p.setY(y1);
p.setVx((x2 - x1) / stt.getTimeStep());
p.setVy((y2 - y1) / stt.getTimeStep());
p.setMass(1);
p.setCharge(charge);
stt.addParticle(p);
Simulation s = new Simulation(stt);
s.prepareAllParticles();
// The simulation always creates its own copy of particles