J.C.MacSwell

Who is claiming there is none? No one has yet described a set up with no action-reaction pairs, and at least 2 are required for equilibrium if one pair exists. An object, isolated in deep space, can be in equilibrium with no forces acting on it. No one has suggested we contemplate that scenario.

I've heard a libertarian translate JFKs words as "Ask not what those in power can do for you...ask what you can do...for those in power"

I'm pretty certain Ken 's referring to "teach the scum a lesson", being in quotes, was describing the poisonous thought process, not advocating for it.

I have no objection with Newton's third Law. OK. Good. Just giving an example where just because forces are equal but opposite it doesn't constitute an action-reaction pair. So back to your OP... The downward gravitational force is not a contact force...unlike the force between table and book , and they cannot be an action-reaction pair...each must have one of their own, just like you and your twin. So let's look at the actual pairs which Ghideon has just presented: Does this now make sense?

Hi Airbrush. I'm with you as far as seeing the need for better ventilation. I'm less certain that air should be drawn upward as a general case, as I think it could exacerbate some of the problems (such as droplets with virus getting dispersed further rather than heading to the floor), though it could be useful in some circumstances. From an economics standpoint if you double the airflow of a system, you will require 8 times the energy to move the air, as well as double the energy to heat or cool the replacement air to the same temperature. You can change the system to partly mitigate that, but it probably requires extra equipment costs to do so. That said, with the arrival of Covid 19 the economic considerations have changed, as you suggest.

A book, object 'A', on a table, object 'B', exert equal and opposite forces on each other. They are an action-reaction pair. The book stays stationary due to gravitational force of the Earth on the book, which though equal and opposite to the force of the table on the book, isn't an action-reaction pair with it. Let's say you had an identical twin standing on the South Pole, while you stood on the North Pole. Each of you would exert an equal but opposite force on the Earth. This would not be an example of an action-reaction pair.

At what type of temperatures would the strength and stiffness start reducing back toward "normal" and not recover?

I think it was likely more "I will torture this man, under the guise of restraining him, because I am a malicious idiot with no concern or understanding of any consequences"

I don't understand what you are saying here. Gravitational forces always form an action-reaction pair (as do all forces), at least classically. Either can be resisted by a normal force, in whole or in part, except when the normal force is at right angles to the line of action-reaction.

That is the definition of a normal force. Sometimes it is a component of force, say for something sitting on an incline plane, the weight would be counterbalanced by the normal force and the force of friction.

Probably true for the reason you stated, but... ...Isn't that generally true of the forces seen in an FBD? Only the one of the any action-reaction pair, one acting on the free body being of interest, or needing to be considered in the FBD?

Would "forces on two different objects" be more accurate?

Because the fact that the forces are equal but opposite are coincidental...(giving us a static case due to the forces balancing) As already suggested, if the table was accelerating upwards they would not be equal. If the table was frictionless but not perfectly level the forces would not be opposite. But as mentioned all these scenarios only involve forces that have equal but opposite counterparts. Every action having a reaction. For the static case the force the table exerts on the object balances the Earth's gravitational pull on the object... but that is not the equal but opposite force of Newton's third law. The equal but opposite gravitational force on the brick is the brick's equal but opposite gravitational force on the Earth...and the equal but opposite force of the table on the brick is the force of the brick on the table.

Move to Politics?

Except to highlight the difference between unbalanced forces and action/reaction pairs.

Acceleration doesn't change the principle. If something yields to a force, there still is an equal but opposite force. Essentially as Ghideon stated as an additional case.

No, but I can't remember what is assumed, classically.

Residual and balanced lateral stresses aside, it's all net compressive across every horizontal plane, maximum at the bottom of the brick and going to zero at the top.

What makes you think that? Was it a hanging slinky that was dropped?

One thing with regard to the "not a fan" air propulsor...if your set up manages (not necessarily a reasonable assumption but plausible) to put the same energy into the air it will (mostly) do so by increasing the air velocity. If say you reduced the air density to 1/4, the velocity would double...and this doubling of velocity would produce exactly the same lift/drag with 1/4 the air density (assuming the coefficient of lift or drag stayed the same...again not necessarily true...but reasonably possible) With regards to your set up...it makes it harder to help if we don't know what it is but you may have a number of good reasons to prefer not to divulge it on a public forum, or for that matter, to anyone. No explanation needed if you prefer not to tell us or explain why you prefer not to...just helpful to indicate you prefer not to and have reasons. +1

Studiot mentioned torque. So as an example 1 newton acting at right angles to a pivot point or axis one metre away gives you 1 newton metre of torque about that point.

Beside this one? Or am i misinterpreting your request? Well put.

It wasn't clear from the link. I got 5.79 quadrillion US tons based on the Earth being Sea level...and figured the difference was the land volume above sea level. So it seemed about right being that much higher (.29 quadrillion US tons of atmosphere not existing in that volume) But if it's metric or British tons that's about 10% more with no explanation for my being about that much under (that I can readily think of) I know we are now talking mass and I was originally considering weight, but same line of thought.

Was your original answer in metric tons? I assumed it was US tons.