# Is it possible to find the mass on an object in a simulated game?

Many games (including Angry Birds) use a physics engine called Box2D, which assumes basic Newtonian physics for rigid bodies. In my opinion, it's meaningful to ask whether the physics assumed by the software is such that mass is determinable from trajectories. I have:

1. The acceleration due to gravity of the simulated planet of the game.

2. The velocity, acceleration and displacement of the trajectory (I have the length of the objects inside the game covered).

Even if it isn't possible using these. Is it possible if I managed to find out anything else?

The gravitational force on a body is proportional to its mass $F\propto m$, so the acceleration $a=F/m$ that it produces is independent of the mass. This means that the trajectories of bodies in gravitational fields (without any other forces involved) don't depend on their masses and thus we can't find the latter using any information about the former. So the answer is no.
If you managed to measure the acceleration of the objects due to other kinds of forces you could get more information. If you measure the acceleration $a$ produced by a known force $F$, you can get $m=F/a$. Even if the force is unkown but mass-independent, it is possible to find ratios of masses of bodies as $m_1/m_2=a_2/a_1$ when both are accelerated by the same force.
A force that probably appears in a physics engine is friction, but obtaining information from it can become hard if you don't know how it is modeled. A simple force that might help you and could appear in the engine is that of a spring. It should be $F=kx$, so from the knowlege of $k$ you can use it to determine masses and even if you don't know $k$ you can use it to find ratios as explained above.