The Hulk vs Thor fight is one of the MCU's greatest scenes. It's funny, entertaining and shows how powerful the two are. But did you know that the punch wasn't meant to kill Thor?
As it turns out, the writers of the film wanted to show how much stronger the Hulk was by showing him curb-stomping the other title character. They were also trying to show how the gamma radiation in Banner's blood caused his mutation.
To do this, they had to make the Hulk stronger than any other incarnation before. This was accomplished by giving the Hulk a fusion reactor in his chest that made him more gamma-fueled than ever before. This increased his strength, speed and ability to heal.
During the battle in the woods, Hulk ripped Ironman's armor to shreds. This was a clear indication that he wasn't holding back. Hela then asks if he's bloodlusted and he says yes.
Hela then explains that she has half a soul and wants the other half from Thor. He assures her that he won't give it up without a fight, which she agrees to.
They then go back to Asgard where Loki isn't all that happy to see the mighty Hulk. Hela convinces him to bring the beast to her realm, but he says he'll subdue him with lightning and his fists before bringing him down.
So why didn't he just do that? Because the momentum principle says that if you have equal force acting on an object, then it must be balanced out. So if Thor pushes on the Hulk, the Hulk will push back with an equal force in the opposite direction. This will change the momentum of both characters and pull them down.
