Augmented Reality Physics?

I was checking out the AR started Kit project, it displays a box on top of a Hiro marker. I downloaded a Hiro marker on my phone and used the camera on my laptop to view the results. Sure enough, it displayed the marker on top of my phone.

I thought it would be cool if we could move the box around the screen using keyboard controls like you would be able to in a non-AR setup. I managed to get forward/backwards working using translations:


But I want to use physics to move the object on screen using forces/impulses. I tried to set a collision and rigidbody on the entity in the project but errors are given such as

Cannot read property 'applyForce' of undefined

Gravity is also a problem. Here is the project:

If anyone has any suggestions for applying forces, let me know!