Gravity is what keeps you on the ground or flying up in a level. Gravity is normally at 1.00 but it can be more or less. Higher gravity makes you not able to jump high or not able to jump at all and reach max falling speed faster (you cannot go faster than your max falling speed no matter what gravity). Less gravity makes you jump higher and reach max falling speed slower. Having negative gravity will make you fly up not giving you a choice whether you want but if you have -.72 gravity or more you can go down by holding the down key, if you have -.73 gravity or less you cannot go down but holding down will slow your rising speed. If you have negative gravity have great care not to fall off the top of the screen since you will not respawn as if you fall off the bottom of the screen but you will keep on speeding upwards so it is recommended to forfiet when you are in this kind of situation.