from visual import *


L=10.0
k=0.5
F=0.5
alpha=2.0/3.0


def force(angle,angvel,t):
    result=-sin(angle)-k*angvel+F*sin(alpha*t)
    return result
    
    
ball=sphere(angle=1.0,angvel=0.0,
            color=color.red)

dt=0.01
t=0

while (1) :
    rate(300)

    t=t+dt
# leapfrog alg.
    a1=force(ball.angle,ball.angvel,t)
    ball.angle=ball.angle+ball.angvel*dt+a1*0.5*dt*dt
    
        
    a2=force(ball.angle,ball.angvel,t)
    ball.angvel=ball.angvel+(a1+a2)*dt*0.5