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General Science / Re: history assignment help

« on: 20/12/2021 08:21:18 »

Sorry mate, but all spammers are history on this forum

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Chemistry / Re: Why does my hydrochloric acid produce negative pressure in its container?

« on: 28/05/2021 02:38:10 »

How much does the temperature change in your garage (or wherever you are storing the acid)?

If you close the barrel when it's warm and then it cools down, the pressure inside will drop significantly, causing it to crush in. Or, if the seal is not great, then when the barrel warms up some vapors can escape, and then as it cools the lid is pulled back down firmly into place as the pressure inside drops (kinda a one-way valve).

Hydrochloric acid will do this more than water (and less than gasoline) because of the relationship between vapor pressure of the liquids and temperature: if the temperature varies between 20 °C and 30 °C, water's vapor pressure only changes by about 10^–10 atmospheres (0.000000001% reduction in pressure inside). In contrast, concentrated HCl (35%) will change by 0.08 atmospheres (8.0% reduction in pressure inside).


Screen Shot 2021-05-27 at 9.31.57 PM.png (466.09 kB . 2204x1148 - viewed 12546 times)
http://wxjs.chinayyhg.com/upload/Files/Journal_of_Chemical_Engineering_Data/1956-1-/10-12.pdf

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General Science / Re: Buy Spam Online for Sale USA

« on: 07/04/2021 23:47:06 »

Hi all

boppity boppity time.

Is that a medical term?

Great stuff this spam. So, do you eat it or just smear it all over??

I believe the culinary experts would recommend it as an aid for battering 
just before you deep fat fry it

Spam fritters for everybody.
wonder if they do a mars bar version ?

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General Science / Re: SPAM TUB SPECIAL - The Washing Machine SPAM Service Center

« on: 17/03/2021 23:42:27 »

So my washing machine caught fire today
The good news is I was able to get my washing and drying done all in one go.

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General Science / Re: Is White Chocolate real Chocolate?

« on: 18/01/2021 11:20:21 »

I adore the proper, 90% cocoa, dark unadulterated stuff

It has the advantage that you can leave it on your desk and nobody nicks it (well, not twice, anyway).

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Plant Sciences, Zoology & Evolution / Re: Can we use Japanese Knotweed to green the deserts?

« on: 20/12/2020 22:14:07 »

Couldn't we find a use for the knotweed - such as feeding livestock on our farms, or making paper and cardboard  from it?

If it was good for something, it would be a crop rather than a weed.

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Geology, Palaeontology & Archaeology / Re: What is this round-shaped pebble with a conical end?

« on: 08/11/2020 11:41:26 »

I would guess at Echinocorys Sp. but it's a long time since I dabbled in that sort of thing.

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Geology, Palaeontology & Archaeology / Re: What produces this strange chipped pattern on the surface of this stone?

« on: 12/10/2020 22:03:04 »

The polygon patterns make me think this is organic in origin, possibly fossilized coral?

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Geology, Palaeontology & Archaeology / Re: What produces this strange chipped pattern on the surface of this stone?

« on: 12/10/2020 15:06:13 »

...... it doesn't explain the mechanism of its appearance, which I am eager to know...

This is a guess, but it looks as though the soft clay has been lying on a bed of pebbles.

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Question of the Week / Re: QotW - 20.10.05 - Which is better for you, hard or soft water?

« on: 05/10/2020 22:25:13 »

If you fall from 100m up, it doesn't make much difference....

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Chemistry / Re: Can Sulphites be removed from wine other than by adding hydrogen peroxide?

« on: 02/10/2020 15:14:37 »

The whole point of adding metabisulfites to wine is to preserve the flavor and inhibit secondary fermentation. Boiling the wine will leave you with a residue of sticky grape sugars and a tiny trace of potassium sulfite, and some rather raw brandy with a hint of sulfur dioxide in the distillate.

Given the choice, I'd rather drink my Mouton Rothschild as it came in the bottle, along with whatever additives the good burghers of Pauillac have deemed fit to use for the last 170 years.

My own garden produces an adequate grape juice, and I sometimes add a hint of  Na₂S₂O₅  to stop it turning into Chateau Calverd, or after adequate fermentation to prevent the Grand Cru turning into expensive vinegar - Sarson's Malt is a better match with chips.

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Physics, Astronomy & Cosmology / Re: Why does angle of reflection equal angle of incidence?

« on: 15/09/2020 12:30:09 »

Can you give me the gentler version first to get me started please?

Particles like balls also obey angle of incidence = angle of reflection (if you ignore gravity, and the fact that balls tend to start spinning when they run into things). At least snooker gets around the gravity problem....
- The motion of the ball can be broken into two components of momentum:
- One parallel to the cushion, which is not affected by the collision
- One perpendicular to the cushion, which is reversed for an elastic (energy-conserving) collision
- This produces a scenario where angle of incidence = angle of reflection
- You could extend this to a photon striking a mirror...
- Or the molecules carrying sound, where the large-scale orderly motion of the sound wave (longitudinal wave) is superimposed on the general random movement of air molecules

Water waves (transverse waves) also obey the angle of incidence = angle of reflection if they run into a vertical wall.
- The wave front will move ahead at a certain velocity when in a uniform medium.
- When a water wave strikes a wall, the horizontal amplitude becomes zero perpendicular the wall, but the vertical amplitude increases (conserving energy)
- The energy stored in the increased amplitude is released by the water moving away from the wall, producing an outgoing reflected wave.
- The part of the wave moving parallel to the wall does not contribute to the reflected wave, so you end up with the traditional law of reflection.

After that, I'm out of analogies. Apply Maxwell's equations in a simulation package....

the bit about waves cancelling each other out has got me confused.

A moving wave front can be modeled as a new wave radiating from every point on the wave front. This myriad of point sources cancels out everywhere except for the solution where the wave moves ahead. This effect can be seen in the classic double-slit experiment, where both slits effectively become a point source of radiating waves.

When a wave hits a reflecting surface, you need to take into account the boundary conditions.
- For an electromagnetic wave, this includes the current induced in the metal by the electromagnetic wave
- Adding up the contributions from every point, the signal cancels everywhere except for an outgoing wave which obeys the law of reflection.
- If you modify the mirror so it is periodic (like a diffraction grating), there are multiple angles where the sources combine constructively, producing multiple outgoing waves. This does not obey the "traditional" law of reflection. (the exception proves the rule...)

See: https://en.wikipedia.org/wiki/Double-slit_experiment
https://en.wikipedia.org/wiki/Diffraction_grating

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Physics, Astronomy & Cosmology / Re: If everyone in the world went swimming at the same time, would sea level rise?

« on: 05/09/2020 04:28:45 »

Very good point about the amount of available coastline!

But wouldn't the rate at which people were getting into the water be slower than the rate of water redistribution?

Also, presumably bringing all that mass close to the seashore would depress the land there a bit, so sea level would apparently rise (by a picometre or so?), and all the gravity associated with those people would pull up the water more, making a further apparent rise, surely?

OK, let's iron out a few variables.  Suppose the weather is nonexistent and the water is mirror calm all over the Earth.  All the people are already at the shore but waiting, so their gravity isn't going to change much by a small amount of motion. We remove the moon so tides go away. Can't measure a micron of sea level if it's boinging up and down with the tides.

That said, we have two scenarios: Do it quick or do it slow and wait for a new equilibrium to form.

Quick method:  A relatively small group of people jump into a tight bay and the water level rises there in accordance with the new volume displaced. That might be even a centimeter.  The water eventually runs out of the bay, but this is the quick and dirty method here. We're not measuring the sea level with a stick in the middle of the ocean (which is unaffected for hours by this), but just a local measurement. What people are doing elsewhere in the world is immaterial for the quick method. You get a temporary local sea level rise due to the local group going in.  The change causes a tsunami of sorts that takes time to get to places not near shorelines.  Point is, with the quick method, it's the local group that matters, not the whole population of Earth getting in the water.  It seems not in the spirit of the OP, so we instead go to:

Slow and permanent method:  The entire population gets in the water and stays there until a new equilibrium forms, which might take days (or much more!).  The sea level rises in accordance with a calculation similar to what BC did in the initial reply.

The surprising part of the answer for this is that it doesn't matter what water you get into.  I have a small waterfall in my back yard with a pond that could hold probably a dozen people submerged.  Suppose 12 people do that instead of wading into the ocean.  Sea level rises just as much (after some time) due to that. They don't have to be in the ocean at all. The people displace their weight in water which exits the pond that much sooner and adds their mass to the ocean after a day (in my case).  My brother can do the same thing where he lives and it would take decades for the sea level to rise from his action, but it would eventually. He lives near water that runs into Lake Superior, a lake that drains so slowly that any change to its level might linger for literally decades.  But sea level would rise eventually due to my brother sitting in a nearby pond.

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Physics, Astronomy & Cosmology / Re: If everyone in the world went swimming at the same time, would sea level rise?

« on: 04/09/2020 12:55:25 »

A good thorough answer from B-C, despite the one error Evan points out.

I'd like to mention what it would take for all of humanity to get into the ocean "at the same time". What is the length of the combined shoreline available to humans?  Some of the places it would take some time to get from the beach to a swimming depth.
A rough estimate of the shoreline is something like half a million km which yields a wall of people around 10 deep. So that's not unreasonable.  It takes less time for 10 people to enter the water than it does for any one of them to get to a swimming depth, at least in some places.  In other places, people 10-deep are jumping off cliffs like lemmings. Jumping off a boat doesn't count since anyone in a boat is already contributing to the sea level.

Also, the sea level will rise at the shores far more than those 2.5 micrometers since all the new volume is there and it would take time for that displaced water to reach the places in the ocean where people are not doing this.

Water evaporates from the ocean at a rate of about 16 billion kg per second if my sources are correct. All of humanity masses maybe 30 times that, so if they all manage to get their 10-deep line into deep water in under half a minute, they might actually out-pace the rate at which the ocean empties itself.

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Physics, Astronomy & Cosmology / Re: If everyone in the world went swimming at the same time, would sea level rise?

« on: 04/09/2020 10:55:17 »

According to this
https://www.scientificamerican.com/article/antarcticas-ice-shelves-have-lost-millions-of-metric-tons-of-ice/
"Antarctic ice shelves have lost nearly 4 trillion metric tons of ice since the mid-1990s,"
And that caused a sea level rise of the order of 20 cm.

People weigh about 50 Kg (most people are children) so there are about 20 people to the tonne.
And there are about 10 billion people so that's about 500 million tons of people.
People have roughly the same density as water- we more or less float- so we would add as much depth to the sea as half a billion tons of water.
That's about 8000 times less water than came from the antarctic (I'm ignoring the other ice sheets to make life simpler).
So the rise in sea level from a mass swim would be something like 2.5 micrometers.

If you got bored, you could find the area of the world's oceans- it's about 1/3 of the area of the Earth, and divide the volume of the people (about 500 million cubic metres) by that area and get a better estimate of the depth increase.
You could sharpen up the estimate of the volume of people too.

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Physics, Astronomy & Cosmology / Re: Is it likely our planet had rings?

« on: 24/07/2020 05:53:17 »

I do seem to recall Earth being depicted as having a temporary ring system after the Theia collision on one television documentary. That ring was shown to coalesce into the Moon.

You might be interested to know that the minor planet 10199 Chariklo has a ring system, despite being a mere 232 kilometers across: https://en.wikipedia.org/wiki/10199_Chariklo#Rings

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COVID-19 / Re: What's the current opinion on masks to reduce Covid-19 spread?

« on: 07/06/2020 12:59:26 »

Aha! The Cummings-Johnson design: glittery, with a hole in the middle.   

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COVID-19 / Re: Why can't we re-use PPE?

« on: 30/04/2020 19:35:16 »

By the time you have resterilised a latex glove, both inside and outside, it's pretty useless as a glove, even if it isn't torn or punctured. Likewise single-use aprons: very difficult to sterilise with ethylene oxide, not washable, and distorted to uselessness by steam. You might collect them, remove the blood and gunk (by hand!)  and sterilise in bulk with a cobalt irradiator, but the machines are expensive and pretty well full of urgent items like syringes, and if you knowingly begin with infected material, you can't rely on batch sampling to assure product sterility - you have to test every one!

The point of a HEPA filter respirator is to trap infectious droplets. So if you have a washable (plastic) matrix, you end up with a large volume of infected water and a wet filter with a few viruses. So you dry the filter with moving air and disperse virus (a) into the public water system and (b) into the factory air. Bag, bin and burn, please.

Cloth gowns can be laundered but they are surprisingly fragile and have a hard life in the ward or theatre, so they need to be inspected before repacking to make sure there are no gaping holes or missing tapes - all very labor-intensive in an expensive sterile area, so may not be first choice, and in the case of high infectivity, at some point you will have a bin full of evil to store in the ward then move along a public corridor and unpack in the laundry. Bag, bin and burn paper if you want to save lives.

Hospitals do clean and re-use crutches but most are stolen or at least forgotten because the discharged patients don't know how to return them! Crutch hunting and wheelchair tracking is a major activity of the Red Cross! 

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COVID-19 / Re: Why not use UV C blood irradiation to neutralize SARS CoV 2?

« on: 21/04/2020 11:53:51 »

Maybe they should try sound waves of a frequency which would destroy the virus.

OK, obviously that would need to be quite a high power density.
What frequencies did you have in mind?
Remember- it has to be a frequency that's not absorbed by human tissue or you will kill the patient, rather than the virus.

I was thinking of taking the blood out through a tube and back in and using the sound on the blood passing through the tube.

Some research here https://www.livescience.com/7472-kill-viruses-shake-death.html

OK, any idea what the range of 60 GHz sound waves is in blood?

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COVID-19 / Re: Could the infection rate be significantly underestimated?

« on: 17/04/2020 16:51:02 »

A reference is "Transmission potential and severity of COVID-19 in South Korea"  International Journal of Infectious Diseases
Volume 93, April 2020, Pages 339-344