Swingers revisited

This is one of my weirder little fantasies. Sorry to go on about it, but when I'm on a swing (which I often am, a) because I like it and b) I have a child who's still young enough to like it, so I have a valid excuse) I always think spanky things.
Not sure why. I think it's about the way your bottom sticks out in a distinctly inviting way why you really get going on a swing.
It seems to me that anyone with even a hint of the spanko about them who's standing behind me must have an inclination to smack. There (in my case) is one curvy and rather big bottom hurtling at them that is just begging for a good, meaty spank.
If roles were reversed I don't think I could resist. Anyway, I happened upon this image today and that got me thinking about the swing-spanking equation again. In this case the position isn't quite right but the basics are there: 

Swing + Instrument of Correction = Ouch 

It don't mean a thing...

...if it ain't got that sting. I'm not very good on physics. I just didn't bother to listen in class. A generation or two earlier I'd have been obliged to listen - or take a caning.

But that wasn't on the cards for me, so I didn't listen. So I failed my exam and I still don't understand much. If I had I'd be able to answer my 'spanked on a swing' conundrum.

I'm swinging backwards and at the very same moment a palm, or some other spanking implement, is swinging forward. When one and the other collide do butt and implement meet up with twice the force?

It's occured to me when I am on a swing - as I was this morning - that my bottom sticks out in a rather inviting way. Does that sound conceited? Sorry, but I'm pretty sure that inviting is the word.

 If I could clone myself (I wasn't bad at Biology - I got a B) then the me watching would feel an over-powering urge to whack the rrather cruvy, big behind of the me on the swing as it hurtled back towards me. Too tempting.

 And that swing-assisted spank would smart a great deal more than just a regular, everyday one, wouldn't it?If there's an ologist out there I'd be grateful for a definitve answer.

Sadly, I can't think of a way of experimenting with the forces involved. It has to be some sort of offence for adults to play spanking games on a public park's children's play equipment, hasn't it? And we don't have a tree in the garden big enough to hang a swing on. So it will have to remain a bit fantasy, a bit physics problem.