Momentum VPython Lab

from visual import *
scene.y = 400 # move animation window down 400 pixels from top of screen
from visual.graph import *
cart = box(pos=vector(0,-.05, 0), size=(1.5, 0.05, 1))
cart = box(pos=vector(-0.5,0,0), size=(0.1, 0.04, 0.06), color=color.blue)

cart.m = 0.80
cart.p = cart.m*vector(0.7, 0.2, 0)

deltat = 0.01
t = 0
mgraph = gcurve(color=color.green)

cart.trail = curve(color=color.red)

while t<3.0:
    rate(100)
    Fnet = vector(-0.4, 0, 0)
    cart.p = cart.p + Fnet*deltat
    print "t=",t,"cart.p=",cart.p
    cart.pos = cart.pos + (cart.p/cart.m)*deltat
    t = t + deltat
    mgraph.plot( pos=(t, cart.p.x) )
    cart.trail.append(pos=cart.pos)

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Analysis Questions

(1) Using the printed list of momentum vectors, calculate p v Δ . That is, pick one of the vectors to be the final

momentum, and subtract from it the vector just above it, which is the initial momentum:

Δp = p f − pi = ?,?,? kg m/s.

pi= <0.548, 0.16, 0>
pf= <0.544, 0.16, 0>
 (.544-.548, .16-.16, 0-0)
= <-0.004, 0, 0>
        

(2) Calculate the vector F Δt net v.

-0.4 (.01) = - 0.004 = J

(In the program, this would be Fnet*deltat.) net ?,?,? N s F Δt = ?,?,? Ns

(3) Do your calculations show that the change in momentum p v Δ is equal to F Δt net v.

Yes. The impulse is equal to the change in momentum.

(4) Look at the printed list of momentum vectors again. Why aren’t the y or z components of the momentum changing?

The momentum, in this simulation, is only changing in the x direction.