need math help
BlitzPlus Forums/BlitzPlus Programming/need math help
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| Ok, im sure this is easy but i didnt pay attention in math too much :) ok currently i have a ship flying around, inertia and all works fine. What im trying to add is a planet in the center that has a gravatational effect ont he ships. Can anyone help me out with the equations i need to use to find out how much in each direction i need to change the ships x/y? Hopefully that makes sense :) ill draw a picture if noone understands. |
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| OK first you have to work out the distance of the centre of the spaceship from the centre of the planet. Use pythagorus for this e.g. radius = squareroot(x*x + y*y). Then give the planet a Mass (M), make up a gravitational constant G, then the gravitational acceleration on the ship is (G*M)/(radius*radius). This assumes that the ship has no (or negligable) mass. Now you have the gravitational acceleration it must be applied to the x and y intertia of your ship. But NOT just added on, it must be added on proportially to x and y. I think you can use Pythagorus for this too. You need to work out the ratio of x and y to the radius and multiply the gravitational acceleration by the ratio (which will be less than or equal to 1) . You might even be able to use sin and cos somehow (check this forum for a recent post on intertia EDIT: http://www.blitzbasic.com/Community/posts.php?topic=45268 but you need to know the angle so not much good!), but I have to go shopping now (cop out). Good luck |
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| I assume you're doing something like this for inertia: x#=x#+vx# y#=y#+vy# x,y is ship positions, vx,vy is ship speed in x and y directions. Any force on the ship doesn't directly change it position, it changes its speed. For gravity, the force falls off as 1/(r^2) , where r is the distance between your ship and the planet centre. r_squared=(x-planet\x)^2 + (y-planet\y)^2 force#=constant/r_squared The force is pointing in a direction from the ship towards the centre of the planet. The force in x and y directions is: fx#=force*(planet\x-x)/r fy#=force*(planet\y-y)/r (r=sqrt(r_squared)) I THINK that lot's right - you'll have to try it - may have some wrong. You'll get problems if r goes to zero - so keep your ship away from the centre of the planet or put a case in that skips the force if r is zero or v small. You could try a force of 1/r oor 1/sqrt(r) - not technically correct but whatever gives the game the best feel. You will have to play with the size of 'constant' aswell. |
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| ok i think i can go from there, well see :) thanks |
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