phy6.org/stargaze/Skepl3rd.htm

[5614]

A constant is a constant.

 

What that means is that it is always the same number (assuming you use the same units).

 

So for example we all know e=mc^2 right, now what if I said that e=m, well that's wrong because you need to multiply m by c^2. Now we all know that c^2 will never change, it is a constant. This is what a constant is.

 

So you could say that:

10 = k5

where k is a constant. Obviously in this case k is 2. In this example the fact that k is always the same value isn't very important as 10 and 5 are also always the same value.

 

But say you were drawing the graph y=kx, y and x change all the time, but k is constant. What you know about the equation y=kx is that it pases through the origin (0,0) and that the gradient is k.

 

A constant doesn't have a unit, it is just a number to make the equation work. e=m doesn't work because e would be c^2 times too small, e=mc^2 does work. No matter what value of mass or energy you use they're always related by the constant value c^2.

 

[edit] ahh, Douglas's link just gave me the right words... for T^2 = kR^3 it means that T^2 and R^3 are proportional. They are proportional to each other by a value of k.

 

So like T^2 = R^3 is false because you need to multiply the R^3 value by k first... k is always the same number, no matter value of T or R you put in.