mistermack

Electric and magnetic forces are action at a distance? 

Not really. They are action over a distance and time. The action takes time, even if it is fast. Not so different from throwing a stone.

You throw the stone. Time elapses and the stone travels. The window breaks. 

So I wouldn't call it action at a distance. It's action...-process over distance and time....-reaction. 

How that jumps to there being a god hasn't been explained. Why can't the laws of physics exist without a god? Just claiming that it is so isn't very good logic. Logic involves explaining how you get from one statement to the next, and why it has to be so.

Shame they can't read genes from fossils. 

My own feeling is that panspermia didn't happen, although there's no reason why it couldn't. I'm just guessing.

The earliest evidence of life is of very basic stuff, and I would have thought that panspermia might have introduced more advanced life as well, giving life on Earth a real kick start of more evolved organisms. 

But there might be good reasons why that couldn't happen I guess.

26 minutes ago, seriously disabled said:

Lets face it. Humans are just too stupid to figure everything out.

We can't even figure out on how life on Earth began or why some people feel pain way differently than others?

We don't even know what pain really is and how it is related to life and consciousness.

We don't even know what consciousness is and how it related to life and biology.

Stupid compared to what?

You have unrealistically high expectations of creatures whose brains evolved without any design, just by discarding the one's who couldn't survive long enough to breed successfully. I think, considering how and why we got here, we are punching way above our weight, and are freakishly intelligent, for an ape.

There is so much of this guff about, you have to develop a filter, or you will waste a significant chunk of your life debunking rubbish.

Surely there is enough in what you have written to convince anyone that it's rubbish? You need to turn off your curiosity at the very first clue, because it's too valuable to waste on these con-artists.

The time you waste on it could be spent on genuine science, which is equally amazing, and has the added bonus of being true and in line with the real world.

So the current thinking is that the dark energy is already here, hidden, in a mysterious form, and is gradually being converted to the increasing amounts of potential and kinetic energy ? 

Or could it be that there is a constant trickle of dark energy from an unknown source in so-far unknown dimensions?

I just wondered, as the Universe expands, is it gaining energy in some way?

If the Milky Way moves one kilometer further away from the Andromeda Galaxy, (ignoring it's existing motion), doesn't that mean that a stupendous amount of potential energy has been added to the system? Because of the distance apart being part of the energy equation?

Is there a known source for this, or have I got it wrong in the first place?

10 hours ago, Baron d'Holbach said:

 

Where's my prize now!  

 

No prizes, you're not the first to suggest it.  

Of course, the LACK of fossils outside of the known evolutionary sequences is good evidence FOR evolution.

If your rabbit scenario happened, the first question would be, 'do we know the full history of rabbit evolution?'

This new rabbit might be just adding to our knowledge, although it looks out of place at the moment. If we have a complete sequence of rabbit fossils, going from primitive to modern, over 50,000 years, and then you find this modern one dated at 75,000 years, you would want to look very closely, to see if there are any differences, because it might be a case of parallel evolution, producing a very similar rabbit to the modern one, going back more than 75,000 years, and then going extinct. Not very likely, but an expert should be able to tell.

Another possibility is that someone has doctored a later fossil with carbon isotopes, to make it give a false age reading.

Another possibility is that the dating system is at fault, rather than the theory of evolution. None of it is very likely though, so it would certainly cause a stir.

People often say "the theory of evolution" when they actually mean the theory of evolution by natural selection.

The theory of evolution by natural selection is the almost universally accepted explanation for the origin of all species.

But evolution was known about and widely accepted long before Darwin's work.

It just means that species gradually change from one form to another. Many people had argued in favour of that process, but nobody had offered a convincing argument for why it should happen.

Darwin and Alfred Russel Wallace independently worked out that it was natural selection that was the driving mechanism, with the popular simplification of "survival of the fittest" as the central idea behind it.

While nothing is ever a hundred percent certain, evolution by natural selection has so much evidence supporting it, and so little against it, that it's considered a fact for all practical purposes, and to believe otherwise, you have to be able to close your eyes to a vast quantity of virtually undeniable evidence.

Darwin was actually extremely bothered by doubts, because he couldn't understand why different characteristics could persist in a population, rather than fading out to a universal "blend" of characteristics, where all individuals became the same due to cross breeding. (like if you keep mixing paints with each other, eventually you end up with just one colour, a blend of all of your starting colours).

The answer, which Darwin never found out, was genes. A Bohemian monk, Gregor Mendel, was working on the laws of inheritance in the time of Darwin, but Darwin never heard of his work. It completely removes the problems that caused Darwin to have reservations, and the combination of natural selection and genetics being the explanation for the existence of life as we know it is as close to accepted fact as science gets.

So what most people refer to as the "theory of evolution" is actually a combination of evolution, natural selection, and genetics.

 

 

No, it's not.

Tis

In the case where the hanging points are lower than the pivot, you get the following

Yes, I could see that from your previous post.

If you mentally picture an extreme case, of the arms sloping at 45 deg, it's obvious that the arm that dips is moving closer towards the centre line, and the arm that rises is moving away, so one loses torque and the other gains, giving the resultant return force.

 

 

Because of the CoM being offset in the horizontal direction, not the vertical. Adding masses to the pans doesn't shift the CoM in the horizontal direction, only the vertical, and does not supply a restoring torque unless one is already present. Which is not there if the CoM is centered in the horizontal direction.

Agreed. That's basically what I said.

 

Neutral scales would be useless - they would just keep tipping towards the heavier side until they were vertical. With no weight, they would remain in whatever position they had been left in.

It's hardly likely that scales would be designed without a platform just below the pans. So that's not really a practical problem.

In the practical world, I would think a small amount of self-levelling would be tolerable without losing too much sensitivity.

Yes, that's a variable I hadn't considered.

In practice though, would you design a self-levelling setup anyway? Surely you lose some sensitivity or accuracy, if the scales are self-levelling.

And they would be frustrating to use if they were inherently unstable.

I would want scales that are neutral, so that the slightest inequality results in clear unrestricted movement towards the heavier side.

Maybe a small amount of self-levelling would be tolerable, if there was a visual aid like a pointer to clearly show when the scales are balanced.

 

 

 

OK. No change, even though the CoM is below, just from movement. But now put equal masses on the pans. The CoM has shifted lower. Where is the restoring force/torque?

Can you really refer to the centre of mass of an apparatus with freely moving links? It has an instantaneous centre of mass, but doesn't necessarily have the same CoM as things move.

In this case, with added equal weights on either side, the two pans and weights will cancel each other out in the same way as empty pans.

The restoring force will be purely provided by the moving CoM of the rigid beam, as before. The swinging pans, with any weights you care to choose, will always cancel each other out.

 

 

We were talking about contributions to center-of-mass with regard to the vertical.

I think the same applies as the horizontal. Assuming that the sides are symmetrical, the movement of the left side up will be exactly matched by the right side down, resulting in no change in the position of the CoM.

The exact same amount of mass rises the same distance, as what falls on the other side.

So in the case of loose pans, they will have no overall effect in returning the balance to the horizontal.

It will just be the centre of mass of the beam, rotating sideways and upwards, that provides the return force.

If the pans are loose, their own collective centre of mass will remain central, unlike that of the beam.

It's not obvious to me that the CoM of a straight beam balance with pans below it is displaced from center, even though it's below the pivot, if the pivot is in the CoM of the bar.

The CoM has to be displaced on a simple beam arrangement, if it's above or below the pivot.

If the pans are fixed then the beam and pans are a single object who's shape doesn't alter. The CoM will remain in the same place and will have to rotate with the beam.

If the pans are loose, then they just cancel each other out, so the centre of mass location will be unaffected, and the CoM of the beam will still rotate around the pivot, unless it's exactly AT the pivot point.

 

 

But it's not because the CoM rises; that explanation does not suffice. It's because it deviates to the side, so there is a torque on it. If you could engineer a device whose CoM remained centered but was below the pivot, it would not return to horizontal.

I agree about the torque. But equally, if you could engineer a device whose CoM didn't rise, then it wouldn't return to the horizontal either. The torque, and rising CoM are inevitably going to be there in any simple beam, with CoM below the pivot.

The energy to return the beam to horizontal position gets put in when the CoM is raised.

Apart from the initial costs? How come they don't count?

The cost of running stainless steel pipes over all of the forests would be ludicrously expensive.

And salt water would not be good for the land. And yes, the running costs would be incredible, for such a tiny return.

The CoM has to be displaced to the side from the center line, which is accomplished by having the arms be angled or curved, as described by Tim88. You can have a balance whose CoM is below the pivot in equilibrium. Even the straight arm balance can have a CoM below the pivot, because the pans have mass.

That's what I was saying. You can design the beam so that the centre of mass is below the pivot, and this will naturally return to the horizontal.

COM at the pivot, and the beam will be neutral, remaining where you put it.

COM above the pivot, and the beam is unstable.

Obviously, any manufacturer will design a balance with its COM below the pivot for convenience, so that it self-levels.

When the balance is tilted, the COM will rotate, rising from it's lowest position, so gravity will pull it back down when released.

I haven't read all of the posts in depth, but it seems to me that it simply to do with the location of the centre of gravity of the balance beam when unloaded.

If it's below the pivot, then the beam will naturally return to the horizontal, because any tilt on the beam causes the centre of gravity to rise.

So the beam is levelled by gravity acting through the c of g.

If the c of g was above the pivot, the beam would be unstable, and want to flip to whatever side it's tilted to on release.

 

Otoconia breaking off could be responsible, and would account for extreme vertigo.

Thanks. I don't think that would cause my symptoms though, because it comes and goes.

I had a bad fall as a child, hitting my head, and am deaf in one ear, and get tinnitus since the fall, so I'm guessing that that has damaged something.

But it was ok for over fifty years, apart from a bit of deafness and tinnitus.

About 10 years ago I was having a coffee at the golf club one Friday (might have been a Tuesday) morning. I was on my own waiting to go and practice or play. I stood up and looked outside at the 18th green and BAM - all of a sudden it felt as though I Had accelerated fast by about 2 foot to the side... The feeling was in my brain/head - I felt nothing in the rest of my body, just this sudden sideways 'shove to the side. It was a little nauseating at first but it passes quickly.

 

Many things went through my thoughts... was the earth displaced? (no) was it a quake? (no), did anyone else notice this? (looks around - no).... was it imagination?... (hmmm doubt it, felt VERY real). Was it a tiny tiny stroke or blood lot moving? (Maybe, how would I know). I still do not know what that was... maybe I should have reported it to a doctor, but it never happened again and I had a busy day of golf practice planned so I just carried on.

 

Whatever it was - I am pretty sure the occurrence was biological rather than physical. Maybe the same goes for the perception of the room moving for the OP? Hard to tell.

I had something similar happen to me a few years ago. It came out of nowhere, and all of a sudden I didn't know what was upright, or moving or still. It was so severe I called an ambulance thinking it was a stroke. But unlike you it persisted, and I was thoroughly checked out with full MRI scan of the head etc. Nothing faulty was found. But I still get some dizziness and headaches on a smaller scale.

My theory is that it was related to the inner ear, which is incredibly delicate. Could be mechanical, or nerve related.

But it was a hell of a shock.

All sorts of stuff is possible. We only perceive things properly, when everything is working properly.

Even a change in medication can cause amazing symptoms, on occasion.

You only have to read the small print to get an idea of what some people experience, from some fairly run-of-the-mill medicine.

To get a mental picture of it, I would picture a ball bearing on a hard surface.

If the surface is slightly downhill, the ball accelerates horizontally. So it loses potential energy due to it's vertical drop, and gains kinetic energy in a direction that it's rolling, at nearly 90 degrees to the drop.

The vehicle is basically rolling downhill as it drops in it's orbit. Instead of it's weight being balanced by a hard surface, it's balanced by the effective centrifugal force of it's orbit. But the effect is the same. It speeds up in a direction at approx 90 degrees to it's drop.

There is no doubt that the atmospheric drag is the major cause of the loss of altitude.

My point is that the atmospheric drag is a force acting opposite to the motion of the satellite; it seems a paradox to me that the drag accelerates the satellite.

There is no doubt that that's true, but how that can be explained?

I think you are thinking of the satellite as travelling in a straight line. It's not, it's actually continually FALLING towards the Earth, in a constantly changing direction.

So the speed that it gains, through a drop in altitude, (like a falling stone), is redirected to a rise in it's rotational velocity.

Something similar happens when a spinning skater pulls his arms in towards his body.

You are true but change in kinetic is happens due to change in momentum & rate of change of momentum is force. So, how could we avoid any force action in this event.

Basically, you are talking about the same thing. The only difference is the method you use to describe it.

There is a thing called gravity that causes mutual attraction between masses. You can model it as a force, or as curvature of space time. But you are talking about the same thing.

General relativity works as a model of gravity, to a high degree of accuracy.

If you look on the wikipedia page for general relativity, you will find this telling passage :

" Some predictions of general relativity differ significantly from those of classical physics, especially concerning the passage of time, the geometry of space, the motion of bodies in free fall, and the propagation of light. Examples of such differences include gravitational time dilation, gravitational lensing, the gravitational redshift of light, and the gravitational time delay. The predictions of general relativity have been confirmed in all observations and experiments to date."

So if you want to stick with classical physics, and ignore GR, you run into problems.

That might be true, but it's best not to lose sight of how and why our minds evolved, and those of whales.

Mind and body evolved to reproduce our own genes. Anything else is a byproduct.

Our own instincts to protect other species are their because they spill over from our instinct to protect related members of our own species.

It happens more in long-lived social animals which don't produce large numbers of offspring. But not exclusively.

There's an instinct to protect the young in a lot of mammals, even surprising ones.

I've seen video of lionesses protecting a fawn after killing it's mother, also leopards protecting baby monkeys.

It's usually females, and it may happen when their female hormone levels are high.

It's not always the mind in isolation that drives behaviour, sometimes the hormones can drive the mind.