swansont

Or, to put studiot's physical science example another way, it's saying that the system is large enough that the small changes are outside of any experimental determination, while acknowledging that using "infinite" is unphysical.

This is a been a problem with your posts - you either don't read what was said, or comprehension isn't there. So you respond to something other than what was claimed Like here. I did not make a general claim about objects, I made a specific claim that the derrick is an object. That in no way can be (validly) extrapolated to mean that other systems can’t be comprised of multiple objects. So bringing up the fact that you can stack two books doesn't have any bearing on this. The can't form an action/reaction pair, since they don't satisfy the criteria for action/reaction pairs. Since you refuse to go look this up (and somehow you are arguing about Newton's third law without knowing this), I will once again list them. Make note, since I won't do it again. The criteria are: 1. Equal in magnitude 2. Opposite in direction 3. Act on different objects (they act on each other) 4. Same kind of force ALL criteria must be met. Normal force and gravity fail to meet 3 and 4, thus, any student of physics hoping to demonstrate understanding of the concept must realize that these are not an action/reaction pair. And, as I said, there are no reaction forces present, since a reaction force is one exerted BY the object. All of the forces in the diagram are exerted ON the object. The example in question was the bat and the ball. It doesn't apply to that pair of forces, since they are not an action/reaction pair. If they were identical they would be in the same direction, and identifying an action/reaction pair does not tell you whether or not there is a net force. See above. I can't believe you are this effing lazy. Newton's laws are fundamental to dynamics, too. Lots of problems are solved where F ≠ 0. You use the second law for them too. But it's pretty obvious you haven't studied more advanced physics if you have the misunderstandings you do. Not a strawman as you actually did it. Equilibrium is a conclusion from the second law. Action/reaction is the third law. They are different concepts. Did Dr. Czerski write that article? I didn't find her name on the first page, or on page 5 It really hasn't come into question when I talk about work, which is a tad more advanced than lecture 2 of physics 101. I realized that the problem is your interpretation of the website, and the issue is less of one of qualification as in clearly explaining the concepts. You can't ask a website for clarification. I didn't dismiss their claim. I inquired why YOU dismissing mine in favor of theirs. AFTER I pointed out that they did not actually back up your claim. (a can vs. must issue you have asserted didn't happen, and yet, there it is) If it's all fine then how about applying that information? The book and desk example mentioned gravity. Gravity in this kind of problem is exerted by the earth or some other (typically very large) mass. Thus, it can't be ignored. But, once again looking at the above list of criteria for action/reaction, we see that these force fail to fulfill all of the criteria. In that kind of problem you are worried about the moment of impact, though it would depend on the specific question. But in all the time the ball is in contact with the bat, the single FBD would apply, since those are the forces present. They may change magnitude, but that doesn't negate a FBD that is just identifying the forces Energy and momentum are not things that appear in the FBD. Forces only.

You have cause and effect mixed up here, and also are making some implicit assumptions about what variables are fixed and what can vary Yes, if you reduce temperature, if the volume decreases, density will increase. But if volume is held constant, that would not be the case. Pressure would drop (PV = nRT, in cases where you can assume an ideal gas) But that's not what happened in the early universe, as others have explained

I'm unfamiliar with the explanation and can't recite it off the top of my head, but I'm sure it doesn't involve the variation of physical constants. If you don't have a model to present, then your thread does not meet the level of rigor we require. A superconductor is not a vacuum, so I'm not sure of the relevance? Instead of bringing up other phenomena, you should have focused on your speculation. Since you don't have a model, this is closed. If you have questions about anything you've brought up, feel free to ask, but if you have pronouncements about anything, you need to back it up.

! Moderator Note This constitutes advertising, which we do not support. This looks like speculation, so it has been moved. Let's have the actual model. Which, of course, your model will show... There's magnetic permeability, but that's a constant, so it won't have a gradient. So the ions are only at the surface? Why are these dipoles attracted inward?

This points out the two different situations we've encountered. One is Newton's second law: F = ma. The acceleration of an object (which may* be zero) depends on the net force acting on it. So you identify and add all the forces acting on it together. Usually highlighted by a free-body diagram (FBD). The other is Newton's third law. This identifies pairs of forces - each pair consisting of one exerted by the object, the other exerted on the object. (The is no FBD, because a FBD only includes forces exerted on the object). These pairs are equal in magnitude and opposite in direction, as well as being the same type of force. Neither case requires that the net force be zero. Resolving a FBD will tell you if there is a net force. Identifying action-reaction pairs will not (though if there is only one pair you can deduce that there is) *may be zero does not mean must be zero. Zero is a possibility, but not a requirement.

Library.

That’s for you to investigate. The Wikipedia article has a reference

Either the derrick is an object or it isn’t. You can’t have it both ways in the same sentence. Only forces (and torques) acting on the derrick are shown. No reaction forces are depicted in that diagram. Orthogonal forces cannot negate each other. If you don’t understand that, you need to open a new thread to clear up your misconception There are two forces. You use “they” when there’s more than one of something. They - the two forces - are not an action-reaction pair. It’s not a situation where Newton’s 3rd law tells you anything. Opposite directIon, and acting on different objects, means they are not the same. Not identical. Go back and read the thread Where did Newton say that his laws only applies to statics? How do you use the 2nd law, if you are limited to statics You did more than imply it, you literally said it. And where you saiid itx you mistake zero net force to mean action-reaction. They aren’t the same thing. So all the times I was teaching physics I was actually reporting? 1. Prove it. 2. You haven’t understood my objection, which really is to your (lack of) understanding of what the site said.

Yes. It has to do with vacuum states having zero-point energy. You aren’t deriving the value from any physics. You’re just manipulating constants to get a number. Why not multiply the energy by the fine structure constant, raised to the ~60th power? It’s unitless, so you’ll still have units of energy. Then the problem goes away. The number might be. But the QED example comes from QED, not manipulating physical constants. Where is the QED analysis?

I didn’t say you made a numerical error Yes. Have you read those pages? They talk about the Casimir effect and a particle in a box zero-point energy. You know what those links don’t have? Planck units. What is your physical justification for these calculations? (i.e. something in physics, not derived from Planck units) What phenomenon has such a frequency? (i.e. something in physics, not derived from Planck units)

If you define “at rest” to mean v=0. So why not just say v=0? It avoids the ambiguity of language. What kind of diagram do you need? It’s a ball that is momentarily not moving. There’s a downward force on it.

“However, in both quantum electrodynamics (QED) and stochastic electrodynamics (SED), consistency with the principle of Lorentz covariance and with the magnitude of the Planck constant suggest a much larger value of 10^113 joules per cubic “ My point is that you do not appear to be using electrodynamics. You are using Planck units, without making the connection to QED or SED. Planck units predate both GR and QM, so it’s dubious make too strong of a connection to them. For example: “The Planck time is the unique combination of the gravitational constant G, the relativity constant c, and the quantum constant h, to produce a constant with units of time.” https://www.universetoday.com/79418/planck-time/ Combining constants to get units right is not something you can take as physically meaningful. When talking about a factor of 10^122, a missing factor of pi is not a big deal.

People are not removing statues because they were built by slaves. Many of the confederate statues in question were erected much later, with the express purpose of spreading misinformation about the civil war. Rewriting history. It’s ironic to think tearing them down is rewriting history.

A third thing is how did the importance of education appear as the criterion by which this should be measured?

The problem I see is that Planck units are a unit system https://en.wikipedia.org/wiki/Planck_units#Definition “the system is internally coherent. For example, the gravitational attractive force of two bodies of 1 Planck mass each, set apart by 1 Planck length is 1 coherent Planck unit of force. Likewise, the distance traveled by light during 1 Planck time is 1 Planck length.” Notice how it’s not referencing any actual particles, or measured phenomena I don’t understand why anyone is ascribing more significance. It doesn't seem to justified anywhere. You can do your exercise with other units. The SI energy density is 1 Joule/m^3.The cgs energy density is 1 erg/cm^3, which is not the same - the differ by a factor of 10. That’s OK, though, because there’s no physical significance here. I have seen reference to the vacuum energy calculation from the Casimir effect, and from a particle in a box. Those have QM significance.

<looks at thread title. looks at OP. sees no contradiction with statement> Thank you for agreeing with me, that this thread was about civil war statues. Makes your “no” confusing, though. You later made a comparison of British action with reading found in US school curriculum and deemed the analogy apt. I disagree, because if I go through towns/cities I’m not confronted by works of literary fiction in the town square. I think we’re caught up.

Marines and Navy banning them from spaces under their control.

“No net force” is a concept that can only apply to one object. It has no bearing on action-reaction These forces are horizontal, and can’t “negate” gravity. They can’t. I said they weren’t a third law pair. So asking me how they can be is...odd. Are they the same? The force the ball exerts on the bat is being exerted on the ball? How does that happen? There are. They’ve been discussed about a bazillion times. Are you not paying attention? Why are you assuming statics? can ≠ must physics is not reporting. No. I said nothing like that. I don’t think a lack of expertise is dishonesty. I don’t think you’re being dishonest by misunderstanding this. Why would you go there?

The topic here was civil war statues, meaning they were traitors and they lost their war. I don’t see that drawing the line at traitors to be a difficult decision. It’s fiction, and does not represent a government endorsement of slavery/subjugation/mistreatment of anyone. It’s apple vs oranges Also, people are not entitled to have their statues displayed on public property. What books are assigned as reading is up to teachers, in the furtherance of the education of children

The video depicts a finite number of elements of a finite height. It says that a dimension is small, “almost zero small” which is wrong I don’t see why “infinte” should be mentioned at all. Don’t subject yourself to this video any further. Someone else on youtube must have done a better job.

Yes, the use of the phrase there is bogus. It’s not a very good video, in many ways.

Where in the video, or alternatively, provide a transcript. From the first ten seconds, though, I was not impressed, so it may be that there’s just no real credibility here.

That does not follow. Planck units are not a QM prediction.

Way to miss the point. If they are not an action-reaction pair, Newton’s 3rd law does not apply. They don’t have to be equal in magnitude, opposite in direction, or the same type of force. In that example, they happen to be equal and opposite, because the point of such an example is to make you apply your knowledge. The ball hits the bat, the bat hits the ball. The forces are not on the same object. They are an action-reaction pair. The contact force and gravity, the two forces acting on the ball, are not an action-reaction pair. Still no. The force an be unknown or not accounted for. You can be in a rotating frame of reference. Those circumstances will not change the action-reaction relationship of other forces that are present. CAN be. Not MUST be, or CAN ONLY be. And perhaps consider that a BBC website might be a less trustworthy source than someone with a PhD in physics. Again, it can’t. And again, what Newton’s laws tell you is that if you are in an accelerated frame, then whatever pseudoforce you identify will not have an action reaction pair.