Help with maths problem please..

; -------------------------------------------------------------------------------------------------------------------
; This subroutine animates the sphere.
; -------------------------------------------------------------------------------------------------------------------
.Animate_Sphere


	; Check to see if the entity collided with the level last frame.
	Entity_Hit = EntityCollided(ballpos, COLLIDE_Level)

	; If the entity collided with the level, then store the time of the last collision.	
	If Entity_Hit Then Last_Collide_Time = Time_Now 
					
	; Calculate motion friction:

		; Calculate the entity's current velocity.
		Velocity# = Sqr(Vx#^2 + Vy#^2 + Vz#^2)

		; If the entity is not traveling fast enough to be motion blurred:
		If Velocity# < 6.0
			
			; If motion blur is on, turn it off:
			If Motion_Blur = True

				SPS_DELETE_CHILD_EMITTERS(ballpos)
				Motion_Blur = False

			EndIf

		EndIf
		
		; If the entity is moving, adjust it's velocity:
		If Velocity# > 0 

			; Calculate the direction vector.
			; The direction vector has a length of 1.
			Direction_X# = Vx# / Velocity#
			Direction_Y# = Vy# / Velocity#
			Direction_Z# = Vz# / Velocity#

			; Compute air friction.
			; Air friction is dependent on the speed of the entity, and will prevent it from accelerting forever.
			Air_Friction_Force# = AIR_FRICTION_CONSTANT# * Velocity#^2.0	
			Velocity# = Velocity# - (Air_Friction_Force# * Time_Delta_Sec#)
	
			; If the entity is colliding with the level this frame, or still sticking to the level from it's last
			; collision, then apply ground friction.
			If (Time_Now - Last_Collide_Time) <= Player_Friction_Stick_Time 

				; Compute ground friction.  Ground friction is not dependent on the speed of the entity.
				Velocity# = Velocity# - (GROUND_FRICTION_CONSTANT# * Time_Delta_Sec#)

			EndIf


			; Make sure the entity's velocity doesn't go below 0.
			; It is impossible to have a negative velocity in physics and "bad things" happen if you try to.
			If (Velocity# < 0) Then Velocity# = 0			


			; Convert the entity's velocity and direction back into a motion vector.
			Vx# = Direction_X# * Velocity#
			Vy# = Direction_Y# * Velocity#
			Vz# = Direction_Z# * Velocity#


			; If the entity collided with the level, make it bounce.
			If Entity_Hit > 0 

				; Calculate bounce:

	    			; Get the normal of the surface which the entity collided with.    
					Nx# = CollisionNX(ballpos, 1)
					Ny# = CollisionNY(ballpos, 1)
					Nz# = CollisionNZ(ballpos, 1)
		
				; Multiply the entity's motion vector by the surface normal.
				; This gives us the part of the vector which points in the same direction as the surface the object collided with.

					Elasticity# = 0.5 

					Vx# = Vx# - Vx#*Abs(Nx#)*(1.0 - Elasticity#)
					Vy# = Vy# - Vy#*Abs(Ny#)*(1.0 - Elasticity#)
					Vz# = Vz# - Vz#*Abs(Nz#)*(1.0 - Elasticity#)
			
				; Compute the dot product of the entity's motion vector and the normal of the surface collided with.
					VdotN# = Vx#*Nx# + Vy#*Ny# + Vz#*Nz#
							
				; Calculate the normal force.
					NFx# = -2.0 * Nx# * VdotN#
					NFy# = -2.0 * Ny# * VdotN#
					NFz# = -2.0 * Nz# * VdotN#

				; Add the normal force to the direction vector.
					Vx# = Vx# + NFx#
					Vy# = Vy# + NFy#
					Vz# = Vz# + NFz#
	
				; Do not allow the entity to move vertically.
				;	If Vy# > 0 Then Vy# = 0
	
			EndIf


		EndIf

	
	; Apply directional thrust:

		; If the entity collided with the level, apply directional thrust.
		;If Entity_Hit > 0 
		
			; Take thrust in object space, and translates it to an XYZ vector in world space.
			;TFormVector 0, 0, Thrust#, ballpos, 0

			; Add any thrust being applied this frame.
			; There's a very good reason why this is done AFTER the friction is calculated.
			; It involves inequalities in force cause by variable framerates.
			Vx# = Vx# + (Thrust_X# * Time_Delta_Sec#)
			Vz# = Vz# + (Thrust_Z# * Time_Delta_Sec#)

		;EndIf


	; Apply gravity:
		Vy# = Vy# - (GRAVITY# * Time_Delta_Sec#)


	; Move and rotate the entity:

		; We rotate the entity by the actual distance moved and not by the velocity because if we rotate according
		; to the velocity then the entity will roll when it's up against a wall and not moving.

		OldX# = NewX#
		OldZ# = NewZ#

		TranslateEntity ballpos, Vx#*Time_Delta_Sec#, Vy#*Time_Delta_Sec#, Vz#*Time_Delta_Sec#, True

		NewX# = EntityX#(ballpos, True)
		NewZ# = EntityZ#(ballpos, True)
		
		Mx# = (NewX# - OldX#)
		Mz# = (NewZ# - OldZ#)		

		; Rotate the entity the right amount for it's radius and the distance it has moved along the X and Z axis.
		; This is kinda a hack and only designed for rolling on planes but you won't notice the diffrence.
		XAngleAdjust# = (Mx# / BallRadius#) * (180.0/Pi) 
		ZAngleAdjust# = (Mz# / BallRadius#) * (180.0/Pi)
	    TurnEntity ball,ZAngleAdjust#,0,-XAngleAdjust#,True


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