SCREEN 12
pi = ATN(1) * 4
WINDOW (-160, 120)-(160, -120)

beta = .6

opnieuw:
LOCATE 1, 1: PRINT USING "velocity: ##.##c"; beta
gama = 1 / SQR(1 - beta * beta)
t0 = 50
t = t0 / gama
LINE (-2 * t0, 0)-(2 * t0, 0)
LINE (0, -2 * t0)-(0, 2 * t0)
tra = t / (1 + beta)
xra = -beta * tra
trb = t * (1 - 2 * beta) / (1 - beta)
xrb = -t + trb
LINE (0, 0)-(0, t), 6: LINE -(0, 2 * t), 2
LINE (0, 0)-(xra, tra), 6
LINE -(0, t), 0: LINE -(xra, tra), 8
LINE -(xrb, trb), 5
LINE -(0, 2 * t), 2
LINE (0, 0)-(-xra, t), 12
LINE -(0, t), 0: LINE -(-xra, t), 8
LINE -(-xrb, t), 5
LINE -(0, 2 * t), 9
CIRCLE (0, t), 1, 13:
'CIRCLE (0, 2 * t), 1, 9
wacht:
SLEEP: a$ = INKEY$
SELECT CASE a$
CASE "+": IF beta < .98 THEN beta = beta + .01
CASE "-": IF beta > .02 THEN beta = beta - .01
CASE " ": END
CASE ELSE: GOTO wacht
END SELECT
CLS
GOTO opnieuw
END

END