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# taby

Member Since 10 Feb 2005
Offline Last Active May 04 2015 08:38 PM

### In Topic: Combining meshes

04 May 2015 - 08:39 PM

You might want to check out CGAL.

### In Topic: Am I crazy for wanting to switch from Ue4 to Unity?

27 April 2015 - 11:07 AM

You could always try exporting some of the functionality into a library file (ie. a DLL file on Windows). That way you only have to recompile things that change in the main project.

### In Topic: X3DB format

21 April 2015 - 06:44 AM

### In Topic: How to create a circular orbit and an angry bird space like orbit ?

19 April 2015 - 01:02 PM

That's true; I see now.

One other question I have is why does he add the masses together like that.

### In Topic: How to create a circular orbit and an angry bird space like orbit ?

18 April 2015 - 03:53 PM

What I don't get is why this works: float force = Mathf.Sqrt (G * ((mBody + mPlanet) / r));

Have you read up on the subject of dimensional analysis?

http://en.wikipedia.org/wiki/Dimensional_analysis#The_fundamental_physical_constants

http://www.efm.leeds.ac.uk/CIVE/CIVE1400/Section5/dimensional_analysis.htm

For instance, let's analyze the equation for circular orbit velocity v = sqrt(GM/r)

G has dimensions of Length^3 Mass^-1 Time^-2

M has dimensions of Mass^1

r has dimensions of Length^1

GM has dimensions of Length^3 Mass^-1 Time^-2 Mass^1

GM/r has dimensions of Length^3 Mass^-1 Time^-2 Mass^1 Length^-1 which simplifies to Length^2 Time^-2

v = sqrt(GM/r) has dimensions of Length^1 Time^-1 (ie. metres per second, which stands to reason).

The problem that I have with your equation force = sqrt(G * ((mBody + mPlanet) / r)) is that it has dimensions of Length^2 Time^-2, which is not the dimensions of force (which is Mass Length Time^-2) -- in other words, the equation force = Mathf.Sqrt (G * ((mBody + mPlanet) / r)); makes no physical sense. I invite you to double-check my work, in case I made an error during the analysis of your equation. Plus, the practice wouldn't kill you.

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