exchemist

When you jump in the air, you use your muscles. There are connected only to your bones, i.e. they act purely internally. How do you account for your ability to jump in the air?

This is now so garbled as to be impossible to tease apart and correct. Almost every word is wrong or meaningless in the context in which it appears. Are you now really now claiming that Newton's laws say the ring can't vibrate, in spite of all the previous explanations?

You are wrong in asserting that " internal forces may not be transferred outside the ring", if the ring is in contact with something external. If you jump up and down on the spot, your muscles exert purely internal forces on the bones of your legs, causing them to extend. If you were not in contact with the ground, nothing would happen. But you are in contact with the ground, so as your legs try to extend they press on the ground and the reactive force from the ground pushes you up. We have already explained why the AC current makes the ring vibrate. What is a vibration? It is a repetitive up and down motion. So exactly analogous to your legs when you jump on the spot. The ring is in contact with the table so every downward motion of the vibration makes the ring jump up in reaction. The motion then changes to an upward one, but the ring is how higher off the table than it was before, so it is free of the table for an instant. There is thus a point in each vibration cycle at which the ring has jumped off the table and is free to move in response to any tiny force. We can get onto that in a minute, but first, do you now understand how a vibrating ring in contact with a table experiences varying forces from it? If you still can't understand this point, we can't move on to the rest of it.

So, let me understand this. The Egyptians, so you say, did not know π, but the pyramids builders who, you say, were Egyptians, did. How does that work? Do you mean that while most of Egyptian society didn't, this hypothetical priestly caste of yours did? Also, you'll have to explain to me why the cutting of the pyramid core into steps precludes them making it 280 cubits high by design.

OK. So, on the right hand side, you know the molar mass. The other thing you need to know is the number of moles of substance, right? How many moles would there be in one litre of the solution, at that concentration?

To put it another way, we know @John2020's (a) is not correct.............because of Newton's laws. @John2020 does not seem to realise they are so well established that the first thing we do in analysing a mechanical system is to apply them and see what they tell us. So the logic is that the ring starts to move, ergo there is an external force responsible. It is then just a matter of identifying how that force arises.

I'm not quite sure what this is about but regarding the effect on g of the Earth's rotation, this once came up elsewhere and I worked out that even at the equator, the reduction in apparent g due to the Earth's rotation was only about 0.3%. It went as follows: - The radius of the Earth is ~4000miles, so its circumference, say at the equator is 2 x π x 4000 which comes to ~25,000miles. - The tangential speed at the equator is therefore 25000miles/day, which is close to 1000mph. - The centripetal acceleration needed to keep an object moving with tangential velocity v, in a circle of radius r, is v²/r. So, for an object at the equator, the apparent centrifugal acceleration it experiences, counter to the acceleration of gravity, will be 1,000,000/4000 = 250 miles/hr². What we need to know is how this acceleration compares with g, the acceleration due to gravity, which is about 10m/sec². To do that, we need to get this result into the same units as g is quoted in:- 1 mile is ~1600m. And 1hr is 3600 seconds. So 250 miles/hr² becomes 250 x 1600/(3600)² = 25 x 16/(360 x 36) = 25 x 4/(360 x 9) = 100/3240 = ~ 0.03 m/sec². So the centrifugal force at the equator, as a proportion of the force of gravity, is of the order of 0.03/10 =0.003, or 0.3%. At higher latitudes it will be less, presumably by a factor of the cosine of the latitude, falling to zero at the poles.

You can never get more energy out of a device than it consumes. Most attempts at doing so involve misunderstandings about...... things like gears on a car. In a gearbox, you can choose what combination of torque and rotational speed you want. If you double the speed you halve the torque. But power is torque x speed, so the power output stays unchanged. The same is true of any system that uses a lower speed element to drive a higher speed one. Nothing will multiply the energy for you, I'm afraid. In your proposed device, you seem to have an electrical power input from these magnets. The output you get will be no greater than the electrical power input, regardless of how you arrange fans of different sizes etc. Energy is conserved, i.e. it cannot be created or destroyed. This seems to be a fundamental principle of the universe. (Back at the beginning of the last century a very clever woman called Emmy Noether proved this must be, so if the laws of physics don't change with time. Or so I understand - I'm not a mathematician.)

I'm not sure I follow. Are you saying the Egyptians didn't know π but the builders of the pyramid (I presume you mean the designers) did? Are you then claiming the builders or designers were not Egyptian, but brought in from somewhere else?

Yes, exactly.

The surface area of a sphere is 4πr². If the radius of Kepler 22b is 2.4 x that of Earth, that would be ~9600 miles. So the surface area will be 4 x π x 9.6² x 10⁶ sq.miles ~1.2 x 10⁹ sq. miles if my arithmetic is right. Or in "ordinary" notation that is 1,200,000,000 sq. miles. So you can divide that between land area and ocean area as you wish. If you want ocean mass, however, as opposed to area, you have to calculate the volume of water, which means you need to say how deep you think the ocean is on average. You can then use the formula for the volume of a sphere 4/3 πr³. Since the water is a spherical shell around the planet it will be the volume at full radius, (call it R) minus the volume at the radius at the ocean floor (call it r) : i.e. 4/3 π(R³ - r³). You can then apply the density figure you want to use to get the mass. That would be for a planet whose surface is all ocean , so then you would pro-rate for the proportion that you want to be ocean.

That's interesting. However that would have been written about a thousand years after the pyramid was built, to judge by the most recent estimates of its age.

As it happens, only today I was reading a very simple explanation for why the base perimeter of the Great Pyramid divided by its height is very close to 2π. It seems the Egyptians may have used a trundle wheel, one cubit in diameter, to measure out the base at 280 revolutions from one corner to the diagonally opposite corner, and then built it 280 cubits high. So they automatically got a ratio involving π, without anyone at the time needing to know anything about it. I thought this was rather neat.

Yes the banned list is very entertaining, isn't it? Some of the entries seem to have been crafted with some care for humorous effect.

This seems to be incoherent rubbish. I'm off to bed.

That's interesting. Clearly even that part of it is more nuanced than what one reads in the papers - not surprisingly, I suppose.

This differential equation is irrelevant. In your ferrite ring, the vibration is excited by the AC current: either by the stretching of the coil I referred to or the magnetostriction effect or both. The vibration causes the contact force from the table to vary, since the surface of the ferrite in contact with the table is moving up and down. This accelerates the centre of gravity of the ferrite, first in one direction and then in the other. It is just like you jumping up and down on the spot.

No, the "active chlorine" % quoted on a bottle of bleach is a measure of the strength of the bleach. It tells you how much chlorine a certain concentration of hypochlorite is equivalent to. 2.5% means that the concentration of sodium hypochlorite (in your case) has the same strength, as a bleach, as a solution containing 2.5% dissolved chlorine. It behaves like a chlorine solution of 2.5% , even though sodium hypochlorite is not the same substance as chlorine gas. I understand you are concerned with possible corrosion of electronic components. My advice would be that your sodium hypochlorite solution is likely to be just as corrosive as 2.5% chlorine would be.

Right, so nothing about investigating the source of epidemics, which is what I asked you. That was my point: the WHO can only investigate with cooperation. Regarding your second point, there is no dispute that China was far too slow to report the outbreak - and you have quoted an international law they appear to have infringed. Now what? What do you propose to DO about that, given that the US has spent the last 4 years weakening and undermining just about every international institution, from the UN to NATO, to the WTO, the Paris Climate Agreement and, last but not least, the WHO? The Chinese will just laugh.

I explained the vibration of your washing machine twice, but you ignored it, just demanding all over again that we provide an explanation. Both I and @swansont have explained why your ferrite ring vibrates, and I have explained, twice, why that can lead to motion. But you have ignored it and now you are demanding all over again that we explain it. In neither case has there been any engagement from you with what we have had to say. If you will not even address our explanations, what is there for us to do? Repeat ourselves? As for Newton's laws, I will tell you, one last time, that Newton's laws require only that the centre of gravity of an object continues in a straight line at constant speed if no net force acts. If it is non-rigid, and part of it is in motion relative to the CG, then Newton's laws demand that there be a correspondong motion elsewhere, to maintain the CG moving in this way. As I told you before, gas molecules, floating in free space between collisions, vibrate. This is entirely in accordance with Newton's laws. You have got this wrong notion from somewhere that a non-rigid body, free from external forces, can't be in a state of vibration. That is just ballocks, I'm afraid.

There is no connection to your eccentric mass (washing machine - type) example whatsoever and I find it depressing that you have still failed to grasp how to analyse that example. It is commonplace for vibrating devices placed on nominally horizontal surfaces to move. The object is in effect jumping off the surface many times per second, so any tiny source of asymmetry of forces in the contact zone can cause it to move. This is why kitchen appliances like my blender have suction feet on them. Forget this crank nonsense about Newton's laws being broken.

There is certainly a kind of wilful asymmetry in thinking abroad at the moment that fails to recognise the emergence of China as a - basically unfriendly - world power with a chip on its shoulder and something to prove. The US political Right seems far more interested in hunting for scapegoats than in dealing with the epidemic - in fact positively obstructing efforts to do so, by turning simple countermeasures into political totems. Blaming China, or blaming Fauci, or blaming the WHO is not going to get anything useful done. It will just make everyone angry, which is how cooperation is destroyed. What standards are you referring to? What is there in the UN charter about investigations into the source of epidemics? I share your frustration, but we need to be geopolitical realists. So far as I can see there is no way to force China to accept an independent investigation from the WHO or anyone else, especially when there is no evidence they were responsible for the outbreak.

OK if it makes a loud sound it is vibrating. This will make it tend to move if there is any asymmetry in its contact with the surface it rests on, or if there is any force from strain in the the wires. It will also make it move more readily in response to gravity, if there is any slope at all in the surface it is resting on. Coils actually expand and contract in synch with the current flow. You have a conductor in a magnetic field, so it will experience a force at right angles to both, by Fleming's Left Hand Rule, which stretches and then relaxes the coil. So it will vibrate. (Electric motor armatures have to be very tightly wound for this reason - to stop the windings coming loose when energised as the windings stretch.) I think this vibration may be the source of the motion.

The WHO is not a police organisation. It relies on cooperation between sovereign nations. So it is hardly surprising that their power to force China to allow investigators in is limited. This reliance on cooperation has been true of world affairs since the time of the League of Nations. It's not great but it's a fact of geopolitical reality. So we may never know for sure what the source of the outbreak really was. But there is a very good chance it was of completely natural origin.

OK. So you have a high frequency alternating magnetic field in this ferrite ring, and when you energise it you find the ring slowly slides across the table. I notice the table has metal legs and that there are various large metal components also on the table. It is unclear whether or not the table is flat. I have two questions for you. First, if you hold the ring in your hand, do you feel any vibration, or when it is on the table, can you hear any sound from it? Second, what happens when you place the ring on a surface with no metal objects nearby?