code: public void setSpeed(float speed) {
  		float currentSpeed = (float) Math.sqrt((velx*velx) + (vely*vely));
  		velx *= speed;
  		vely *= speed;
  		velx /= currentSpeed;
  		vely /= currentSpeed;
  	}
docs: Set the current speed of this particle
  
  @param speed The speed of this particle