office argument to be settled:
is there any action that can be made that doesnt cause a reaction?
if i sit in my chair doing nothing, and i consider it my action to be doing nothing, there is no reaction to this as far as im concerned.
my friend here thinks otherwise.
aside from this, any physical or chemical action is fair game. can this be proved true?
The phrase ‘for every action there is an equal and opposite reaction’ is sorely abused and has been watered down to mean something like ‘everything has an opposite’.
Sitting in a chair doing nothing is (at least in theory) not an action at all, but hang on, yes it is - your arse is pressing down on the chair(action) and the chair is pressing up on your arse with exactly the same force(reaction).
Actually I’m not sure if that isn’t itself an abuse of the term.
Try sitting on your arse when it’s your turn to buy a round. Tell me if there’s a reaction.
If you sit in your chair, you are exerting a force on the chair - due to your weight. Now do you fall down? No. Do you spontaneously, without a conscous effort on your part, suddenly spring out of the chair? No. This is because the chair is exerting an equal and opposite force, a reaction, on you, to keep your arse on the chair, in equilbrium.
The concept of action and reaction is valid in physical and chemical systems, and is a direct consequence of the laws of conservation of energy and momentum. No physical change to one object in a system (e.g. you and the chair) can occur without causing a corresponding physical change to another object in a system.
so the answers no then? there must be some action i can take, physically, that wouldnt cause a reaction, such as in a vacuum. or space.
Why must there be?
Let us know if you do find such an action because it will revolutionise space travel - the reactionless drive is very useful, but currently only exists in works of fiction.
There is not. Unless you fancy trying to find a way to create energy from nothing,. which is physically impossible.
Why do you think there must be some action in a vacuum or in space that will allow you do act on something without there being a reaction?
If you consider doing nothing an action, then you should consider doing nothing an equally valid reaction.
A common misconception. Even if you had hydraulic pistons in your buttocks which allowed you to jump out of the seat, or if you break the chair and fall through it, the force of chair on buttocks is always equal in magnitude and opposite in direction to the force of buttocks on chair. The Third Law is not just for inertial systems, or systems in equilibrium, it’s for everything. It also happens that the upward force of chair on you is equal in magnitude to the downward gravitational force of the Earth on you (this is what’s called weight), but that’s not the Third Law, it’s a special case of the Second Law, which is only applicable because your example happens to not be accelerating.
I don’t think it’s helpful, by the way, to try to explain “why” the Third Law is true. It’s a fundamental fact of physics, just because that’s the way the Universe is. You can consider it as being equivalent to the conservation of momentum, and therefore can call conservation of momentum fundamental and use that to derive the Third Law, but it’s more typically done the other way around.
Thank you Chronos. That is what I meant to say, but I couldn’t quite articulate it. And I *should[/I, being a physicist, know better.
Exactly what I was going to say. The beauty of it is that it should satisfy the physics-challenged officemates of the OP.