A speed ball increases speed of your bow string because once the ball starts moving momentum is created and the ball aids in pulling the string to the resting position.

Howevr, you can't just place one of these speed balls anywhere on the string. There is a "sweet spot" close to the cam(s) where it will have a positive effect. No two bows are the same when it comes to this spot so you must experiment with its placement and a chronograph to achieve the best results.

Normal accessories such as peeps, nocks, and string silencers slow the bow down due to them being more to the center of the string and there fore are added weight that the string must pull foward just like an arrow.