Durham Hackathon

How about balls which aren’t perfectly elastic?

A real ball will never be perfectly elastic. That means when it collides with something, the wall or another ball, it will lose some kinetic energy. This energy is lost for example as sound and heat. We can simulate this by reducing the velocity.

How does the simulation change when you change the loss of energy?
What numbers are actually realistic? Have a look here for numbers for some common materials.

Add bounce:

import turtle
import random

# We will need the edges of our box, so we set them
width = 300
height = 400
window = turtle.Screen()
window.setup(width, height)
window.tracer(0)

color = ["blue",
        "yellow",
        "red",
        "darkgreen", 
        "cyan", 
        "violet",
        "magenta",
        "orange",
        "purple", 
        "navy", 
        "brown", 
        "maroon",
        "turquoise", 
        "lightgreen", 
        "green", 
        "skyblue", 
        "black", 
        "gold",
        "gray"]

N = 10 # Number of balls
balls = [] # A list to hold the balls
mass = []  # A list to hold masses of the balls

# Set up N balls and start them in random positions
for i in range(N):
    # Now the balls also have a mass
    mass.append(random.randint(1,4))

balls.append(turtle.Turtle())
    balls[i].penup()
    balls[i].shape("circle")
    balls[i].shapesize(mass[i]**0.5)
    balls[i].color(color[i%len(color)])

# Set random starting position
    balls[i].setx(random.randint(0,height / 4))
    balls[i].sety(random.randint(0,height / 4))

# Earth's gravitational constant
g = -9.81

# Timestep size
t = 0.08

# Starting velocity is now also a list, we need one velocity per ball
ux = []
uy = []
for i in range(N):
    ux.append(random.randint(-width/10,width/10))
    uy.append(0)

while True:
    for i in range(N):
        uy[i] += g*t
        balls[i].setx(ux[i]*t + balls[i].xcor())
        balls[i].sety(uy[i]*t + balls[i].ycor())

if balls[i].ycor() < -height / 2 or balls[i].ycor() > height / 2:
            uy[i] = -uy[i]
        if balls[i].xcor() < -width / 2 or balls[i].xcor() > width / 2:
            ux[i] = -ux[i]

# Check for collisions
        for j in range(N):
            if i != j and \
            abs(balls[i].xcor() - balls[j].xcor()) < 10 and \
            abs(balls[i].ycor() - balls[j].ycor()) < 10:
                uxh = ux[i]
                uyh = uy[i]
                ux[i] = ux[j]
                uy[i] = uy[j]
                ux[j] = uxh
                uy[j] = uyh
    window.update()

Fancy a hint? You can find the solution here.