Define friction getter and setter just once, instead of for each entity instance.
Fix bad scope referencing.
Define .bounciness getter and setter once, instead of for each entity instance.
Define .angle getter and setter once, instead of for each entity instance.
Define .isBullet getter and setter just once, instead of for each entity instance.
Define vel.x and vel.y getter and setter once, instead of for each entity instance.
Simplify code by using 'this' instead of a variable that points to 'this'.