I'm working on an Android game and I need to bounce 2 circles of each other (like 2 pool balls bouncing off each other). The collision is an elastic collision, and I need to calculate only 1 circles (called a Particle in my code) new velocity after the collision (the other circle, called a Barrier in my code will remain stationary and will not move because of a collision).
I am using a formula that I found on Wikipedia (http://en.wikipedia.org/wiki/Elastic_collision), but my end result for the new velocity of the particle after the collision is exactly the same as the velocity before the collision?
This is def wrong but I cant see where I am going wrong. Can anyone spot where I am going wrong?
I have just used a Java program to simulate my velocities and locations for the 2 circles as I dont wanna try it in my main Android game at the moment for fear of "breaking something"
Here is what I have so far (like I mentioned, this is just a simulation in NetBeans for the moment and I will use a menthod in my Android game to keep things a bit tidier):
double randomNextDouble = (new Random()).nextDouble();
System.out.println("Random.nextDouble: " + randomNextDouble);
double mathPI = Math.PI * 2;
System.out.println("Math PI: " + mathPI);
// get a random direction for the Particle to move towards
double direction = (new Random()).nextDouble() * Math.PI * 2;
System.out.println("Direction: " + direction);
// Then set the Particle's velocity - Increase to make Particles move faster
int velocity = 10;
System.out.println("Velocity: " + velocity);
// Then calculate the xv and the yv
// Velocity value on the x and y axis
double xv = (velocity * Math.cos(direction));
double yv = (velocity * Math.sin(direction));
System.out.println("\nXV: " + xv + "\nYV: " + yv);
// Genareting a random number for the Particle and Barrier's positions on screen
double Xmin = 0;
double Xmax = 300;
double Ymin = 0;
double Ymax = 300;
double randomNumber1 = Xmin + (int)(Math.random() * ((Xmax - Xmin) + 1));
double randomNumber2 = Ymin + (int)(Math.random() * ((Ymax - Ymin) + 1));
double randomNumber3 = Xmin + (int)(Math.random() * ((Xmax - Xmin) + 1));
double randomNumber4 = Ymin + (int)(Math.random() * ((Ymax - Ymin) + 1));
// Setting the Particle and Barrier's radius
double particleRadius = 8;
double barrierRadius = 16;
// Setting up the Particle and Barrier's mass
double particleMass = 100;
double barrierMass = 200;
// Assigning a random number to the Particle to simulate its position on screen
double particleX = randomNumber1;
double particleY = randomNumber2;
System.out.println("\nParticle X: " + particleX + " Particle Y: " + particleY);
// Assigning a random number to the Barrier to simulate its position on screen
double barrierX = randomNumber3;
double barrierY = randomNumber4;
System.out.println("Barrier X: " + barrierX + " Barrier Y: " + barrierY);
double distanceXToBarrier = barrierX - particleX;
System.out.println("\nBarrier X - Particle X: " + distanceXToBarrier);
double distanceYToBarrier = barrierY - particleY;
System.out.println("Barrier Y - Particle Y: " + distanceYToBarrier);
// Get the distance between the Particle and the Barrier
// Used for collision detection
double distance = Math.sqrt((distanceXToBarrier * distanceXToBarrier) + (distanceYToBarrier * distanceYToBarrier));
System.out.println("\nDistance: " + distance);
// Check to see if the Particle and Barrier has collided
if (distance <= particleRadius + barrierRadius)
{
System.out.println("Distance is less than 2 Radii");
}
else
System.out.println("Distance is NOT less than 2 Radii");
// Velx = (v1.u) * u + (v1 - (v1.u) * u)
// Vely = (v1.u) * u + (v1 - (v1.u) * u)
// Where v1 = xv and yv respectively
// Break it into 2 equations
// (v1.u) * u AND
// (v1 - (v1.u) * u)
//
// u = normalised Vector
// To normalize you just devide the x, y, z coords by the length of the vector.
// This then gives you the Unit Vector.
//
//Normalize the vector
double particleXNormalized = particleX * (1.0 / distance);
double particleYNormalized = particleY * (1.0 / distance);
System.out.println("\nParticle X Normalised: " + particleXNormalized +
"\nParticle Y Normalised: " + particleYNormalized);
// Calculating the first part of the eqaution
// (v1.u)
double v1DotUForX = xv * particleXNormalized;
double v1DotUForY = yv * particleYNormalized;
System.out.println("\nv1.u for X: " + v1DotUForX +
"\nv1.u for Y: " + v1DotUForY);
// The first part of the equation
// (v1.u) * u
double part1X = v1DotUForX * particleXNormalized;
double part1Y = v1DotUForY * particleYNormalized;
System.out.println("\nPart 1 for X: " + part1X +
"\nPart 1 for Y: " + part1Y);
// The second part of the equation
// (v1 - (v1.u) * u)
double part2X = (xv - (v1DotUForX) * particleXNormalized);
double part2Y = (yv - (v1DotUForY) * particleYNormalized);
System.out.println("\nPart 2 for X: " + part2X +
"\nPart 2 for Y: " + part2Y);
// Solving for:
// (((mass 1 - mass2) / (mass1 + mass2) * (v1.u) * u + ((2mass2) / (mass1 + mass2) * ((v1.u) * u))) +
// (v1 - (v1.u) * u))
double newXV = ((((particleMass - barrierMass) / (particleMass + barrierMass)) * part1X) + (((2 * barrierMass) / (particleMass + barrierMass)) * part1X) + part2X);
double newYV = ((((particleMass - barrierMass) / (particleMass + barrierMass)) * part1Y) + (((2 * barrierMass) / (particleMass + barrierMass)) * part1Y) + part2Y);
System.out.println("\nNew XV: " + newXV + "\nNew YV: " + newYV);
