Make Node Dynamic for Only One Object Swift and Spritekit - ios

Question

I am creating a space shooter game, and I want to make one of my nodes only be dynamic when it interacts with ones specific node, as opposed to all nodes. Essentially, I only want the node to act as dynamic when it interacts with one specified node. How can I do this?
Thanks.
I know the question is a but confusing, but if anyone has any ideas it would be extremely helpful!!
let Bullet = SKSpriteNode(imageNamed: "BulletGalaga.png")
Bullet.zPosition = -5
Bullet.position = CGPoint(x: ship.position.x, y: ship.position.y)
Bullet.zRotation = ship.zRotation
//let action = SKAction.moveTo(CGPointMake(400 * cos(Bullet.zRotation),(400 * -sin(Bullet.zRotation))), duration: 0.8)
let action = SKAction.move(
to: CGPoint(
x: 1200 * -cos(Bullet.zRotation - 1.57079633) + Bullet.position.x,
y: 1200 * -sin(Bullet.zRotation - 1.57079633) + Bullet.position.y
),
duration: 2.4)
//let action = SKAction.moveToY(self.size.height + 30, duration: 0.8)
//let action = SKAction.moveTo(self.ship.size.height, duration: 0.8)
let actionDone = SKAction.removeFromParent()
Bullet.run(SKAction.sequence([action, actionDone]), withKey: "bulletAction")
Bullet.physicsBody = SKPhysicsBody(rectangleOf: Bullet.size)
Bullet.physicsBody?.affectedByGravity = false
Bullet.physicsBody?.isDynamic = false
self.addChild(Bullet)
I added this:
ship.physicsBody?.categoryBitMask = shipCategoryBitMask
Bullet.physicsBody?.categoryBitMask = bulletCategoryBitMask
enemy.physicsBody?.categoryBitMask = enemyCategoryBitMask
enemyBullet.physicsBody?.categoryBitMask = enemyBulletCategoryBitMask
ship.physicsBody?.collisionBitMask = enemyBulletCategoryBitMask
Bullet.physicsBody?.collisionBitMask = enemyCategoryBitMask
enemyBullet.physicsBody?.collisionBitMask = shipCategoryBitMask
enemy.physicsBody?.collisionBitMask = bulletCategoryBitMask

Answer 1

Once you've set a SpriteNode's physics body, you can use the collisionBitMask to specify which other SpriteNodes it will collide with. You'll need to first set each node's physics body's categoryBitMask.
let node1CategoryBitMask = 0x1 << 0
let node2CategoryBitMask = 0x1 << 1
let node3CategoryBitMask = 0x1 << 2
node1.physicsBody.categoryBitMask = node1CategoryBitMask
node2.physicsBody.categoryBitMask = node2CategoryBitMask
node3.physicsBody.categoryBitMask = node3CategoryBitMask
At this point, three of the sprites have their categoryBitMask set. This is what identifies the physics body. Now to set the collisionBitMasks.
node1.collisionBitMask = node2CategoryBitMask
node2.collisionBitMask = node1CategoryBitMask | node3CategoryBitMask
This tells node1 to by collide with node2, but not node3. Node2 will collide with node1 and node3.
Hope this helps.