CODEWITHSUNDEEP
actionscript-3mathcollision
Can Poyrazoğlu
Can Poyrazoğlu

Reputation: 34840

How to preserve speed after collision in two dimensions

I know this is pretty obvious but I'm having some trouble with a simple calculation.

I have an object that has X and Y components for its speed. I am calculating its total speed simply by square root of squares of the X and Y components:

var totalSpeed:Number = Math.sqrt(b.currentSpeedY * b.currentSpeedY + b.currentSpeedX * b.currentSpeedX);

I also have a variable called divergence, which is guaranteed to be between -1 and 1. According to the divergence, I calculate my new X component of the speed after the collision, by multiplying divergence and total speed:

var sX:Number =  -totalSpeed * divergence;

Now, as I have the new X speed, and the total speed, I simply obtain my new Y speed by subtracting the square of my new X value from total speed, and taking its square root:

var sY:Number = -Math.sqrt(totalSpeed - (sX * sX));

Here is my problem: The total speed before and after the calculations don't match. I can confirm this by both printing the total speed (root of sum of squares) before and after the collision, and by simply looking at the speed of the objects visually. After collision, the speed of the object always tends to be slower.

I am obviously missing something very simple somewhere, but unfortunatelly couldn't find it anywhere. Where is the error that prevents total sums from matching?

Upvotes: 1

Views: 103

Answers (1)

Justin Peel
Justin Peel

Reputation: 47092

In the sY calculatin it should be

var sY:Number = -Math.sqrt(totalSpeed * totalSpeed - (sX * sX));

Upvotes: 2

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