带电粒子

一个带电荷的零尺寸粒子。他有一个唯一的名称，以及五个参数：

- position: The X/Y position of the particle, relative to the center of the world.
- velocity: the velocity of the particle. Unit: meters/second.
- force: the force with which the particle is moving around.
- mass: the mass of the particle. This influences forces with which the particle interacts with other items.
- charge: The amount of positive or negative electricity deposited on the particle. Unit: Coulomb.