#copyright (c) Aaron Titus, 2004
#licensed under the gpl license

#http://linus.highpoint.edu/~atitus/mandi/vpython

from visual import *

print "Simulation of a Ferris Wheel"
print "----------------------------"
print ""
print "The yellow vector is the force of the chair on you. The blue vector is the gravitational force of the Earth on you. The green vector is the net force on you."
print ""
print "Change the period, T, to 5 seconds and you'll notice that you need a seatbelt at the top of the Ferris Wheel"
print ""
print "Change T to 10 seconds and you don't need a seatbelt at the top."

dtheta = 45./180.*pi #increment angle to draw ferris wheel bars
r=10. #radius of Ferris wheel
theta0=0. #starting angle
rodRadius=dtheta/10. #radius of wheel spokes
rodColor=color.yellow #color of wheel spokes
chairColor=color.magenta #color of chairs
fnetColor=color.green #color of net force vector
fChairColor=color.yellow #color of chair force (on you) vector
fGravColor=color.blue #color of grav force vector
chairW=r/10. #chair width
fScale=1./2.0e2 #scales force vector
vecShaftWidth=0.5 #shaftwidth for vectors

m=90. #mass of person

scene.autoscale=0
scene.range=1.2*r

phi=0. #angle of rotation
T=5.	# period of rotation
omega=2.*pi/T #initial angular speed
alpha=0. #angular acceleration

#lists
rods=[]
chairs=[]
fnetVectors=[]
fChairVectors=[]
fGravVectors=[]


#create objects
for theta in arange(theta0, 2.*pi, dtheta):
	chairPos=vector(r*cos(theta),r*sin(theta),0)
	chairs.append(box(length=chairW, width=chairW, height=chairW, pos=chairPos, color=chairColor))
	rods.append(cylinder(radius=rodRadius, pos=vector(0,0,0), axis=chairPos, color=rodColor))
	fnetVectors.append(arrow(pos=chairPos,axis=vector(0,0,0),color=fnetColor,shaftwidth=vecShaftWidth));
	fChairVectors.append(arrow(pos=chairPos,axis=vector(0,0,0),color=fChairColor,shaftwidth=vecShaftWidth))
	fGravVectors.append(arrow(pos=chairPos,axis=vector(0,0,0),color=fGravColor,shaftwidth=vecShaftWidth))

#time interval
#dt=T/1000.
dt=T/100.

while 1:
	rate(10)
	omega=omega+alpha*dt
	dphi=omega*dt
	s=omega*r
		
	for i in range(len(rods)):
		rod=rods[i]
		rod.axis=rotate(rod.axis,angle=dphi)
		chair=chairs[i]
		chair.pos=rotate(chair.pos,angle=dphi)
		if i==0:
			rVec=chair.pos
			rUnit=rVec/mag(rVec)
			fnet=m*s**2/r*(-rUnit)
			fnetVectors[i].axis=fnet*fScale
			fnetVectors[i].pos=rVec
			fGrav=m*vector(0,-10,0)
			fGravVectors[i].axis=fGrav*fScale
			fGravVectors[i].pos=rVec
			fChair=fnet-fGrav
			fChairVectors[i].axis=fChair*fScale
			fChairVectors[i].pos=rVec