10 REM PROGRAM PISTON
20 REM IMPACT USES CENTER OF MASS COORDINATES
40 DIM X(41), Y(41), U(41), V(41), CTR(41)
50 DIM A(100), B(200)
60 G = .001: MPIS = 10: KE = 0: TK0 = 273.15
70 U0 = .04: TSEC = 0: TSECMAX = 2500
75 IF NCH = 1 THEN 240
80 CLS : SCREEN 12: COLOR 10
90 LOCATE 3, 32: PRINT "MOVING MOLECULES"
100 LOCATE 5, 39: PRINT "BY"
110 LOCATE 7, 29: PRINT "STANLEY DAVID GEDZELMAN"
120 GOSUB 1580
150 LOCATE 10, 19: PRINT "THIS PROGRAM SHOWS HOW MOVING GAS MOLECULES"
160 LOCATE 11, 20: PRINT "CREATE TEMPERATURE, PRESSURE, AND DENSITY"
170 GOSUB 1580: COLOR 12
180 LOCATE 16, 5: PRINT "PARAMETERS YOU CHOOSE"
190 LOCATE 18, 5: PRINT "1. TEMPERATURE (GAS KINETIC ENERGY)"
200 LOCATE 19, 5: PRINT "2. NUMBER OF MOLECULES  (GAS DENSITY)"
210 LOCATE 20, 5: PRINT "3. CHANGE OF TEMPERATURE"
220 LOCATE 21, 5: PRINT "4. CHANGE OF DENSITY"
225 GOSUB 1580
230 COLOR 9: LOCATE 25, 28: PRINT "HIT ANY KEY TO CONTINUE"
235 WHILE INKEY$ = "": WEND
240 CLS : COLOR 14
250 PRINT "SELECT INITIAL NUMBER OF MOLECULES "
260 PRINT "    MINIMUM = 10   MAXIMUM = 40"
270 PRINT
280 INPUT "    NUMBER OF MOLECULES = ", NMOL1
290 NMOL = NMOL1
300 PRINT "": COLOR 11: PRINT "SELECT INITIAL TEMPERATURE (KELVIN)"
310 PRINT "  MINIMUM = 100   MAXIMUM = 800"
320 PRINT
330 INPUT "    TEMPERATURE = ", T0: T = T0
340 VCON = SQR(T / TK0)
345 KE0 = (VCON * U0 * NMOL) ^ 2: REM INITIAL KE
350 PRINT "": COLOR 12
360 PRINT " TEMPERATURE CHANGE OPTION"
370 PRINT " TYPE 1 TO MAKE TEMPERATURE FALL"
380 PRINT " TYPE 2 TO KEEP TEMPERATURE SAME"
390 PRINT " TYPE 3 TO MAKE TEMPERATURE RISE"
400 INPUT "ENTER YOUR CHOICE  = ", TCH
410 DT = 1 + (TCH - 2) / 50
420 IF DT = 1 THEN 430 ELSE 500
430 COLOR 13: PRINT ""
440 PRINT " DENSITY CHANGE OPTION"
450 PRINT " TYPE 1 TO REMOVE MOLECULES"
460 PRINT " TYPE 2 TO KEEP MOLECULES"
470 PRINT " TYPE 3 TO ADD MOLECULES"
480 INPUT "ENTER YOUR CHOICE = ", NCH
490 DN = NCH - 2
495 COLOR 9: LOCATE 25, 25: PRINT "PRESS ANY KEY TO START MOLECULES"
497 WHILE INKEY$ = "": WEND
500 CLS : COLOR 15
510 REM DRAW MOLECULES AND PISTON WALL
520 CIRCLE (100, 100), 1
530 PAINT (100, 100)
540 GET (99, 99)-(101, 101), A
550 PUT (99, 99), A, XOR
560 LINE (40, 48)-(98, 50), 5, BF
570 GET (40, 48)-(98, 50), B
580 PUT (40, 48), B, XOR
600 R = R + 1
620 RANDOMIZE R
640 LOCATE 1, 1: PRINT "TEMP    = "; T0
660 LOCATE 1, 35: PRINT "NUMBER OF MOLECULES = "; NMOL
670 LOCATE 4, 3: PRINT "TIME = "
680 LOCATE 2, 1: PRINT "DENSITY = "
690 REM SET INITIAL POSITION AND SPEED OF BALLS
700 REM POSITION X HORIZONTAL, Y VERTICAL
710 REM SPEED U HORIZONTAL, V VERTICAL
720 REM YPIS IS PISTON LOCATION
730 G = G * NMOL
740 YPIS = 470 - 2 * NMOL * T / TK0
750 IF YPIS > 420 THEN YPIS = 420
760 FOR I = 1 TO 41
770 X(I) = INT(50 * RND(R)) + 295
780 U(I) = U0 * NMOL * VCON * SQR(RND(R))
790 V(I) = U0 * NMOL * VCON * SQR(RND(R))
800 IF RND(R) - .5 < 0 THEN U(I) = -U(I)
810 IF RND(R) - .5 < 0 THEN V(I) = -V(I)
820 IF I > NMOL THEN Y(I) = 470: GOTO 840
830 Y(I) = INT((468 - YPIS) * RND(R)) + YPIS + 3
840 NEXT I
850 FOR I = 1 TO NMOL
860 KE = KE + V(I) ^ 2
870 NEXT I
910 LINE (285, 80)-(290, 480), 2, BF
920 LINE (350, 80)-(355, 480), 2, BF
930 LINE (285, 475)-(355, 480), 2, BF
940 PUT (291, YPIS), B, XOR
950 FOR I = 1 TO NMOL
960 PUT (X(I), Y(I)), A, XOR
970 NEXT I
980 VP1 = VPIS
990 TSEC = TSEC + 1
1000 LOCATE 2, 10: PRINT CINT(350 * NMOL / (475 - YPIS)) / 100
1010 LOCATE 4, 9: PRINT TSEC
1020 FOR I = 1 TO NMOL
1030 PUT (X(I), Y(I)), A, XOR
1040 REM IF BALLS REACH SIDE WALLS REVERSE U
1050 IF X(I) > 346 THEN U(I) = -ABS(U(I))
1060 IF X(I) < 292 THEN U(I) = ABS(U(I))
1070 IF Y(I) < YPIS + 4 AND V(I) < VPIS THEN GOSUB 1210
1080 IF Y(I) > 471 THEN V(I) = -ABS(V(I))
1090 X(I) = X(I) + U(I)
1100 Y(I) = Y(I) + V(I)
1110 PUT (X(I), Y(I)), A, XOR
1120 NEXT I
1130 REM PISTON MOVEMENT CALCULATIONS
1140 PUT (291, YPIS), B, XOR
1150 VPIS = VPIS + G
1160 YPIS = YPIS + (VP1 + VPIS) / 2
1165 IF YPIS < 80 THEN SOUND 100, 9: GOTO 1610
1170 PUT (291, YPIS), B, XOR
1180 IF TSEC = INT(TSEC / 5) * 5 THEN 1250
1190 GOTO 980
1200 REM PISTON IMPACTS -CENTER OF MASS COORDINATES
1210 VCG = (MPIS * VPIS + V(I)) / (MPIS + 1)
1220 V(I) = -V(I) + 2 * VCG + G / (MPIS + 1)
1230 VPIS = -VPIS + 2 * VCG
1240 RETURN
1250 IF TSEC > TSECMAX THEN 1610
1260 KE = 0
1280 FOR I = 1 TO NMOL
1300 KE = KE + U(I) ^ 2 + V(I) ^ 2
1302 IF V(I) <> 0 THEN QQ = ABS(U(I) / V(I)) ELSE QQ = 1: REM EQUIPARTITION
1304 U(I) = U(I) / QQ
1306 V(I) = V(I) * QQ
1310 NEXT I
1330 LOCATE 1, 10: PRINT CINT(T0 * KE * NMOL1 ^ 2 / (KE0 * NMOL ^ 3))
1340 IF NMOL < 10 THEN 980
1350 IF DT = 1 THEN 1430
1360 FOR I = 1 TO NMOL
1370 U(I) = U(I) * SQR(DT)
1380 V(I) = V(I) * SQR(DT)
1390 NEXT I
1400 T = T * DT
1410 REM LOCATE 1, 8: PRINT CINT(T)
1420 GOTO 980
1430 IF DN = 0 THEN 980
1440 IF NMOL > 40 THEN 980
1450 IF DN < 0 THEN PUT (X(NMOL), Y(NMOL)), A, XOR
1460 PVCH = (NMOL + DN) / NMOL
1470 NMOL = NMOL + DN
1480 FOR I = 1 TO 40
1490 U(I) = U(I) * PVCH
1500 V(I) = V(I) * PVCH
1510 NEXT I
1520 IF DN > 0 THEN PUT (X(NMOL), Y(NMOL)), A, XOR
1530 G = G * PVCH
1540 LOCATE 1, 57: PRINT NMOL
1550 GOTO 980
1560 END
1570 REM TIME DELAY LOOP
1580 FOR I = 1 TO 20000
1590 NEXT I
1600 RETURN
1610 CLS : NCH = 1
1620 PRINT "DO YOU WANT TO DO ANOTHER EXPERIMENT?"
1630 PRINT
1640 PRINT "TYPE Y OR N "
1650 Y$ = INKEY$: IF Y$ = "Y" OR Y$ = "y" THEN 40
1660 IF Y$ = "N" OR Y$ = "n" THEN 1670 ELSE 1650
1670 CLS : LOCATE 10, 33: PRINT "THATS ALL FOLKS"
1680 END