from visual import *

print """
Bruce Sherwood Fall 2000
Four parts of program to illustrate rotating vectors:
(1) A rotating position vector; for example, planet in circular orbit.
(2) Also display momentum vector.
(3) On right, display momentum vector with tail at center.
(4) On right, display just the momentum vector
Click anywhere to advance from one part to the next.
The intent is to help in seeing that the momentum in circular motion
is itself a rotating vector, so that its rate of change is omega*p.
"""

scene.x = scene.y = 0
scene.width=800
scene.height = 600
rsphere = 0.08
shaft = 0.06
omega = 0.5
dt = 0.01
R = 1.
dx = 1.0*R
f1 = frame(pos=(-dx,0,0))
planet = sphere(frame=f1, pos=(R,0,0), radius=rsphere, color=color.green)
rvector1 = arrow(frame=f1, pos=(0,0,0), axis=(planet.x,0,0),
                shaftwidth=shaft, color=color.red)
vvector1 = arrow(frame=f1, pos=rvector1.pos+rvector1.axis, axis=(0,omega*R,0),
                shaftwidth=shaft, color=color.cyan, visible=0)
f2 = frame(pos=(dx,0,0))
rvector2 = arrow(frame=f2, pos=(0,0,0), axis=(planet.x,0,0),
                shaftwidth=shaft, color=color.red, visible=0)
vvector2 = arrow(frame=f2, pos=(0,0,0), axis=(0,omega*R,0),
                shaftwidth=shaft, color=color.cyan, visible=0)
scene.range = 1.2*(R+dx)
show = 0 # don't show vvector or frame2 initially

while 1:
    if scene.mouse.clicked:
        scene.mouse.getclick()
        show = show+1
        if show == 1:
            vvector1.visible = 1
        elif show == 2:
            rvector2.visible = 1
            vvector2.visible = 1
        elif show == 3:
            rvector2.visible = 0
            vvector2.visible = 1
        else:
            show = 0
            vvector1.visible = 0
            rvector2.visible = 0
            vvector2.visible = 0
    rate(100)
    f1.rotate(axis=(0,0,1), angle=omega*dt)
    f2.rotate(axis=(0,0,1), angle=omega*dt)