How to do physics?

Strict 
Graphics 1024,768
Global SpringList:TList=New TList
 
Global Index:Int 
Global Particles:Tparticle[20]

Global DD:Int
Global EE:Int
Global SpringStrength:Float=55.15
Type Tparticle

	Field Image:Timage
	Field X:Float
	Field Y:Float
	Field XS:Float
	Field YS:Float
	Field Locked:Int

	Function Create:TParticle(X:Int,Y:Int)
    		Local P:Tparticle
		P:Tparticle= New TParticle
		P.X=X
		p.Y=Y
    		Return P
	End Function
	Function Update()
		For Local Index=0 To 5
		Particles[Index].YS:+.98
		Particles[Index].XS:*.90
		Particles[Index].YS:*.90
		Particles[Index].X:+Particles[Index].XS
		Particles[Index].Y:+Particles[Index].YS
		If Particles[Index].Y>765 And Particles[Index].YS>0.0
			Particles[Index].YS=-Particles[Index].YS*.98
			Particles[Index].Y=765.0
		End If 
		
		DrawOval(Particles[Index].X-3,Particles[Index].Y-3,6,6)
                next
	End Function 
End Type 

Type TSpring

	Field Connection1
	Field Connection2
	Field Length:Float
	Field CurrentLenght:Float
	Field PeakTension:Float
	
	Function Create:TSpring(C1:Int,C2:Int)
    		Local S:TSpring
		Local DX:Float
		Local DY:Float
		S:TSpring= New TSpring
		S.Connection1=C1
		S.Connection2=C2
		DX=Particles[C1].X-Particles[C2].X
		DY=Particles[C1].Y-Particles[C2].Y
		S.Length=Sqr((DX*DX)+(DY*DY))	 	
   	 	ListAddLast SpringList,S
	Return S
	End Function
	Function Update()
		For Local Spring:Tspring=EachIn SpringList
		Local P1=Spring.Connection1
		Local P2=Spring.Connection2
		Local SX:Float = Particles[P1].X-Particles[P2].X
		Local SY:Float = Particles[P1].Y-Particles[P2].Y
		Local Length:Float =Sqr((SX*SX)+(SY*SY))
		Spring.CurrentLenght=Length
		Local NormalLength:Float=Spring.Length
		Local ForceScaler:Float=(Length-NormalLength)/NormalLength
		SX:*(1.0/Length)
		SY:*(1.0/Length)
		Local FX:Float = SX*ForceScaler
		Local FY:Float = SY*ForceScaler
		FX:*SpringStrength
		FY:*SpringStrength
		Local FX2:Float=-FX
		Local FY2:Float=-FY
		
		Particles[P2].XS:+FX
		Particles[P2].YS:+FY
		Particles[P1].XS:-FX 
		Particles[P1].YS:-FY 
		DrawLine(Particles[Spring.Connection1].X,Particles[Spring.Connection1].Y,Particles[Spring.Connection2].X,Particles[Spring.Connection2].Y)
 		Next 
	End Function 
End Type 

RestoreData Parts
For Index=0 To 5
	ReadData DD,EE
	Particles[Index]=TParticle.Create(DD,EE )
Next 
 
RestoreData Springs
For Index=0 To 8
	ReadData DD,EE
	Tspring.Create(DD,EE)
Next 
 
Repeat 
	Cls
 	If MouseDown (1)
		 Local Index=5
		 Particles[Index].YS:+((MouseY()-Particles[Index].Y)/25)
		 Particles[Index].XS:+((MouseX()-Particles[Index].X)/50) 
	End If
	Tparticle.Update() 
	TSpring.Update()
	If KeyDown(Key_A)
		SpringStrength:+.1
	End If 
	If KeyDown(Key_Z)
		SpringStrength:-.1
	End If 
 	DrawText ("Spring Tension A/Z "+SpringStrength,0,24)
	DrawText ("Click the Mouse",0,36)
	Flip
Until KeyHit(Key_Escape)

#Parts 
DefData 500,100
DefData 600,100
DefData 600,200
DefData 500,200
DefData 550,150
DefData 550,10 

#Springs
DefData 0,5,5,1,1,0,0,3,3,2,2,1,1,3,2,4,0,2