#Spring in vertical posiion released from rest

from visual import*
from visual.graph import*

#create some graphs
graph1 = gdisplay(x=0, y=0, width=600, height=550,
             title='Spring  Energy', xtitle='Time(s)', ytitle='V(J)', 
             xmax=15.0, xmin=0., ymax=200, ymin=0, 
             foreground=color.white, background=(0.3,0.3,0.3))

VPlot = gcurve(color=color.red)
EPlot = gcurve(color=color.yellow)

#control how the scene will appear
scene.range = 15
scene.autoscale=0 #turn off autoscaling and user roation of scene
scene.userspin=0

#define the basic start up parameters
Li = 10.
ball = sphere(radius = 2.0, pos = (0,Li,0), color = (1,0.5,0.3))
spring = helix(pos=(0,0,0), axis=(0,10,0), coils=6, thickness = 0.45,radius=1.5)
spring.length = Li
ball.mass = 5
ball.vy = 0
k = 25
g = -9.81
b = 0.0 #linear spring damping term
L_eq = (Li+ball.mass*g/k) #the loaded equilibrium position
equilibrium = arrow(pos=(5,L_eq,0), shaftwidth=0.1, axis = (-4,0,0))

#since we are only interested in 1 dimension just use magnitudes here
F_ball = 0 #this is the force that the spring exerts on the ball = 0 until contact

time = 0
ts = 0.005 #need a tiny time step to keep errors down

while time < 15.0:
    rate(100)
    if scene.mouse.clicked:
        s = (Li-ball.pos.y)#stretch or compression in spring
        F_ball = k*s-b*ball.vy#upward force of spring on ball
        spring.length = spring.length+ball.vy*ts
        ball.vy = ball.vy + (g + F_ball/ball.mass)*ts #change velocity of ball
        ball.pos.y = ball.pos.y + ball.vy*ts #change position of ball
        time = time + ts
        VPlot.plot(pos=(time,0.5*k*s*s))
        #EPlot.plot(pos=(time,-ball.mass*g*(ball.pos.y-L_eq)+98.1))