I am making a game that involves spaceships and I was building an engine block. That engine block spawns a "thruster fire" under it that represents the...thruster fire.

My question revolves around the physics engine that my editor uses. You don't need to know anything about it except that it simulates 2D physics.

If I apply a force to propel the ship from the engine block, it behaves a certain way. But if I apply the force on the "thruster fire" block, the pivot changes and the ship flies in a slight but different angle.

In which block would it make more sense / be more realistic to apply the thruster force? I have barely any physics knowledge to decide myself. A short argument to why said answer for others that might stumble here would be appreciated.

I don't know how relevant it is, but its in space. No gravity or air friction involved. There is no structure stress within the ship due to the force being applied in peripheric parts of it. Its for a game :)


1 Answer 1


The thrust coming from a rocket engine is exerted on the engine bell, and it is directed along its axis of symmetry. It's not completely clear how you're modelling your ship but it is probably more realistic to apply the force to the "thruster fire" block, whatever that is.

It's important to note, though, that if applying the force to the engine bell and the engine block produces different effects, then you are likely to be neglecting important rotational dynamics. Are the two points collinear with the axis of the engine? Are they collinear with the centre of mass? In particular, if you have a rigid body and you apply a force whose line of action does not pass through the centre of mass of the body, then it will exert a torque on it, and will therefore tend to rotate the body as well as translate it. If you're looking to make your game more realistic, I would start with those effects, to be honest.

  • $\begingroup$ Thank you! I can also apply the force in a point exactly between the two blocks. When I link the blocks of the ship, it behaves like a single solid entity, and the force is applied to the area of the thruster block. Yes it does spin the ship, and it is normal to do so from what I gather. $\endgroup$
    – Discipol
    May 10, 2015 at 7:09

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