python - Slowing down a physics defying spring -

i doing tutorial physics class.

i made program should have cart on box moved spring , should slow down stop, however, when run it, appears spring accelerating cart (no matter things negate.)

i have heard might issue vpython rounding numbers resulting in acceleration, if true, can make numbers 1000 times larger , fix it?

thanks!

from visual import * visual.graph import *  length=1.0  track=box(pos=vector(0,-0.05,0),           size=(length, 0.05, 0.10),           material=materials.bricks,)  # creates track "length"meters in # x direction, 0.05m tall, , 1m deep start=-0.5*length+0.05  cart=box(pos=vector(start+0.01,0,0),          size=(0.1,0.05,0.1),          color=color.green) k=-4 #spring constant  sprl=(start-0.05)-0.1  #sets position of left end of spring spring=helix(pos=(sprl,0,0),              axis=((cart.x-0.05)-sprl,0,0),              radius=0.02,              color=color.yellow)  cart.m=0.70 #mass of cart cart.vel=vector(0,0,0) #initial velocity of cart cart.force = k*(cart.x)*vector(1,0,0)  #force of spring cart.accel=cart.force/cart.m #acceleration of cart taking account fan t=0 deltat=0.01 end=0.5*length-0.05 #defining end of track gdisplay(x=100,          y=500,          xtitle='time (sec)',          ytitle='x (cyan), px (red)')  xcurve = gcurve(color=color.cyan) pcurve= gcurve (color=color.red)  while cart.x<end+0.01 , (cart.x>(start-0.01)):     #we include -0.01 cart not fail upon start...     cart.pos = cart.pos + cart.vel*deltat+(0.5)*(cart.accel)*deltat**2     #x equals x naught plus v times delta t plus 1 half delta t squared     #note ** means "to power of"     xcurve.plot(pos=(t,cart.x))     pcurve.plot(pos=(t,cart.vel.x))     cart.vel=cart.vel+cart.accel*deltat     #new velocity old velocity plus acceleration times time     cart.force=k*(cart.x)*vector(1,0,0)     cart.accel=cart.force/cart.m     spring.axis=((cart.x-0.05)-sprl,0,0)         t=t+deltat     #increments time     rate(100)     #rate means no more 100 loops per second 

you don't have dissipative force in system (one leaks energy out of it). equation f = -kx conserves energy (this equation have circuitously encoded , represents force spring exerts on object). note equation there doesn't mean force negative, points in opposite direction of cart.pos. how sinusoidal motion.

a dissipative force needed object slow down. quintessential example of represented f = -kx -bv constant b , v velocity of object. represents spring being slowed down fluid (air/water/whatever like).

the minimal change code in case inside loop:

    cart.force=(k*(cart.x)-0.1*cart.vel.x)*vector(1,0,0) 

this produces underdamped system, try out overdamped system can set 0.1 10 instead.