Mouvement affine vitesse uniforme

import tkinter as tk
from random import randint
from math import sqrt

fen = tk.Tk()

can = tk.Canvas(fen, width=300, height=300, bg='#000')
can.pack()

class point:
    
    def __init__(self, x, y, c):
        # Point
        self.e = 5
        self.p = can.create_oval(x-self.e, y-self.e, x+self.e, y+self.e, fill=c)

        # Trajectoire
        self.a = -1*randint(0,5)/[1, 10][randint(0,1)]
        self.b = y
     
class trajectoire1(point):

    def __init__(self, x, y):
        point.__init__(self, x, y, '#00f')
        
        self.x = x
        
        self.update()

    def update(self):
        (x1, y1, x2, y2) = can.coords(self.p)
        self.x += 1

        y = self.a*self.x + self.b
        can.coords(self.p, self.x-self.e, y-self.e, self.x+self.e, y+self.e)

        fen.after(50, self.update)

class trajectoire2(point):

    def __init__(self, x, y):
        point.__init__(self, x, y, '#f00')
        self.update()

    def Intersection(self, a, b, Xc, Yc, R, w):
        """
        C(Xc;Yc;R)
        |  (x-Xc)^2 + (y-Yc)^2 = R^2
        |  y = ax+b

        x^2(1+a^2) + x(-2*Xc +2*a*b -2*a*Yc) + (Xc^2 +Yc^2 +b^2 -2*b*Yc -R^2) = 0
        """
        A, B, C = 1+pow(a,2), -2*Xc +2*a*b -2*a*Yc, pow(Xc,2)+pow(Yc,2)+pow(b,2)-2*b*Yc-pow(R,2)
        D = pow(B,2)-4*A*C

        return( [(-B-sqrt(D))/(2*A), (-B+sqrt(D))/(2*A)][w] )

    def update(self):
        (x1, y1, x2, y2) = can.coords(self.p)

        x = self.Intersection(self.a, self.b, (x1+x2)/2, (y1+y2)/2, 2, 1)
        y = self.a*x + self.b
        
        can.coords(self.p, x-self.e, y-self.e, x+self.e, y+self.e)

        fen.after(50, self.update)
        
def add():
    for h in range(2):
        trajectoire1(0, 300)
        trajectoire2(0, 300)

    fen.after(10000, add)
add()
    
fen.mainloop()