Backspin effect in pool game with SceneKit - scenekit

Question

I would like to create a realistic pool game and to implement at least some basic ball effects. I started from scratch with SceneKit and at this point I'm just studying the proper technology to go with it.SceneKit would be the ideal.
I managed to achieve an acceptable ball effect for sidespin and some sort of forward spin. The one I'm struggle with is backspin. I'm playing around with the position parameter of applyForce method, but it seems that alone will not give me the result I'm looking for. Either I'm missing something (I've got limited knowledge of physics) or SceneKit's physics simulation is just not enough for what I want. Basically I have a sphere of 1.5 radius and I went from -1.5 to 1.5 on Y component for the position vector and the result is either the white ball or the ball I'm hitting jumps when collision occurs.
The first screenshot shows the moment of impact whilst the latter shows after the collision and how it jumps.
The two spheres are configured like this
let sphereGeometry = SCNSphere(radius: 1.5)
sphere1 = SCNNode(geometry: sphereGeometry)
sphere1.position = SCNVector3(x: -15, y: 0, z: 0)
sphere2 = SCNNode(geometry: sphereGeometry)
sphere2.position = SCNVector3(x: 15, y: 0, z: 0)
And the code that gives me that effect is the following:
sphere1.physicsBody?.applyForce(SCNVector3Make(350, 0, 0), atPosition:SCNVector3Make(1.5, -0.25, 0), impulse: true)
What I'm trying to do in that code is to hit the ball roughly a bit below the center. How I got to -0.25 was to get an angle of 10 degrees and calculate its sin function. Then I multiplied it by sphere radius so I can get a point that lies right on the sphere's surface.

Answer 1

So I've been reading several papers/chapters about pool physics and I think I found something that at least proves me I can do it with SceneKit. So what I was missing was i. right formulae ii. angular velocity. The physics still need a lot of polish but at least it seems to get roughly the trajectory one would expect when applying these effects. Here's the code in case anyone's interested in:
//Cue strength
let strength : Float = 1000
//Cue mass expressed in terms of ball's mass
let cueMass : Float = self.balls[0].mass * 1.25
//White ball
let whiteBall = self.balls[0]
//The ball we are trying to hit
let targetBall = self.balls[1]
//White ball radius
let ballRadius = whiteBall.radius
//This should be in the range of {-R, R} where R is the ball radius. It determines how much off the center we would like to hit the ball along the z-axis. Produces left/right spin
let a : Float = 0
//This should be in the range of {-R, R} where R is the ball radius. It determines how much off the center we would like to hit the ball along the y-axis. Produces top/back spin
let b : Float = -ballRadius * 0.7
//This is calculated based off a and b and it is the position that we will be hitting the ball along the x-axis.
let c : Float = sqrt(ballRadius * ballRadius - a * a - b * b)
//This is the angle of the cue expressed in degrees. Values greater than zero will produce jump shots
let cueAngle : Float = 0
//Cue angle in radians for math functions
let cueAngleInRadians : Float = (cueAngle * 3.14) / 180
let cosAngle = cos(cueAngleInRadians)
let sinAngle = sin(cueAngleInRadians)
//Values to calculate the magnitude to be applied given the above variables
let m0 = a * a
let m1 = b * b * cosAngle * cosAngle
let m2 = c * c * sinAngle * sinAngle
let m3 = 2 * b * c * cosAngle * sinAngle
let w = (5 / (2 * ballRadius * ballRadius)) * (m0 + m1 + m2 + m3)
let n = 2 * whiteBall.mass * strength
let magnitude = n / (1 + whiteBall.mass / cueMass + w)
//We would like to point to the target ball
let targetVector = targetBall.position
//Get the unit vector of our target
var target = (targetVector - whiteBall.position).normal
//Multiply our direction by the force's magnitude. Y-axis component reflects the angle of the cue
target.x *= magnitude
target.y = (magnitude / whiteBall.mass) * sinAngle
target.z *= magnitude
//Apply the impulse at the given position by c, b, a
whiteBall.physicsBody?.applyForce(target, atPosition: SCNVector3Make(c, b, a), impulse: true)
//Values to calculate angular force
let i = ((2 / 5) * whiteBall.mass * ballRadius * ballRadius)
let wx = a * magnitude * sinAngle
let wy = -a * magnitude * cosAngle
let wz = -c * magnitude * sinAngle + b * magnitude * cosAngle
let wv = SCNVector3Make(wx, wy, wz) * (1 / i)
//Apply a torque
whiteBall.physicsBody?.applyTorque(SCNVector4Make(wv.x, wv.y, wv.z, 0.4), impulse: true)
Note that values of a, b, c should take into account the target vector's direction.