Hey Danyel!
I assume the speaker of this sentence is trying to be funny in his delivery to avoid embarrassment, as falling down and tripping over is generally considered an embarrassing act.
A gravity check would involve trying to experiment and seeing what happens when you fall (on purpose).
Doing a ‘gravity check’ is less embarrassing than tripping, and it can even be impressive, think about Newton and his work with gravity!
His intention here is to show that tripping is not embarrassing for him, because he’s doing it on ‘purpose’. Instead of accidentally tripping, he is doing it for a specific reason (in this case, checking gravity).
Of course, he’s not literally doing a ‘gravity check’, it’s more a humorous metaphor to avoid any embarrassment he might feel from the act of tripping. This is at least my perception of this sentence!
Hope this helped in some way. Happy learning :)