Terminology for levels of body interactivity

[Martijn]

I have two simple questions:

1) What is the scientific term for "a body that cannot affect another body"?
Effectively, as if this body has a mass of zero. The body can move freely until it contacts another body, in which case it will not be able to affect the other body in any way, and thus be deflected.

And conversely:

2) What is the scientific term for "a body that cannot be affected by another body"?
Effectively, as if this body has infinite mass. The body can move freely, interactions with other bodies cannot effect this body in any way.

This all within the context of body interaction (such as collisions), specifically rigid body dynamics and forward kinematics.

I'm not actually sure there are commonly used terms for these, in which case you are free to suggest something.

 

[Drakkith]

I've never heard of what you are talking about. As far as I know everything interacts with everything else. The only thing i can think of, is perhaps dark matter, which only interacts gravitationally as far as we know. But I don't think that fits your definitions.

 

[Martijn]

Well, it is purely a theoretical concept, one that violates the laws of physics. But in the same way that an structural engineer ignores the gravitational pull of Jupiter, as the force is negligible for all practical purposes. So when I say a "mass of zero", I mean that the mass is negligible in the interactions and therefor ignored.

Anyway, what I am most interested in is finding an appropriate name for these types of bodies.

 

[Drakkith]

Ah I see. I wish i could help you with that, sorry.

 

[Martijn]

*bump* (of negligible force)

Anyone else maybe?