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Physics, Astronomy & Cosmology / Re: How does gravity affect a caesium clock?

« on: Today at 12:15:16 »

We don't measure the frequency of the Cs transition! We use it to measure the frequency of an auxiliary generator because it is the SI definition of frequency. Admittedly there are wobbles, but whilst the kilogram is defined in terms of h, there are experimental uncertainties in every Kibble balance measurement: realisation of a base unit is not the same as definition.

Thanks to the electric wireless telegraph thingy, the cesium clock is entirely practical. I even have a tiny receiver in my car instead of a map. And the magical GPS system makes all the relativistic corrections for me!

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Physics, Astronomy & Cosmology / Re: Do you think sports is science?

« on: Today at 12:03:17 »

The aerodynamics of a spinning ball is (are?) crucial to many sports, and the greatest sport of all, gliding, is all about physics, meteorology and geography. Boxers and wrestlers spend a lot of time studying applied anatomy, and physiology is the key to track and field athletics. In fact it's diffcult to think of any physical competition where experimental sciences don't play a part, and if you want to include mathematics and statistics, you can add chess and backgammon to the list.

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Physics, Astronomy & Cosmology / Re: How does gravity affect a caesium clock?

« on: Today at 00:09:13 »

Nobody claims that a cesium clock is perfect, only that they are very very accurate

On the contrary, time is defined by the frequency of a cesium clock, which makes it perfect by definition.

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Just Chat! / Re: Can science prove God exists?

« on: Today at 00:05:23 »

First, determine what you mean by God. Then decide what you would consider proof of existence. Now look for that proof. Or, if you want to be scientific, look for disproof.

So far, I haven't come across anyone whose definition and chosen proof have stood up to scrutiny.   

You could postulate "somebody must be in charge of everything" which may not be disprovable, but he's clearly not on the side of homo sapiens, so I'm an antitheist.

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Physics, Astronomy & Cosmology / Re: How does gravity affect a caesium clock?

« on: Yesterday at 12:41:01 »

...or you could just extrapolate the gravitational red shift to infinity.

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Chemistry / Re: Making aluminum powder using angle grinder and aluminum profiles from windows?dding a bit oif ca

« on: Yesterday at 09:51:16 »

Problem with grinding aluminum is that it clogs the grinding disc and either prevents it working or falls off in large lumps! You  could use a coarse rasp or Surform blade, but good thermite requires a very fine powder, usually made by spraying molten aluminum into an inert atmosphere.

Since Al will rip the oxygen from Fe2O3, I very much doubt that adding a bit of carbon dust will stop it oxidising.

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Physics, Astronomy & Cosmology / Re: Is "Space" distinct from "nothingness"? (and the Vacuum)indeed an empty vac

« on: 24/06/2019 17:41:29 »

You can't use "is" and "virtual" in the same sentence! Stuff is either actual (you can touch it) or virtual (you can model it mathematically). A good synonym for virtual is "as if".

Space is indeed an empty vacuum until you introduce real particles between which the  Casimir and Van der Walls forces become apparent.

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General Science / Re: Why does my speaker sound different in front of a flame?

« on: 24/06/2019 17:28:12 »

1. The viscosity of gases increases with temperature, so the transmission loss through hot air will be greater

2. The flame area will be turbulent, leading to scatter of the sound waves

3. There will be an updraft, deflecting the sound waves upwards - it may sound louder if you stand on a ladder!

4. The speed of sound depends on temperature, so a cylindrical hot zone acts as a dispersing lens

5. The flames will contain all sorts of particles, which act as a sonic blanket.

Altogether a lot of physics in a very simple but very acute observation!

The propagation of sound through inhomogeneous and turbulent media is a crucial study in submarine warfare. Any prospective sci-fi authors out there might consider releasing plankton to attract a shoal of herring and thus hide a stationary sub. No charge for the idea, but please name the villain after me.

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Physics, Astronomy & Cosmology / Re: How does gravity affect a caesium clock?

« on: 24/06/2019 12:01:12 »

Relativity says either there is no "actual" frequency, or it is always whatever you measure at that point! Interesting that a mechanical wristwatch with an escapement wheel will keep perfect time anywhere in the universe but a pendulum clock will stop if g = 0.  Thus a pendulum clock does not measure time, but gravity!

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Technology / Re: Will this 2-probe oscilloscope produce an XY display?

« on: 24/06/2019 11:56:33 »

Can find no email contact for this firm only phone, but the blurb is there.

Recommend using the "chat" tab on their website - they are very helpful when it's active.

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Technology / Re: Will this 2-probe oscilloscope produce an XY display?

« on: 23/06/2019 22:39:29 »

Indeed, Pico, Hantek and other serious professional DSO plug-ins use a PC for control and display. The nice thing is that if you are serious about an art/entertainment installation, you can use the PC slave display output to drive a damn great projector.

Lissajous figures from raw stereo music are likely to be very messy but Pico software includes all sorts of filters, so you may be able to isolate the bass for a cleaner picture.

Funny how life has got more complicated and simpler at the same time. The old BBC "Tomorrow's World" introductory sequence (1965) had the music displayed on an analog scope and  captured on cine film - it probably took about 20 minutes to rig the whole take, from stuff just lying around in every recording studio!

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Technology / Re: How can renewable energy farms provide 24-hour power?

« on: 23/06/2019 22:23:32 »

Looking forward to reading your latest, SS. I think there is some psychic connection: I haven't thought much about energy storage since your last posting 18 months ago but it all came to mind this week during a trip to Bute and hearing about a hydrogen fuel-cell bus trial. Eminently practicable without flooding the Highlands. More anon!

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Physics, Astronomy & Cosmology / Re: How does gravity affect a caesium clock?

« on: 23/06/2019 15:26:06 »

So the frequency of resonance of the caesium atoms is identical in both settings, but when viewed from the perspective of the other, it appears to have changed?

That's relativity in a nutshell!  The electrons in the cesium atom have no knowledge of where they or you are, only that they are in the electric field of the nucleus, so the transition energy is independent of velocity. As it must be, since absolute velocity is meaningless.  The gravitational picture is more difficult to explain but a clock at point  A  in the universe can only transmit one tick at a time, so if observers at B and C  measure different frequencies  f_AB≠f_AC emitted from A, the difference must be due to their relative gravitational potentials.

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Technology / Re: Will this 2-probe oscilloscope produce an XY display?

« on: 23/06/2019 15:18:03 »

It will do the job if the scope has XY display facility. Picoscope and Hantek definitely do, and as I think I remarked earlier, Pico have been generous in the past with software help and mods, so should be no problem getting rid of the graticule and displaying on as large a screen as you like. 

Other DSO systems are available - these are the only two I have used personally, and I've had less success with Hantek software mods.

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General Science / Re: What will be the radiation exposure from 5G networks?

« on: 23/06/2019 15:04:46 »

tissue deterioration and premature ageing disruption of cell metabolism. Increased blood-brain barrier permeability. Melatonin reduction leading to insomnia and increasing cancer risks.

Just like life.

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Physics, Astronomy & Cosmology / Re: How does gravity affect a caesium clock?

« on: 23/06/2019 09:45:36 »

So what's actually changing about the way the caesium atom keeps time in each of the two conditions?

Nothing! The essence of relativity theory is that the airborne clock has no idea of its constant speed since all motion is relative, but each appears to the other to be losing synchronisation because their separation is changing. Not to be confused with gravitational effects, where acceleration or a difference in gravitational potential warps spacetime: again each clock continues to work in the same way, but appears to run at a different rate from the point of view of the other.

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Physics, Astronomy & Cosmology / Re: Is "Space" distinct from "nothingness"? (and the Vacuum)

« on: 22/06/2019 09:58:22 »

Creating a perfect  vacuum is as difficult as drawing a straight line, but who cares? Maths deals with straight lines, physics deals with weightless strings*, and in real life we just accept whatever is good enough.


*My father swore that he read an Indian exam paper with the phrase "you may ignore the weight of the elephant".

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Physics, Astronomy & Cosmology / Re: Is it possible to connect a second analogue display to an oscilloscope?

« on: 22/06/2019 08:48:37 »

e-Bay has dozens for sale, about half warranted as working.

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General Science / Re: What will the radiation be like when 5G gets implemented?

« on: 22/06/2019 08:34:16 »

BC: you are indeed mostly water, but hopefully held together by a layer of fairly dry epidermis with rather lower emissivity, and that value is wavelength-dependent. Conventional thermography tends to use near infrared and yields e ~ 0.9 but IIRC the value for longer wavelengths is lower, and as a gentleman of scientific standing I assume you also have a full beard and a hairy chest, which reduce e. However I will happily stand corrected if the spectrally weighted total is a lot more than my guess.

Your phone will have a "talk time" specification, or you could assess its total output from the battery mAh rating. 

Syphrum: Radiation is energy transmitted in the absence of a medium. In the radiation protection business it includes all subatomic particles as well as electromagnetic radiation, and with the gradual adoption of heavy ion radiotherapies, I guess it applies in principle to any projectile. Certainly at the mesoscopic end, the military talk about energy transfer by bullets and shrapnel!   

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Physics, Astronomy & Cosmology / Re: Is it possible to connect a second analogue display to an oscilloscope?

« on: 21/06/2019 22:46:05 »

It's not the most obvious feature as most people want to make measurements from a digital scope, but if you want to display a static waveform or Lissajous figure you can use a Picoscope plug in to a PC to capture the data, transfer it to Excel, then draw whatever graph you want from the spreadsheet, with or without a grid.

Other plugins (e.g. Hantek) are available but I think the Pico software is particularly transparent and adaptable.