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Bouncing Ball Expression

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Chris Petri
Bouncing Ball Expression
on Dec 4, 2013 at 11:37:34 pm

Hey guys,
If got a litte problem with the bouncing-ball expression by Dan Ebberts.
A Ball gets shot with a defined velocity(v) and a Launch angle (elev). When it hits the floor, it bounces several times before it reaches its end-position.
I want to define a floor which the ball uses for bouncing after it got shot. The floor has to sit lower than the start position. The Y-Value doesnt need to be linked to a seperate floor layer. It works for me if I can define the value in the expression.
I´m sure this issue can be fixed with a just a little extra code but I don`t get it.
Thanks in advance!

Here´s the expression:

elev = degreesToRadians(75); //launch angle
v = 1900; // velocity
e = .7; //elasticity
f = .5; // friction
g = 5000; //gravity
nMax = 9; // maximum number of bounces
tLaunch = 1; // Launch-time

vy = v*Math.sin(elev);
vx = v*Math.cos(elev);
if (time >= tLaunch){
t = time - tLaunch;
tCur = 0;
segDur = 2*vy/g;
tNext = segDur;
d = 0; // x distance traveled
nb = 0; // number of bounces
while (tNext < t && nb <= nMax){
d += vx*segDur;
vy *= e;
vx *= f;
segDur *= e;
tCur = tNext;
tNext += segDur;
nb++
}
if(nb <= nMax){
delta = t - tCur;
x = d + delta*vx;
y = delta*(vy - g*delta/2);
}else{
x = d;
y = 0;
}
value + [x,-y]
}else
value


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