10  REM PROGRAM NAME = CENTRI, BEGINS - FORCE TO STILL MASS
20  REM CHAINED TO CENTRQ, CENTR2, CENTR3
30  GOTO 50
40  CHAIN "$CENTR2"
50  DIM X$[30]
60  X$="123456789"
70  X=0
80  PRINT "THIS SIMULATES A STROBOSCOPIC PHOTOGRAPH OF THE MOTION OF A FREE MASS"
90  PRINT "WHILE A UNIFORM FORCE IS APPLIED TO IT."
100  PRINT 
110  PRINT "-----SECTION 1:"'10
120  PRINT "BEGIN WITH A MASS WHICH IS MOTIONLESS."
130  PRINT "IN WHICH DIRECTION DO YOU WANT TO APPLY A FORCE ?"
140  X=X+1
150  PRINT 
160  PRINT "--PART "X$[X,X]":  EAST, SOUTH, OR WEST?  ";
170  DIM A$[10]
180  ENTER 100,W,A$
190  PRINT 
200  IF A$#"EAST" THEN 230
210  A=1
220  GOTO 280
230  IF A$#"SOUTH" THEN 260
240  A=2
250  GOTO 280
260  IF A$#"WEST" THEN 160
270  A=3
280  PRINT '10"----SIMULATED PHOTOGRAPH:"'10
290  GOSUB A OF 380,420,440
300  PRINT 
310  PRINT "DO YOU WANT TO TRY ANOTHER FORCE?  ";
320  DIM B$[10]
330  ENTER 100,W,B$
340  PRINT 
350  IF B$="YES" THEN 140
360  IF B$="NO" THEN 700
370  GOTO 310
380  FOR N=1 TO 5
390  PRINT TAB(N^2);"*";
400  NEXT N
410  GOTO 480
420  PRINT "*"'13'10'10"*"'13'10'10'10"*"'13'10'10'10'10"*"'13'10'10'10'10'10"*"
430  GOTO 480
440  FOR N=1 TO 5
450  PRINT TAB(25-N^2);"*"'13;
460  NEXT N
470  GOTO 480
480  PRINT 
490  PRINT 
500  PRINT "THE DIRECTION OF THE FORCE IS "A$"."
510  PRINT "IN WHICH DIRECTION IS THE RESULTING VELOCITY?  ";
520  DIM C$[10]
530  ENTER 200,W,C$
540  PRINT 
550  IF C$=A$ THEN 580
560  GOSUB 680
570  GOTO 510
580  PRINT "     RIGHT!"
590  PRINT "IN WHICH DIRECTION IS THE POSITIVE ACCELERATION?  ";
600  ENTER 100,W,C$
610  PRINT 
620  IF C$=A$ THEN 650
630  GOSUB 680
640  GOTO 590
650  PRINT "     RIGHT!"
660  PRINT 
670  RETURN 
680  PRINT "     WRONG. EXAMINE THE SIMULATED PHOTOGRAPH AND TRY AGAIN."
690  RETURN 
700  PRINT 
710  GOTO 40
720  END 
