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1
Perhaps the question is asking "Which will I hear more clearly: People walking around in the apartment above me, or the people walking around in the apartment below me?".

It depends on the floor construction, and whether carpet is installed, but I suggest that footsteps in the upstairs apartment will be more audible because:
- The vibration of steps in the apartment upstairs will be coupled directly into the floor upstairs, and will be conducted to the ceiling above your head, where a small amount of the energy will transfer into sound in your apartment. It is a small amount because of the considerable impedance mismatch between the air and the flooring material.
- The vibration of steps in the apartment downstairs will be coupled directly into the floor downstairs; a small amount of the energy will transfer into sound in the apartment below. A small fraction of this will couple into the floor below your apartment, and a small fraction of this will couple into the air of your apartment.

So I suggest that sound of footsteps from the apartment above you will be more audible than the sound of footsteps below you, as there is an extra barrier in the way of footsteps from the apartment below (all other things being equal).
2
Quote
fluoride.... I heard there was a thing called evidence
See the transcript at: http://www.abc.net.au/radionational/programs/healthreport/hotspots-of-health-inequality/7657824
The full report is here: http://grattan.edu.au/wp-content/uploads/2016/07/874-Perils-of-Place.pdf
          ...but it doesn't go into the detailed causes of dental problems...
3
A beam of sunlight in a dark room should reveal a good rainbow - after you adjust the prism to get a good angle.

There are also those "novelty glasses" that surround lights by rainbow streaks.
They use a diffraction grating to spread the light into a spectrum.
Just be careful not to look at the Sun with these, as the Sun is very bright.
4
The quality of a vacuum is a relative thing, and a temporary thing.

Although there may be no atoms in this cubic centimetre in this second, atoms are typically moving very quickly, so there probably will be an atom in that specific cubic centimetre, in the next few seconds or minutes.
5
 So, the definition of a vacuum is ''space devoid of matter'', which is straightforward.
However, to make a claim of a space without matter, you would have to say ''from point A to point B, there is no matter'' (or ''in between these end points there is no matter'' if you consider 3 dimensions).
Scientific papers say that there exists no vacuum in the universe because even in the most desolate parts of the universe there are about 3 atoms in a cubic meter. To me, this makes no sense and I drew this shitty illustration to help explain why: (EDIT: ignore the lack of a dimension here, this was kept basic just to show the point)



The green area (cubic meter) is clearly not vacuum. However, why isn't the blue area a perfect vacuum? Why isn't all the space in between these atoms considered vacuum?
Why would a cubic meter be used to show there is no vacuum since it is not a mathematically relevant unit? (As in, it is not a ''natural'' unit like the planck units)
Why couldn't I, following the same logic, say ''there are no atoms in this cubic centimeter of deep space; therefore, perfect vacuum exists.''?

Isn't then empty space/vacuum just equal to space? Isn't space/vacuum an entity through which particles and waves move and matter an entity off of which the same particles and waves bounce?
Doesn't any place in between matter/atoms possess the same properties as vacuum and why isn't it considered as such then?

I hope someone can clarify this; thanks for your answers in advance.
I am not a physicist or any kind of professional scientist but I wish to learn.

 

EDIT: I need to copy and paste this from another place where I wrote this for further clarification:

 

As I said, I'm not a physicist, but simply logically, the definition can't be exact.
Because the logic ''there is no perfect vacuum since there are ~3 atoms in a cubic meter even in the rarest parts of the universe'' is used to prove there is no vacuum, surely the statement ''there exists perfect vacuum since we know there are cubic centimeters in the universe which contain NO atoms'' must be just as valid because it uses the EXACT same logic, which absolutely nothing changed except for the unit of measurement.

You see what I mean? To state that there is or is no vacuum, you would have to state the end points between which are or aren't any particles. So why would you use a cubic meter to determine that? Why not the smallest possible unit you could use?

I guess the point of my statement is that I think it's ridiculous to state that there are no cubic meter-sized vacuums in the universe, because that has no relation to physics since it unnecessarily complicates the issue with scale.

I hope the question makes sense now.
6
Have you used sunlight and a prism?
Led and tungsten bulbs have a restricted spectrum.
7
Graham Cole asked the Naked Scientists:
   My grandson (Luke age 13) and I have being trying to create a colour spectrum but have met with only very limited success. We have prisms, multi led torches , single bulb torches. Black paper with slits and pinprick holes, dark room,  lit room, but cannot produce a satisfactory image. Can you suggest where we are going wrong or recommend a primer for this aspect of physics please?

Pleased excuse this naive query,

Thank you.

Graham and Luke
What do you think?
8
Well,as I have pointed out before, plenty of people deny the existence of chemtrails.
So your statement that "nobody denies chemtrails except you" is an obvious lie.

Plenty of people deny them.

Wishful thinking. A majority of people are actually afraid of chemtrails. The ones who is doing disinformation is people like you and the government.

Quote from: Bored chemist
So why are you accusing me of spreading disinformation: you are the one who is doing so- rather obviously.

Obviously, you don't understand the concept of disinformation.

Quote from: Bored chemist
And this statement
"Clandestine geoengineering activity is a fact that need no evidences to exist. "
makes it clear that you have abandoned science (and possibly rationality). You can hardly say that and also claim that I'm the one whose "wishful thinking doesn't promote scientific progress. "
If it existed there would be evidence.

No, I did not abandoned rationality; You just don't seem intelligent enough to use Google to search for chemtrails evidences yourself. Is that a rational attitude?

Quote from: Bored chemist
Nice pictures of clouds and contrails.

You have no clue what are composed theses "contrails". Nice disinformation.

Quote from: Bored chemist
Nobody has said that clouds and contrails don't exist.  Did you somehow think they meant something?

And re. "I suppose theses guys are unable to recognize a cloud..."
Well, apparently yes; they can't.
 It will be interesting to see what the court decides.

A contrail is not a chemtrail. This is a fact. Research for yourself before spreading disinformation on a science forum.

And yes, a fair trial of offenders of clandestine geoengineering activity is hoped.

9
If I recall correctly the international league table in Nobel Prizes was, at least until recently

1. USA

2. Trinity College, Cambridge

3. The rest of the UK

4. USSR

5. France

6. Rest of Europe and Israel

I think the breakup of the USSR may have advanced France a bit in recent years. Japan is strong late runner.

Normalised for population, Trinity College (population 1500) is in a different galaxy from the rest of the world.
10
Chemistry / Re: Can molasses remove rust?
« Last post by BigD on 29/07/2016 20:16:44 »
The reason I need to soak the entire block is that the lifters and consequently the cam are rusted in place.  The hope is that the rust will be loosened enough to allow their removal.  No amount of "elbow grease" is going to do that.  As for " I cannot imagine that putting an engine block in a tub of molasses could be a good idea" the block and cam and lifters are all just cast iron.  Posts on other forums describe soaking cast parts for months with no ill effects to the base metal.

What is getting lost here is that my original question was HOW DOES THE PROCESS WORK?.  Instead of answering my question I get advice on what I should be doing differently.  Unfortunately this is typical of many forum responses.
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