Well with classes over, I wanted to at least do something with the year of University Physics torture I have endured. Thus I present Java Simple Physics. It is just a quick physics example that uses the kinetic and potential relationship to have balls with different gravity constants drop then bounce with no loss of energy. It took a few hours to get right, mostly because I either did not know what I was doing, or was over complicating things. I hope to slowly improve on this concept till I have a VERY simple physics engine. Hey, it can only help to have a physics engine laying around, one day I might actually need one.
import javax.swing.*;
import java.awt.*;
public class Physics extends Thread
{
private int worldx = 200, worldy = 900, worldtime = 15;
private JFrame frame = new JFrame();
private Ball ball,ball1;
public Physics()
{
// Set up frame
frame.setSize(worldx,worldy);
frame.setVisible(true);
// Make new ball
ball = new Ball(400,450,9.8,worldx,worldy,worldtime);
ball1 = new Ball(400,450,3.8,worldx,worldy,worldtime);
}
public void run()
{
while(true)
{
try
{
// Cover old draw with fresh screen
frame.getGraphics().fillRect(0,0,worldx,worldy);
// Move and paint ball
ball.move();
ball.draw(frame.getGraphics());
ball1.move();
ball1.draw(frame.getGraphics());
Thread.sleep(worldtime);
}
catch(Exception e){System.out.print(e);}
}
}
public static void main(String args[])
{
Physics p = new Physics();
p.start();
}
}
class Ball
{
private double gravity = 9.8, t;
private double x,y,v,a,m,dx,dy,dv,k,u;
private int worldx,worldy,dir=-1,width = 90;
public Ball(int xin, int yin, double g, int wx,int wy, int time)
{
// Set Constants
worldx = wx; worldy = wy-width; t = time;
// Reduce gravity to fit with drawing refresh rate
gravity = g * .02;
// Center ba;; on x axis
x = worldx/2 + width/2;
// Set varables
y = yin;
v = 0;
a = 0;
m=.8;
// Preset u and k values based on varables
k = (m * gravity * (worldy - width)) - (m * gravity * y);
if(k < 0){ k = 0; }
u = m * gravity * y;
}
// Catch and reverse
public void move()
{
// Calculate u and k
k += u - (m * gravity * y);
u = m * gravity * y;
//Find dv based on k = .5mv^2
dv = ((2 * k) / m) - v;
// Catch and reverse on k or u < 0
if(k <= 0 && dir == 1)
{
dir = -1;
v = v*(-1);
a = a*(-1);
k = 1;
u = m * gravity * worldy-width/10;
dv = -1;
}
else if(u <= 0 & dir == -1)
{
dir = 1;
v = v*(-1);
a = a*(-1);
u = 0;
k = m * gravity * worldy-width/10;
dv = ((2 * k) / m);
}
// Finalise new movement
y += ((1+dv)*dir)/t;
// Print out values when needed
//System.out.println("x:"+x+" y:"+y+" u:"+u+" k:"+k+" - dv"+dv*dir);
}
public void draw(Graphics g)
{
// Draw to screen
g.setColor(Color.GREEN);
g.fillOval(worldx - (int)x, worldy - (int)y - width/3, width, width);
}
}
