When a woman is being double penetrated and the 2 mens balls clash together, like a set of Newtons balls.
Dude, i was totaly like doin a chick last night and i swear there was some Newton's balls action going on, it was freaky!
Originally an experiment demonstrating the principle of conservation of momentum, Newton's balls are five metal balls suspended in line by fine wire or string. When one ball impacts the rest, momentum is conserved and the ball at the other end is knocked into the air.
Alternatively, Newton's balls can be used to describe a sexual situation. When two men engage in anal sex in the doggy style position their balls slap together, creating an effect much like that described above. Gay people often feel that such a situation is baroque.
"Bastian and Gabe got the Newton's Balls effect happening last night, I could hear it from next door!"