applyBehaviour(particle, time, index) {
    this.calculate(particle, time, index);
    particle.a.add(this.force);
  }
Apply this behaviour for all particles every time

@method applyBehaviour
@memberof Proton#Proton.Force
@instance

@param {Proton.Particle} particle
@param {Number} the integrate time 1/ms
@param {Int} the particle index