1

General Science / Re: What's the resolution of the human eye?

« on: Yesterday at 16:23:48 »

Angular resolution: about 1 arcminute, approximately 0.02° or 0.0003 radians, which corresponds to 0.3 m at a 1 km distance.

So roughly 3300 linear pixels in the centre field, which is fairly unimpressive compared with most birds or even a cheap desktop scanner. The clever bit is the integrating and interpolating capability of the brain. I remember noting that I could clearly see the 0.5 cm diameter tow rope trailing from an aeroplane 300 m above me - well below the theoretical resolution of a human eye but clearly discernible by a combination of integration, interpolation and training. Much more difficult to see the rigging of a small boat or radio mast at the same distance because they aren't moving across the visual field.

2

Physics, Astronomy & Cosmology / Re: Is it possible for something to absorb light without reflecting it?

« on: Yesterday at 12:12:46 »

A "black body" comes close to a perfect absorber. If you drill a small hole in a large hollow sphere, almost everything that enters the sphere stays inside it.

3

Physics, Astronomy & Cosmology / Re: Can we measure the one way speed of light?

« on: 20/06/2018 17:41:33 »

the fabric of space

Please set down the physical characteristics of this wondrous fabric. Density? Elastic modulus? Viscosity? ε_FS and μ_FS?

If I can move relative to it, what is it fixed to?

4

Physics, Astronomy & Cosmology / Re: Can we measure the one way speed of light?

« on: 20/06/2018 07:30:06 »

Wholly different experiment, wholly different result.

In my experiment the source does not move during the measurement.The only moving part is the locally oscillating part of the receiver, and the measurement is of the Doppler shift between the fixed and moving parts of the receiver when the direction of the incoming beam is fixed.

Your "ring experiments" are also irrelevant. c is the speed of light in vacuo, not in a medium. c_m is subject to all sorts of variations.

5

The Environment / Re: Is the greenhouse effect a stupid mistake?

« on: 13/06/2018 07:40:16 »

In summary, you seem to be saying that clouds dominate the radiative heat transfer to and from the surface of the earth. That is obvious to anyone who has ever stood underneath one, but it seems to have escaped the notice of so-called climate scientists who persist in counting fleas like CO2 and CH4 whilst studiously ignoring the H2O elephant they are riding on. Thus leading to statements like "global warming has altered the rainfall pattern" when it is obvious that the rainfall pattern is what determines global temperature.

6

Technology / Re: could this clockwork supply a city with renewable energy?

« on: 12/06/2018 23:49:26 »

This is a great invention ,  great as a dynamo or electrical motor, I wonder why da vinci didn't invent it?

Practically every clock built before 1400, and quite a few modern grandfather and cuckoo clocks, use a falling weight as the energy store. da Vinci didn't invent it because it was already old technology before he was born.

Short-term high power interventions like Dinorwig are used to bridge a few minutes' gap until conventional coal or gas powered stations can be brought on line in periods of sudden demand. They have no value in terms of stabilising the grid against the enormous and long-duration fluctuations caused by windmills, tidal mills or solar cells. Once the grid becomes more than 20% dependent on unreliables, each new generator needs to be backed by at least 5 days' storage capacity, just as with coal, gas or diesel stations, which is why "free" electricity is actually uneconomic - the energy density of non-chemical stores is pathetic..

7

Technology / Re: could this clockwork supply a city with renewable energy?

« on: 12/06/2018 10:13:39 »

22.5 million tonnes of rock is a plug 1 km high with a cross-sectional area of 1000 m², that is, about 7 times the mass of the Hoover Dam (I would use concrete rather than loose rocks, for obvious reasons).

You might be able to cast this mass at the bottom of a 2 km deep hole x 35 m diameter, then haul it up 1000m  on the ropes BC has designed. So you need a primary shaft that will span at least 35 m and two primary bearings capable of carrying a load 1000 times greater than any bearing yet produced. These will need foundations....it's beginning to look like an order of magnitude bigger project than anyone has ever attempted.


Why do I mention the Hoover Dam? Because it works, powers Las Vegas, and is by no means unique.

8

Physics, Astronomy & Cosmology / Re: Can we measure the one way speed of light?

« on: 10/06/2018 11:37:30 »

No.

ε₀ and μ₀ are measured in entirely separate, static experiments.

If the value of c depended on direction, at least one of these would have to be a vector so you would always get different values for either ε₀ or μ₀ depending on the polarity of the applied electric or magnetic field. You don't.

For anyone with a real interest in experimental physics it is worth noting that the relative values of ε_xyzand μ_xyz for some materials are indeed anisotropic tensors and the magnitude of c does indeed vary with the orientation of the material. The fact that the resulting birefringence effects are independent of the orientation of the material with respect to the fixed stars, phase of the moon, or anything else, strongly suggests that there is no aether or other universal frame of reference, so c₀ is independent of direction.

9

Physiology & Medicine / Re: Is it possible to be addicted to online posting?

« on: 03/06/2018 10:03:28 »

Heinz Wolff had an interesting take on mobile phones. He pointed out that our species depends on collaboration and communication to a greater extent than any other mammal - very few of us could survive without other humans, and even Robinson Crusoe depended initially on tools made by someone else. As a result, we are inherently a chattering species, like chimpanzees but more so.

Mobile phones and their derivatives allow us to choose from a wider group of chatterers and collaborators, with little chance of harm or exclusion from the whole group if we dislike one or two members. So whilst we are "herd-wired", picking and choosing our virtual herd is even more satisfying than family and neighbours.

Teenagers being wired to rebel, and scientists being self-selected as skeptics, we can immediately identify two groups who may find on-line communities more enjoyable and accepting than real ones.  The dangers are obvious.

10

Just Chat! / Re: Here is Practical Explanation about Next Life, Purpose of Human Life,

« on: 27/05/2018 23:19:16 »

and nobody in his right mind considers death to be a bad thing.

You are saying death is a good thing?   

Without it, the world would be packed full of animals fighting for food, air and pensions. You would have been born into a world dominated by dinosaurs or possibly their predecessors who lived in an atmosphere that could not support humans. No cell in your body could die, so you would actually be a malignant tumor, not a human being, as would every other living thing. There being no effective means of killing anything, whatever minor infection you might have would develop into an infinite torture. Or you might live forever whilst being digested by a carnivore. Death is what makes life tolerable, and the finite nature of life is what makes every day exciting.

11

Physics, Astronomy & Cosmology / Re: Can we measure the one way speed of light?

« on: 27/05/2018 23:01:12 »

If V_AB ≠ V_BA then the value measured by any experiment will depend on the direction of AB.

This is not found by experiment.

Therefore the "one-way" speed of light  is the same as the "two-way" speed.

12

General Science / Re: What keeps planes in the air at high altitude?

« on: 16/05/2018 23:59:31 »

The lift force generated by a wing is given by the formula L = ½ρv²SC_L where
ρ = air density
v = speed through the air (true air speed)
S = wing area
C_L = lift coefficient

S and C_L are generally fixed by the design of the wing, so as ρ decreases with height, we have to fly faster to maintain L at high altitude.

At 35,000 ft, ρ is about one third of the value at sea level, so v has to be at least √3 times the minimum required to sustain flight at low level (stalling speed).

Interestingly, the air speed indicator on an airplane actually measures ram pressure P in a forward-pointing tube (the pitot tube) and P = ½ρv², so the indicated air speed (IAS) for a given L doesn't vary with height.

Fortunately, drag force D has the same relationship D = ½ρv² A C_D where A is the effective cross-sectional area of the aircraft and C_D is the drag coefficient. 

Thus both lift and drag are related to IAS, but the true air speed TAS = v which increases as ρ decreases. So the higher we fly, the faster we cover the ground for a given fuel consumption. 250 knots IAS ≈ 425 knots TAS at 35,000 ft - definitely worth the effort of getting to altitude!

13

Physics, Astronomy & Cosmology / Re: Are clocks ticking faster where gravity is stronger?

« on: 08/05/2018 22:45:09 »

The only way to measure g at a point, is to take a gravimeter there.

The way to measure gravitational potential at a point is to take a clock there.

14

New Theories / Re: Are Pyramids an ancient way of wheel balancing?

« on: 06/05/2018 23:54:19 »

"My planet needs balancing. It wobbles at 1000 mph."

"Well, squire, I can put it on the balancing machine and fix a few pyramids to it, but that will only solve the problem at one speed. Trouble is, you've got the old model planet, with lots of water on the surface. Very good for supporting life, but it sloshes about, especially if you have the moon option - pretty enough at night, but a real bugger to keep steady in a complex orbit."

"OK, let's do the pyramids on this one, and I'll look around the showroom."

"Good idea, sir. Mars might suit you: two moons but no surface water - predictable on corners and if I may say so, a bit of a man's planet. 'Course if you're looking for a babe magnet, we've got a nice Venus: no moons, very pretty gas clouds, keeps one face to the sun, stable and easy to drive. Mercury is a bit of a boys' toy - hot, fast, not very comfortable. Meanwhile I'll stick some pyramids around the equator, and if that doesn't to the trick, we'll add a Great Wall."

15

General Science / Re: How to calculate fan power - formula?

« on: 05/05/2018 11:00:03 »

The equation P = ½ρAv³ is correct. ρ is the density of air, A the area of the fanduct, and v the exhaust speed.

However this only calculates the power transferred to the air. To calculate the fan speed you need to know its efficiency, which is a  complicated and nonlinear function of the blade geometry and v. That said, if you assume 100% transfer at the optimum speed for a given fan, then the swept volume per second is Av and each blade sweeps  an area A ω times per second where ω is the rotation speed, so you can calculate ω for a fan with n blades.

16

Physics, Astronomy & Cosmology / Re: How fundamental is time?

« on: 04/05/2018 17:20:20 »

I think Einstein pointed out that time is what prevents everything from happening at once.

So no problem with the Big Bang: it was the event when everything did indeed happen at once.

17

General Science / Re: Can you solidify exhaust gas emissions from a ship?

« on: 19/04/2018 10:56:40 »

It's an interesting idea.

Carbon dioxide is not a pollutant. It is an essential component of the atmosphere, without which there would be no plant growth and life would cease to exist. If we grew more trees (or at least stopped deforestation) Mother Nature would take care of the CO2.

The other stuff can generally be precipitated electrostatically (unburned hydrocarbons and solid particulates) or dissolved in water (sulphur oxides, nitrogen dioxide) to some extent.

But whilst rocket science is very simple, rocket engineering is a lot more difficult. Whatever system you add to your ship/rocket/car/aeroplane  will add cost and weight, increase maintenance costs, and reduce performance. You might devise a scrubber that removes 90% of particulates etc at "high-seas cruise" power, but that stuff would eventually settle in the sea anyway and be eaten by some bug or other. The real problem occurs close to land when you are using full power to accelerate or manouver, belching more black smoke than your scrubber can remove. If you increase the scrubber capacity, you will be carrying extra deadweight and capital during the cruise phase.....

18

New Theories / Re: Ok, lets rumble, I challenge the world.

« on: 15/04/2018 00:41:23 »

Pseudoscience, logorrhea and a childish rant discredit their author without the need fo third-party intervention. Sound and fury  can be entertaining on a stage, but this garbage is just boring.

19

Physics, Astronomy & Cosmology / Re: How far has the photon travelled?

« on: 08/04/2018 19:41:36 »

Nothing wrong with the question at all. We measure distance by bouncing photons off things (radar, lidar, interferometry) or exchanging encoded photons (DME) on the presumption that c is constant.

20

Just Chat! / Re: pmb is mentally ill

« on: 07/04/2018 08:19:03 »

She called the police and told them I'm suicidal and they put me in a psyche ward for a week.

Since when has suicide, or more to the point, thinking about suicide, been a crime? When was the Boston Thought Police Department founded?

Time you moved to Florida, where objecting to being killed evokes Presidential scorn.