You may have seen other versions of this, it's not an original idea, I copied a Javascript version, although just the idea, the code is all mine.
Basically it is a string of elastic with beads attached. You can bounce it around the screen. Try changing the constants, in small steps though.
+ Code Snippet`Elastic Physics Demo
`By Hamish McHaggis
`26/9/03
`This code demonstrates how to simulate the properties of elastic. I saw it first on a javascript mouse
`trail, I have recreated it without looking at any of the javascript code.
`The amount of gravity acting on the beads
#CONSTANT GRAVITY 0.04
`The decay of the X movement of the beads, 1=no decay, 0=complete decay
#CONSTANT XDECAY 0.97
`The decay of the Y movement of the beads, 1=no decay, 0=complete decay
#CONSTANT YDECAY 0.97
`The number of beads on the string take into account that each bead weighs the beads above it down
#CONSTANT NUMBEADS 10
`The elasticity of the X movement of the beads
#CONSTANT XELASTICITY 0.02
`The elasticity of the Y movement of the beads
#CONSTANT YELASTICITY 0.02
`The amount the bead movement decays when it hits a wall, 1=no decay, 0=complete decay
#CONSTANT WALLDECAY 0.9
`The between beads, before the string tenses and elasticity acts
#CONSTANT SLACKNESS 1
`The diameter of the beads
#CONSTANT BEADSIZE 6
`Screen mode
screenWidth as word = 800
screenHeight as word = 600
set display mode screenWidth,screenHeight,16
beadDist as float
beadDistX as float
beadDistY as float
distRatioX as float
distRatioY as float
sync on
sync rate 60
type beadType
X as float
Y as float
xMove as float
yMove as float
endtype
dim bead(NUMBEADS) as beadType
position mouse 0,0
do
`Draw background
ink rgb(255,255,255),0
box 0,0,screenWidth,screenHeight
`Position parent bead
bead(1).X=mousex()
bead(1).Y=mousey()
if bead(1).X-(BEADSIZE+10)/2<0 then bead(1).X=(BEADSIZE+10)/2
if bead(1).X+(BEADSIZE+10)/2>screenWidth then bead(1).X=screenWidth-(BEADSIZE+10)/2
if bead(1).Y-(BEADSIZE+10)/2<0 then bead(1).Y=(BEADSIZE+10)/2
if bead(1).Y+(BEADSIZE+10)/2>screenHeight then bead(1).Y=screenHeight-(BEADSIZE+10)/2
`Draw parent bead
ink rgb(0,0,0),0
circle bead(1).X,bead(1).Y,BEADSIZE
`Loop though other beads
for x=2 to NUMBEADS
`Work out X and Y distance between the bead and the one before it
beadDistX=bead(x).X-bead(x-1).X
beadDistY=bead(x).Y-bead(x-1).Y
`Work out total distance
beadDist=sqrt(beadDistX^2+beadDistY^2)
`If the beads are far enough apart, decrease the movement to create elasticity
if beadDist>SLACKNESS
dec bead(x).xMove,XELASTICITY*beadDistX
dec bead(x).yMove,YELASTICITY*beadDistY
endif
`If bead is not last bead
if x<>NUMBEADS
`Work out distances between the bead and the one after it
beadDistX=bead(x).X-bead(x+1).X
beadDistY=bead(x).Y-bead(x+1).Y
beadDist=sqrt(beadDistX^2+beadDistY^2)
`If the beads are far enough apart, decrease the movement to create elasticity
if beadDist>1
dec bead(x).xMove,XELASTICITY*beadDistX
dec bead(x).yMove,YELASTICITY*beadDistY
endif
endif
`Decay the movement of the beads to simulate loss of energy
bead(x).xMove=bead(x).xMove*XDECAY
bead(x).yMove=bead(x).yMove*YDECAY
`Apply gravity to bead movement
inc bead(x).yMove,GRAVITY
`Move beads
inc bead(x).X,bead(x).xMove
inc bead(x).Y,bead(x).yMove
`If the beads hit a wall, make them bounce off of it
if bead(x).X-(BEADSIZE+10)/2<0
bead(x).X=+(BEADSIZE+10)/2
bead(x).xMove=-bead(x).xMove*WALLDECAY
endif
if bead(x).X+(BEADSIZE+10)/2>screenWidth
bead(x).X=screenWidth-(BEADSIZE+10)/2
bead(x).xMove=-bead(x).xMove*WALLDECAY
endif
if bead(x).Y-(BEADSIZE+10)/2<0
bead(x).yMove=-bead(x).yMove*WALLDECAY
bead(x).Y=(BEADSIZE+10)/2
endif
if bead(x).Y+(BEADSIZE+10)/2>screenHeight
bead(x).yMove=-bead(x).yMove*WALLDECAY
bead(x).Y=screenHeight-(BEADSIZE+10)/2
endif
`Draw bead and string from it to the one before it
ink rgb(0,0,0),0
circle bead(x).X,bead(x).Y,BEADSIZE
ink rgb(200,100,0),0
line bead(x).X,bead(x).Y,bead(x-1).X,bead(x-1).Y
next x
text 20,20,str$(screen fps())
sync
cls
loop
Version 2
+ Code Snippet`Elastic Physics Demo 2.0
`By Hamish McHaggis
`26/9/03
`This code demonstrates how to simulate the properties of elastic. I saw it first on a javascript mouse
`trail, I have recreated it without looking at any of the javascript code.
`The amount of gravity acting on the beads
#CONSTANT GRAVITY 0.04
`The decay of the X movement of the beads, 1=no decay, 0=complete decay
#CONSTANT XDECAY 0.97
`The decay of the Y movement of the beads, 1=no decay, 0=complete decay
#CONSTANT YDECAY 0.97
`The number of beads on the string take into account that each bead weighs the beads above it down
#CONSTANT NUMBEADS 10
`The elasticity of the X movement of the beads
#CONSTANT XELASTICITY 0.02
`The elasticity of the Y movement of the beads
#CONSTANT YELASTICITY 0.02
`The amount the bead movement decays when it hits a wall, 1=no decay, 0=complete decay
#CONSTANT WALLDECAY 0.9
`The between beads, before the string tenses and elasticity acts
#CONSTANT SLACKNESS 1
`The diameter of the beads
#CONSTANT BEADSIZE 6
`Screen mode
screenWidth as word = 800
screenHeight as word = 600
set display mode screenWidth,screenHeight,16
beadDist as float
beadDistX as float
beadDistY as float
distRatioX as float
distRatioY as float
oX as float
oY as float
grabbedBead as integer
sync on
sync rate 60
type beadType
X as float
Y as float
xMove as float
yMove as float
fixed as boolean
endtype
dim bead(NUMBEADS) as beadType
position mouse 0,0
do
`Draw background
ink rgb(255,255,255),0
box 0,0,screenWidth,screenHeight
`If no bead is grabbed
if grabbedBead=0
`If mouse is clicked
if mouseclick()>0
`If LMB is clicked then detect whether to pick a bead
if mouseclick()=1
for x=1 to NUMBEADS
if sqrt((mousex()-bead(x).X)^2+(mousey()-bead(x).Y)^2)<=BEADSIZE
grabbedBead=x
position mouse bead(grabbedBead).X,bead(grabbedBead).Y
exit
endif
next x
else
`If RMB is clicked, pick bead 1
grabbedBead=1
position mouse bead(grabbedBead).X,bead(grabbedBead).Y
endif
endif
else
`If bead is grabbed...
`Store old bead position
oX=bead(grabbedBead).X
oY=bead(grabbedBead).Y
`Get new bead position
bead(grabbedBead).X=mousex()
bead(grabbedBead).Y=mousey()
`Bead movement=0
bead(grabbedBead).xMove=0
bead(grabbedBead).yMove=0
`If f is pressed fix/release the bead
if lower$(inkey$())="f"
if fHold=0
bead(grabbedBead).fixed=1-bead(grabbedBead).fixed
grabbedBead=0
fHold=1
endif
else
fHold=0
endif
`If mouse is released
if mouseclick()=0
`If object isn't fixed then give it momentum, so you can 'throw' the beads
if bead(grabbedBead).fixed=0
bead(grabbedBead).xMove=bead(grabbedBead).X-oX
bead(grabbedBead).yMove=bead(grabbedBead).Y-oY
endif
grabbedBead=0
endif
endif
`Loop though other beads
for x=1 to NUMBEADS
`If r is pressed release bead
if lower$(inkey$())="r" then bead(x).fixed=0
`If bead isn't fixed
if bead(x).fixed=0
if x<>1
`Work out X and Y distance between the bead and the one before it
beadDistX=bead(x).X-bead(x-1).X
beadDistY=bead(x).Y-bead(x-1).Y
`Work out total distance
beadDist=sqrt(beadDistX^2+beadDistY^2)
`If the beads are far enough apart, decrease the movement to create elasticity
if beadDist>SLACKNESS
dec bead(x).xMove,XELASTICITY*beadDistX
dec bead(x).yMove,YELASTICITY*beadDistY
endif
endif
`If bead is not last bead
if x<>NUMBEADS
`Work out distances between the bead and the one after it
beadDistX=bead(x).X-bead(x+1).X
beadDistY=bead(x).Y-bead(x+1).Y
beadDist=sqrt(beadDistX^2+beadDistY^2)
`If the beads are far enough apart, decrease the movement to create elasticity
if beadDist>1
dec bead(x).xMove,XELASTICITY*beadDistX
dec bead(x).yMove,YELASTICITY*beadDistY
endif
endif
`Decay the movement of the beads to simulate loss of energy
bead(x).xMove=bead(x).xMove*XDECAY
bead(x).yMove=bead(x).yMove*YDECAY
`Apply gravity to bead movement
inc bead(x).yMove,GRAVITY
`Move beads
inc bead(x).X,bead(x).xMove
inc bead(x).Y,bead(x).yMove
`If the beads hit a wall, make them bounce off of it
if bead(x).X-(BEADSIZE+10)/2<0
bead(x).X=+(BEADSIZE+10)/2
bead(x).xMove=-bead(x).xMove*WALLDECAY
endif
if bead(x).X+(BEADSIZE+10)/2>screenWidth
bead(x).X=screenWidth-(BEADSIZE+10)/2
bead(x).xMove=-bead(x).xMove*WALLDECAY
endif
if bead(x).Y-(BEADSIZE+10)/2<0
bead(x).yMove=-bead(x).yMove*WALLDECAY
bead(x).Y=(BEADSIZE+10)/2
endif
if bead(x).Y+(BEADSIZE+10)/2>screenHeight
bead(x).yMove=-bead(x).yMove*WALLDECAY
bead(x).Y=screenHeight-(BEADSIZE+10)/2
endif
ink rgb(0,0,0),0
else
ink rgb(255,0,0),0
endif
`Draw bead and string from it to the one before it
circle bead(x).X,bead(x).Y,BEADSIZE
ink rgb(200,100,0),0
if x<>1 then line bead(x).X,bead(x).Y,bead(x-1).X,bead(x-1).Y
next x
ink rgb(200,200,200),0
text 10,10,"FPS: "+str$(screen fps())
text 10,30,"Left Click to Grab a Bead"
text 10,45,"Right Click to Grab the First Bead"
text 10,60,"'F' to fix/release a bead in the air, while you are grabbing it"
text 10,75,"'R' to release all beads"
sync
cls
loop