AddForceAtPosition Confusion

Hello,

I am having a hard time understanding the results of a Rigidbody2D's call to AddForceAtPosition with varying position input. It's resulting sum of momentums (linear and rotational) depend on the given positional offset.

No matter the given offset position, the body simply experiences a velocity change akin to an AddForce call (always gets this linear momentum delta).
If a lever is formed by the given position to the body's center of mass, the body then *additionally* experiences a rotational velocity change akin to an AddTorque call (only angular momentum delta is variable).

Shouldn't a body's call to AddForceAtPosition result in the same sum of change of linear momentum and angular momentum?
I would assume the greater the lever, the more force is "dedicated" to applied torque, and so the body's velocity delta is reduced, but currently torque is supplementary, instead of being accommodated for.

This is most probably expected behavior, but why? Isn't it physically inconsistent?

I see AddForceAtPosition as an inelastic collision between the body and an infinitely small object going really fast. Is my understanding of physics even correct?


Note that the script uses ForceMode2D.Impulse, however Force mode does the same.

Cheers

 

Surprisingly, the result is physically correct. The force acts over a longer path in the second case than in the first. As a result, the force does more work and applies more kinetic energy to the cube.

This paper explains this effect in the section 5.5 (page D28): https://www.cs.cmu.edu/~baraff/sigcourse/notesd1.pdf

Here's the relevant part:

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A practical example is the pool balls. Hitting the ball off-center gives it a spin additional to the actual linear impulse, which is the same regardless the hit point.

 

Very interesting, thank you for a clear and sourced answer. I don't understand it fully just yet, but it's good to know I'm wrong. So, the short answer is, the greater the lever, the more the force can be 'absorbed' by the body?

Your pool ball example is still confusing to imagine because off-center collisions result in a different trajectory, but I'll just assume the cue ball is launched at the same speed, and the target ball is sent off with consistent resulting speeds (albiet with varying rotation )

 

The greater the lever, the more distance is traveled by the force. Force over distance = work = energy. Therefore, the same force "transmits" an additional energy to the body in the form of angular velocity.

I meant when hitting the cue ball with the cue stick. The cue ball is sent off with the same speed and direction regardless being hit off-center or not.