Sim is a pretty big group, with a lot of variables that govern the simulation. You can set the accuracy of the sim, and influences like friction. You can also define if some parts of the physics engine should be used or not. A lot of these variables concernes the inner workings of the Phun physics solver. Touch at your own peril!

Variable name	Variable type	Description	Default(beta 4.22)
adHocSolver	true or false	if true, switches from SPOOK to a different and more basic solver. default is false	false
airDensity	positive decimal value	density of the air	0.01
airFrictionLinear	positive decimal value	linear friction of the air	0.01
airFrictionQuadratic	positive decimal value	quadratic friction of the air	0.0
airSwitch	true or false	whether air friction is enabled or not	true
defaultBodyDensity	positive decimal value	default density of objects	2.0
defaultBodyFriction	positive decimal value	default friction of objects	0.5
defaultBodyRestitution	positive decimal value	default bounciness of objects	0.5
fallLimit	positive decimal value	the limit of when an object gets deleted after falling outside of the screen	1000.0
gravity	array of two decimal values	X and Y force of gravity	[0.0, -9.8]
gravitySwitch	true or false	whether gravity is enabled or not	true
leapFrog	true or false	if false, switches to euler integration instead of leap-frog. true by default.	true
maxPositionCorrection	positive decimal value	sets the maximum penetration used when applying impulses in constraint violations. Set to infinity by default.	+inf
prioritizedSolver	true or false	if set to true, will yield a more stable, but far slower, constraint solver.	false
rotFrictionLinear	positive decimal value	linear rotational friction	0.01
running	true or false	whether the simulation is running or not	false
solveAccFactor	positive decimal value	sets how much the solver will conuter-act acceleration differences between two constrained bodies. Set to 1 by default. Don't touch.	1.0
solveConstant	positive decimal value	Affects the SPOOK solver. Don't touch!	100000000
solveDconstraints	positive decimal value	The number of time steps the SPOOK solver will aim to satisfy a hinge contraint within. A low number means faster convergence; a high number means more damped and stable simulation.	5.0
solveDcontacts	positive decimal value	The number of time steps the SPOOK solver will aim to satisfy c contact within. A low number means faster convergence; a high number means more damped and stable simulation.	5.0
solveDistFactor	positive decimal value	sets how much the solver will conuter-act penteration in constraint violation. Set to 1 by default. Don't touch.	1.0
solveIter	positive integer value	the number of constraint solving iterations. A higher number means a more stable simulation.	30
solvePenetrationDamping	true or false	not used.	false
solvePreSortConstraints	true or false	sets if the constraints will be ordered by violation amount before solving them. true by default.	true
solveRegularizationFactor	positive decimal value	Affects the amount of regalurization in the SPOOK solver. Set to 1 by default.	1.0
solveVelFactor	positive decimal value	sets how much the solver will conuter-act velocity differences between two constrained bodies. Set to 1 by default. Don't touch.	1.0
springForce	positive decimal value	this is the value by which spring strengths are multiplied. Alterning this will change the strength of all springs.	1000.0
targetPenetration	positive decimal value	sets how much penetration is allowed in a contact	0.001
time	constant positive decimal value	number of seconds the simulation has been running
timeDelta	positive decimal value	time between two physics engine solvings	0.01
timeFactor	positive decimal value	sets the simulation speed. A value of 1 means realtime.	1.0
warmStart	true or false	whether or not to apply forces at sim start	true
warmStartFactor	positive decimal value	multiplication value of warm-start forces existing at sim start	0.5