# What is the scientific definition of a force?

Discussion in 'Physics & Math' started by Magical Realist, Mar 22, 2022.

1. ### arfa branecall me arfValued Senior Member

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In physics you deal with units. However you decide or choose which conditions you include in your theory, if you can't "recover" the physics--an actual path "s" through space, over a finite interval of time "t", there is no hope. If you "abstract away" the mass, or anything physical for some reason (why it would be or who to, are different problems), then you have to put it back to recover observational results.

In vector spaces unit vectors can replace any basis set of vectors, in that space. Force and momentum are both vectors, but are not in the same vector space(s).
In mechanics of rigid bodies in motion, mass is distributed into a volume with a shape.

One of the curious things about the moment of inertia I, is that it's related to a fixed (by the geometry and a chosen axis of rotation), radius, the radius of gyration. This is another of those geometric things about the gravitational/inertial interactions.

The radius, call it a thing defined at a boundary, a geometric condition or constraint. has a number of small volume elements somewhere along it; the problem of finding these two geometric conditions--I and the radius of gyration--is a calculus problem, finding the volume of revolution. Unless you don't have a nice ring or flat disc, you have to get geometric another way. Finding the radius of gyration gives you the moment of inertia because of a geometric relation. The mass of a rigid body with an homogenous density of matter is fixed for any small volume element you sum over.

But you need to have this mass-density relation, calculus otherwise will let you deal with a small ring as if it's a 1-torus with a lineal mass density. You recover observable physics by finding the inertial moments along this abstract 1-torus or "thin" ring. So a disc is a sum of small, concentric rings, so I for a ring is basic, or a foundation for the next composite shape, or distribution of matter, the disc, which is topologically equivalent to a bowl, which is . . .

3. ### Motor DaddyValued Senior Member

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F=ma is a NET force. If acceleration is zero then force=zero.

So I push on a brick wall and it doesn't change velocity, which means the acceleration is zero. You're trying to tell me the force=0 because the acceleration is zero?? The NET force is zero, but I am applying a force to the wall, and it is not accelerating.

James, are you still having difficulty coming to terms with what force is?

Do you need me to school you some more? You miss me don't you? Admit it!

5. ### James RJust this guy, you know?Staff Member

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Perhaps you didn't understand it.
Yes.
So is oversimplification. Right?
My post was concise.

7. ### James RJust this guy, you know?Staff Member

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If acceleration is zero, then net force is zero.
Yes, but you're not the only thing applying force to the wall. Traditionally, walls are attached to the ground, for instance.
What do you mean "still"? It sounds to me like you're a bit confused about what "net force" means.
Who are you?

8. ### Motor DaddyValued Senior Member

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Right, the NET force is zero. Do you know what NET is? In a tug of war, the net force is zero when neither side is moving, but each applying 1,000 lbs of force to the rope in opposite directions. Zero net force, and zero acceleration. But the rope could break!

So you think the wall is applying a force to me? I am applying motion to the wall, and the wall is resisting my motion, which creates force. Force is created by a resistance to motion. The wall is not applying a force to me, it is a resistance to my motion.

You never mentioned net until I mentioned it. F=ma is a NET FORCE, and you know what net means, right?

The creator of MD's Box! Duh?

9. ### James RJust this guy, you know?Staff Member

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Yes. The net force on an object is the vector sum of all of the forces acting on that object.
It sounds like you're considering the two teams and the rope as if it were a single object. In that case, what you say is fine, as long as we understand that we're talking about the net external force on the system (zero in your example, where there is no acceleration). In this picture, forces on the rope are internal forces. The rope is only able to withstand a certain tension force. If that is exceeded, it will certainly break.
Yes. Newton's 3rd law: for every action there is an equal an opposite reaction on some other object. You push on the wall; the wall pushes back on you with an equal force in the opposite direction. If that force wasn't there, you'd fall through the wall.
Motion is the result of a force, not the cause of it.
Hmmm.... maybe.

F=ma. The "m" in that equation is a measure of the inertia (resistance to motion) that the system/object has. To accelerate the object, a (net) force must be applied. The resulting acceleration will be directly proportional to the force and inversely proportional to the mass (inertia).
Yes it is. Newton's 3rd law. See above.
Yes. See above.

Last seen at sciforums in 2014. You asked to be permanently banned, I believe (?) I wasn't the one who handled your request.

How are things? Why return now?

10. ### Motor DaddyValued Senior Member

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Things are about par for the course. Being retired I do what I want, and have all the time in the world.

I still visit this place just about every day, mainly to get a laugh, but to learn a thing or two here and there. Not much good content here for the past decade.

I couldn't control myself when I saw Neddy Bate's comment about me. I always liked Neddy, we had some good debates and he taught me a lot.

So I figured I would drop in and say hi. Plus I had to rattle your cage a little. Good times!

11. ### James RJust this guy, you know?Staff Member

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That's a surprise. How have you managed to resist the temptation to post anything for 8 years?

12. ### Motor DaddyValued Senior Member

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I have a strong mind. I quit smoking cold turkey after a pack a day for 26 years. I just made up my mind I was not gonna smoke any more, and that was that. Never looked back.

I figured with this place it was worth getting banned again to say hi to Neddy.

James, you should go to https://ilovephilosophy.com/ and debate me on some stuff.

Maybe you are already there? From time to time I get a "James R." vibe from different people. There is one there now that seems to be just like you. I won't mention any names.

Last edited by a moderator: Apr 25, 2022
13. ### James RJust this guy, you know?Staff Member

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Well, you're here for now, anyway. Didn't you ask to be banned, previously?
I'm not there and have not been there. Just so we're clear. If there are any fanboy impersonators, I'd love to know. Flattering!

14. ### Motor DaddyValued Senior Member

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Yes, I asked to be banned permanently because I was sick and tired of being temporarily banned for petty BS just to shut me up. Every time I turned around I was getting banned for some stupid petty BS, so I just requested a permaban, and it was granted. It was obvious I was not welcome here, so I left! How's the place been since then? Everyone leave? This place was rockin' with AN, Farsight, Neddy, rpenner, and tons of other people. It's dead now!

15. ### James RJust this guy, you know?Staff Member

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Fair enough. If the vibe of the place doesn't suit you, for whatever reason (including how moderation is done), then it makes good sense to leave. I congratulate you, since so many other people seem to have huge struggles with that particular idea.
Membership has dropped off quite a bit, I think - talking about active members here. Probably they are all on social media, or having lives or something. [Ha! You can have your so-called "lives", you dirty rats! We'll see who is laughing when the apocalypse comes! Bwhahaha! ..... ahem. Excuse me. I don't know what came over me.]

16. ### Michael 345New year. PRESENT is 72 years oldlValued Senior Member

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My life was great

Had great female company in Bali

Extremely fortunate being with the girl I was with when I became stranded (ended up being for 18 months)

Appointed herself myself sponsor, guided me though Indonesian rules and regulations

Even after a ton of paperwork obtained for me first vaccinate against COVID-19 which was accepted ligit when I got back Australia

Now trying to get back to be her sponsor to come Australia

17. ### Motor DaddyValued Senior Member

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Are you the one posting "Jesus is coming" signs on the side of the road?

18. ### MrOrlockRegistered Member

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A true force requires a field particle mediator. Gravity Interestingly doesn't have one from first principles of it being a pseudoforce in GR. So gravity isn't exactly a force per se, which would answer why we can't unify it like a quantum field.

Semi classical gravity all the way!

19. ### DicartRegistered Senior Member

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Yes, historicaly, but you can understand it more generaly as : The "thing" that can (will) change something.
A force is not only associated with motion but can even be associated with "breaking" (changing) something.
Force is what physicists refer to, as soon as they observe a change : It is the technical term of this manifestation of the real.

20. ### James RJust this guy, you know?Staff Member

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This is nonsense.

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22. ### James RJust this guy, you know?Staff Member

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I did not same "the same" as you. The exact words make a difference. In this case, they are what makes my explanation correct and yours nonsense.

I did not say that force is a "technical term of [a] manifestation of the real" or anything like that, or imply that force is always implied with any change. Those were your words.

23. ### DicartRegistered Senior Member

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Try again with fewer words so we can compare our definitions.