from visual import *
# David Scherer
dt = 0.1
g = []
for i in range(3):
g.append(display(x = 0, y = 30 + 200*i, width=600, height=170))
g[0].title="k=6N/m mass=2.0kg"
g[1].title="k=6N/m mass=1.0kg"
g[2].title="k=6N/m mass=0.5kg"
bands = [ curve( x = arange(-50,50), display=g[0], color=color.red, k = 6., mass = 2.0),
curve( x = arange(-50,50), display=g[1], color=color.yellow, k = 6., mass = 1.0),
curve( x = arange(-50,50), display=g[2], color=color.green, k = 6., mass = 0.5),
]
for band in bands:
band.radius = 0.5
band.momentum = zeros((100,3),float)
### Uncomment exactly one of the following lines: ###
band.momentum[:25,1] = sin(band.x[:25]*pi / 25.0)*3 # half-wave pulse
## band.momentum[:25,1] = sin(band.x[:25]*2*pi / 25.0)*5 # full-wave pulse
## band.momentum[:25,0] = sin(band.x[:25]*pi / 25.0)*5 # compression wave
## band.momentum[:,1] = sin(band.x * 4 * pi / 100.0)*2 # standing wave
## band.momentum[25,1] = 20 # single point impulse (messy)
while True:
rate(100)
for band in bands:
# Keep endpoints fixed:
band.momentum[0] = band.momentum[-1] = vector(0,0,0)
# Integrate velocity:
band.pos = band.pos + (band.momentum/band.mass*dt)
# force[n] is the force on point n from point n+1 (to the right):
force = band.k * (band.pos[1:] - band.pos[:-1])
# all points but the last experience forces to the right:
band.momentum[:-1] = band.momentum[:-1] + force * dt
# all points but the first experience forces to the left:
band.momentum[1:] = band.momentum[1:] - force * dt
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