Okay, so I'm making a platformer, and I wanna know how I can make a arc'd jump easily. Like what Mario does in super Mario Bros 1. Any ideas on a simple way to accomplish this?
Interesting question; having taken Physics classes, I take this sort of thing for granted, when really it is an intriguing idea.
The key point is that X and Y movements are distinct from each other. An object in motion will sustain its X motion, and its Y motion will be affected by gravity at a rate which you set.
You should track the sprite's X and Y velocities. When standing still, the sprite has an X velocity of 0; when moving, it has a constant velocity. When touching the ground, the sprite has a Y velocity of 0. When the jump button is pressed, give the sprite a Y velocity.
Now every frame, reduce the Y velocity by some amount; this is your gravity magnitude. But if the sprite is touching ground, set the Y velocity to 0 so that the sprite doesn't move into the ground. And then modify the sprite's position by (velocity*time).
Here is a decent-looking Physics lesson which demonstrates these separated velocity components: http://www.physicsclassroom.com/class/vectors/u3l2c.cfm
If this was not the answer you're looking for, and you actually mean something more complicated by an "arc'd jumping method", then please elaborate!