So. I've just graduated (I say just, I've been sitting on my arse for a good couple of months now), I'm currently looking into temp work and various bits and bobs so that I can earn some cash to go travelling without getting into anything career-like too soon. I had an idea recently to try out writing a science column - I did an essay based course at university last semester that I really enjoyed and did well in. I plan to write a few short columns and send them out to papers, see what happens.

I want to write about science topics that the average non-scientist person ocassionally thinks about. In the past my friends (mostly artists!) have asked me questions like why the sky is blue and basic relativity things (the twin paradox, etc). I was hoping some of you could think of some similar questions that I could then tackle. My degree is in physics, but I would be happy to research other science topics.

Thanks

why does the sun appear larger when it is setting?
why does the moon get those grooooovy shadows and eclipse sometimes?
why why whyyyy


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can I ask a more complex question dealing with relativity and the speed of light and stuff like that?

Help me sort out the Twin Paradox again. That part in Relativity ****ed my mind over.

If maeve can't answer them herself, I'm sure between the two of us we could...if two physics graduates (I could have graduated...staying on to do a combined BSc and Masters...) can't answer your questions then nobody here can...

Why does water freeze at the top first when hot water rises.

I've never heard of hot water rising. Are you sure your not thinking of hot AIR? I could be wrong of course.

yeah...I don't understand what you're asking. ice floats on water because the hydrogen bonds create a rigid structure which is less dense than liquid water.

I'll answer MBeggar's first as its pretty simple, hope you don't mind maeve, it was bugging me...

This has nothing to do with Physics and everything to do with a person's perspective, when objects sit on the horizon and we can see them at a distance we think they must be large as a result.

If you actually measured the size of the sun or moon during the day/night you wouldn't notice any change in its size, you may think it is getting bigger but it isn't.

The only effect that will occur as the Sun/Moon move through the sky is the same effect that causes the sky to appear blue during the day, Rayleigh scattering, as the sun moves closer to the horizon the light from it has to travel through more of the Earth's atmosphere, as the angle at which light is deflected is dependent upon the wavelength, certain colours will be deflected more. This scattering may have a slight effect on the percieved size of the sun/moon (due to a slight bluring) but in reality its size will not have changed.

anybody not understand?

exactly, thankyou, so ice freezes at the bottom and then flots because the ice is less dense than the warmer water at the top.

Isn't warmer water at the bottom due to the density differences? Or something, anyway... There's something about pressure and possibly density and probably temperature. I think. Christ, I need to go to bed.

Maeve did you do Space-Time and Gravity, can't remember, if not you might not know how to answer this one...unless you google it, or just download the notes....

I'm going to bed now so if it isn't answered by tomorrow I'll write a reply, its not too complicated...its all to do with frames of reference and planes of simultaneity...just takes a while to explain...might include some pic's to help.

it r all in the crystal structure yo

I know the answers to these but:

- Explain the shape of a rainbow (the explanation that kids are told isn't even an explanation at all, it's a cop-out)
- I'm fairly sure the moon's gravity on it's own isn't enough to cause the massive tidal changes that occur everyday, and twice. I read the proper explanation about tides somewhere, but I forgot it.
- Same deal for seasons, the tilt of the earth's axis is far less significant than the overall variation in distance from the sun due to elliptical orbit. so why does the tilt have far more of an effect on seasons? (again, most people are simply taught that in summer our tilt just puts us nearer to the sun)
- You could explain how most people's understanding of evolution is grossly simplified.

So basically, anything where people are taught explanations that in fact don't work at all.

Here's one for the average joe: Why is it we can travel to the moon, but I still can't put silverwear in a microwave?

You actually CAN put silverware in a microwave. And it'll be fine.

[QUOTE=- Tony -]Isn't warmer water at the bottom due to the density differences? Or something, anyway... There's something about pressure and possibly density and probably temperature. I think. Christ, I need to go to bed.[/QUOTE]
The deeper you go, the higher the pressure. That pressure has an effect on the freezing and melting point of water. You can make water boil at room temperature by sucking the air out. Likewise you can get water up past 100 C and still be liquid. That's actually what drives pressure cookers.

Because casting microwaves onto your spam is totally different than blasting a can of spam on a trajectory in outerspace.

Unlike CD's. ZZZAP

Why, if you take a glass of hot water and a glass of cold water, and put them in the freezer, does the hot water freeze first?

I've always wanted to know the answer to that one; could never find it.

.. You could have tried it yourself.
And the answer is yes. (Not always though, it CAN...)

maevie, could there be physical objects that we cannot concieve of, and therefor not percieve, that affect the physical world around us so much so that math for the big, and math for the small, cannot compute together, and will not compute together, until we can sense these objects thereby postponing a unified theory until we do so?

I am fairly sure it's the moon's gravity.



This one is actually easy. When the earth tilts so that the sun light hits on more of an angle, less light actually falls on a given area of land. Thus the equator, which is usually perpendicular to sun light waves, is usually the hottest. When you angle on the more polar parts of earth increases though, less light hits per square area. Less light hitting = less energy absorbed and thus it gets colder.



It's really not grossly simplified. Random changes over time, and those attributes that contribute to a lifeform's ability to reproduce are selected for.

[QUOTE=Darth Evad]maevie, could there be physical objects that we cannot concieve of, and therefor not percieve, that affect the physical world around us so much so that math for the big, and math for the small, cannot compute together, and will not compute together, until we can sense these objects thereby postponing a unified theory until we do so?[/QUOTE]

Enter metaphysics.

But that really has nothing to do with why ice floats, which is entirely due to the crystalline solid structure being lighter than the liquid.

Its The Density Is Smaller

I remember doing this in one of my tutorials. Everyone immediately said it's the moon's gravity, but as soon as you think about it, you realise that's totally wrong.
Firstly, as Detty said, the moon just isn't big enough to cause those changes. Secondly, the moon orbits the earth once every 28 days, so why would it cause twice daily tidal changes? It's the sun's gravitational effect on the earth, rotating on it's axis once a day, causing first the pull of the tides one way across the earth towards the sun, then the other way.

and if you and Bond are REALLY stuck, then I'm sure a physics drop-out like me could answer something.... like... the bulls&&t physics and mmmm. stuff.

if(getThingFlags(source) & 0x8){
  do her}
elseif(getThingFlags(source) & 0x4){
  do other babe}
else{
  do a dude}

You could explain how water of 4' Celsius is the 'heaviest'... (it has the highest density at that temperature), so when a pond freezes (0' Celsius), the fish in it survive because the water on the bottom will always be 4' Celsius, because water of that temperature is the heaviest and sits at the bottom.

Or... you could explain the concept of relativity by giving the example of the thrown watch. (The faster things move, the slower time goes for those objects, so theoretically, if you throw your watch across the room, it will be slightly behind on you in time. (So slightly that you probably can't even measure it, buts still....) There's the famous example of the watches of the astronauts who went to the moon. When they returned their watches were behind the exact amount of time Einstein had predicted.

It really is oversimplified i'm afraid, the original theory of evolution doesn't account for nearly enough of what actually happened.

Hate to do this maeve but your wrong...Prof Thompson explained this during one of the Synoptic Physics Lessons...

I'll admit that I couldn't remember the reason why its just the force of the moon and so I had to look it up, but now that I’ve read it, it makes perfect sense (again).

Let me first say why the Sun can't be the cause of one of the tides, have a quick look at any tidal chart/times, look at the difference it'll be ~12 hours and 25 minutes, as a day is very very very close to 24 hours long a tide due to the force of the sun would occur every 12 hours and eventually due to the out-of-sync nature of the tides and Earths rotation the two separate tides would come together at some point, which they don't.

Now onto the real reason.

Let me first say centrifugal force and for those of you who want to try and work the answer out for yourselves think about it.
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As you hopefully know if you were to stand in the centre of the Earth you would be weightless, however because of the moon this point is offset in the direction of the Moon and the Earth and Moon both rotate about this point together, I'll call it the rotation point.

With this rotation there comes a centrifugal force that acts upon the earth, and hence the water will be "pushed" away from this rotation point which will lie directly between the Earth and the Moon (just under the Earths crust...well a few 100km's below...), we now have our tide on the opposite side of the Earth to that of the Moon.

As for the side of the Earth that faces the moon, that tide is easy to explain as it is due to the gravitational pull of the Moon.

The sun does have an overall effect on the tides, but is small in comparison, but the Sun's role is an important one for the high and low tides during the year.

When the force of the Moon and Sun work together, i.e. you can draw a straight line from the centre of the moon, through the Earth to the Sun, then the two gravitational forces are working together and produce the high tide once a year. When the moon is at right angles in respect to a straight line from Earth to the Sun, the force of the moon is working against the Sun and we get the yearly low tide.

There are websites that go into slightly more detail than I just did,

http://www.thejump.net/sunset/whytides.htm

However do not go to here, its absolutely useless.

Hope that all made a bit of sense...I'll get onto the other questions later...I'll answer the twin paradox next...

What are Light Cones? are they like traffic cones?

i always wanted a Light Cone explained.

[QUOTE=James Bond]Hate to do this maeve but your wrong...Prof Thompson explained this during one of the Synoptic Physics Lessons...[/QUOTE]

meh...if you say so. I remember Jones telling us the opposite, but then... I didn't actually check my notes.

Why when salt is in water the water temperature can go below 32 degree's without freezing??

And why can you float better in salty water? Does the salt increase the density of the water or WHAT!!?!?!?!?!?

I'll just quickly explain a few terms I’ll be using for those of you who haven't taken any advanced physics course.

World-line = Imagine an object moving at a constant speed from an origin, if you were to plot its position on a distance-time graph, it would trace out a straight diagonal line from the origin, this diagonal line is its world-line. If the object undergoes an acceleration at any point during its journey a curve would appear in this line.

Frame of Reference = Imagine you are travelling in a car at constant speed, if you were to measure the speed of another car you passed by, you could only measure the difference in speed, i.e. if you were travelling at 70mph and the other car 60mph you would measure its speed as 10mph. However a person standing on the bank would measure the correct speed as 60mph. Therefore how we perceive the world is totally dependent upon the Frame of Reference we compare it too, in this case we take a person standing still in space.

I might use some other terms during the explanation, if anyone has any problems understanding what they mean, don't feel stupid and ask, I had to many times.

For those of you not aware of the twin paradox here is a quick re-cap from my notes, I'll include pictures.

"Consider two twins who start from the same place in space and head in the same direction, twin A experiences no acceleration and his world-line is therefore straight. Twin B, on the other hand accelerates away from twin A for a short period and then undergoes inertial (constant) motion. After a certain time twin B decelerates until they are approaching A again with the same velocity as that with which they were originally going away from A. Finally twin B decelerates until they are at rest with respect to A (going at the same speed). Twin B will now surprisingly find that they are now somewhat younger than twin A, if they were to repeat the experiment several times, travelling at the same speed each time, they would find that the relative amount by which twin A ages is proportional to the length of Twin B's journey."

See below pic for a better idea.



Funny eh? its been proven with atomic clocks on placed on Jets that were flown round the world and then compared with those that stayed on Earth.

People have argued that the you could equally take Twin B to be standing still while twin A travels away in the opposite direction, reverses and comes back in respect to twin B's frame of reference. The paradox occurs because looking at it this way there would be an asymmetry between the measurements of the two twins. Twin B would be younger having not moved.

However this argument falls down when we consider the effect of acceleration on the frames of reference, twin A's journey is inertial, in that they don't experience any acceleration, they travel at a constant speed all the time. However twin B will experience acceleration 3 times during their journey, this is more than just relative motion with respect to twin A, twin B will be able to detect the force of the acceleration on themselves even if they were unable to see A. The argument of the twin paradox breaks down here.

One way to look at this argument is by using 3 different observers and split the journey up between them, see below.



Using this approach we can look at the problem without having to consider acceleration which can often complicate matters.

Observer B is receding from A at a speed greater than that of A's, similarly, C is approaching A at the opposite speed of B. A and B met at event F and synchronise their clocks, B and C then intersect at event E where C synchronises their clock with that of B.

Then when C and A finally met at event G and they compare clocks the same difference in time will be measured as in the first case where twin B had experienced less time than that of A.

And that is the answer to the twin paradox.

I'm actually finding explaining this stuff to other people is helping me understand it a lot better...any problems let me know.

Why does RadioShack ask for your phone number when you buy batteries? That's the toughest of all.....


-KnightRider2000

[QUOTE=James Bond]lots of science stuff[/QUOTE]
Ahh so that's it. IIRC, my professor said something about the fact that twin B had to accelerate three times over the journey and that was the key. It's a lot clearer now. Much thanks to you. I'm saving this post.

simply put, yes.

as to why it alters the freezing point, its to do with the arrangement of the h2o molecules and how with salt in the mixture it changes.

this is more of a chemisty question, any takers?

From my understanding adding salt to water will make alter the shape of the water molecules making it more difficult for them to combine with the normal water molecules. Thus to give them more chance of joining together you need to remove more heat to slow the molecules down giving them more time to join, I'm guessing when they do join the salt is removed from the water molecule.

I'm guessing someone else could probably explain that better.

[QUOTE=James Bond]simply put, yes.

as to why it alters the freezing point, its to do with the arrangement of the h2o molecules and how with salt in the mixture it changes.

this is more of a chemisty question, any takers?

From my understanding adding salt to water will make alter the shape of the water molecules making it more difficult for them to combine with the normal water molecules. Thus to give them more chance of joining together you need to remove more heat to slow the molecules down giving them more time to join, I'm guessing when they do join the salt is removed from the water molecule.

I'm guessing someone else could probably explain that better.[/QUOTE]

My chem teacher explained this a while back, but I can't remember. I think the fact that they bond makes it take a lot more heat for the water molecules to get up and goin.