A New Theory for Systems That Defy Newton’s Third Law

Re:A New Theory for Systems That Defy Newton’s Third Law by bodhiandphysics on Friday November 12, 2021 @07:46PM (#29206279)

Newton’s third law is just the conservation of momentum... and lots of interesting systems don’t conserve momentum!

[ Parent | on HN ]

Re:A New Theory for Systems That Defy Newton’s Third Law by nextaccountic on Saturday November 13, 2021 @08:12AM (#29209487)

But closed systems?

[ Parent | on HN ]

Re:A New Theory for Systems That Defy Newton’s Third Law by bodhiandphysics on Saturday November 13, 2021 @08:17PM (#29214697)

Sure! A ball in a box is a closed system the doesn’t conserve momentum.

[ Parent | on HN ]

Re:A New Theory for Systems That Defy Newton’s Third Law by nextaccountic on Saturday November 13, 2021 @11:57PM (#29215431)

How so?

Consider that the evolution of the system will be the same regardless of where the box is located, and as such the system has translational invariance. Per Noether's theorem it must conserve linear momentum.

[ Parent | on HN ]

Re:A New Theory for Systems That Defy Newton’s Third Law by bodhiandphysics on Sunday November 14, 2021 @06:17PM (#29221709)

I meant the infinitely massive box of physicists dreams. Translational symmetry is broken by the boundaries of the world

[ Parent | on HN ]

Re:A New Theory for Systems That Defy Newton’s Third Law by nextaccountic on Monday November 15, 2021 @04:27AM (#29225446)

You mean, a box that is immovable because it has infinite mass?

Hmmm I don't get it. What boundaries, the box boundaries? How does it break translational symmetry?

Anyway in this case I think at least elastic collisions will still conserve momentum, eg this https://en.wikipedia.org/wiki/Elastic_collision#/media/File:... conserves momentum even if the box has infinite mass.

[ Parent | on HN ]