if (keys.up && !keys.down) {
    acceleration.add(0,0.001);
    velocity.add(acceleration);
    location.add(velocity);
    showDebugInfo();
}

if (keys.down && !keys.up) {
    acceleration.add(0,-0.001);
    velocity.add(acceleration);
    location.add(velocity);
    showDebugInfo();
}