Daft sciencey type questions

[seren]

???

I said "daft sciencey type questions", not all complicated stuff about numbers.

I meant more like:

How does the mosquito repellant DEET work? Or any repellant? Can mosquitoes smell it? Or does it feel nasty when they touch it? I ask because I am one of those unfortunate people who are particularly tasty to mosquitoes. I have found that I can cover just about everywhere in DEET or Odomos (a repellant cream you can buy in India; I think it's 15% DEET or something), but the square inch I do not cover- they find it and bite it. To the extent that I got bitten on my personals because it was the only bit that wasn't DEETed!

I'd have thought if it was smell they would be generally put off me, not able to locate a specific spot like...er...that.

[skbuncks]

DEET, or N,N-Diethyl-meta-toluamide, acts as a strong repellant to mosquitos via an unpleasant activation of their antennal sensilla. In other words the smell puts them off.
However it has an effective range of only about an inch so uprotected, er personal bits, are prime targets for a biting

skb

ETA: I too am a prime target. I was in Oz a few years ago and the best protection I found was a 20% DEET aerosol which you could basically cover your entire body with in under 5 seconds.
Another thing, which you may have noticed, is that DEET acts as a rather good solvent for various plastics and some synthetic fabrics. I found this out the hard way when my crand new divers watch dissolved.

[NorthernSoul]

The bodyshop has aerosols of insect rellent that are 50% DEET.

Anyway, I'll have a go.

What is heat?

Sound is vibration
Light is photons

So what is heat?

[Trinoc]

Sound is vibration
Light is photons

So what is heat?

Also vibrations. Like sound, only more so.

[Lord Muck oGentry]

My favourite from The Last Word:

Why do mirrors reverse left and right but not up and down?

They don't ( as Trinoc has already observed).

Stand in front of a mirror with a green ball in your right hand and a red ball in your left hand. Now draw the line from your green ball to the one in the mirror and do the same with the red balls. The lines don't cross. Neither do the lines from your head to the head in the mirror and from your feet to the feet in the mirror.

There is no reversal.

[Mulder]

There is no reversal.

So, are you saying that, if you take a photo of an object and it's mirror image then, they should look identical? Why do ambulances have backward writing on them?

[skbuncks]

.....sits back and awaits the impending semantics arguement over the word 'reversal'


skb

[Trinoc]

So, are you saying that, if you take a photo of an object and it's mirror image then, they should look identical? Why do ambulances have backward writing on them?

Ambulance writing looks reversed because you are, in effect, looking through it from behind.

When you look in a car mirror, how do you know the car behind is indicating to turn right? Because the indicator on your right is flashing, even though if you thought of the reflection as a real car it would appear to be indicating left.

As Lord Muck said, stand in front of a mirror. The reflection of your right hand is on your right (your right, not what you think is the right of the person in the mirror). The reflection of your left hand is on your left. The reflection of your head is at the top. The reflection of your feet is at the bottom. But ... the reflection of your chest is facing towards you when it ought to be facing away, and where you imagine the reflection of your back to be is facing away when it should be facing towards you. You have been inverted along a line at right angles to the surface of the mirror, which makes perfect sense. You have not been inverted left-right or top-bottom.

[Trinoc]

.....sits back and awaits the impending semantics arguement over the word 'reversal'

The problem lies not with the definition of "reversal", but with defining "left" and "right" by the usual conventions relative to the imaginary person in the mirror, rather than relative to the surroundings.

[Mulder]

The simple answer is that the image you see is a virtual one, where the rays from any object never intersect at a point. In effect, the virtual image forms behind the mirror, just as it appears.

[niggle]

The simple answer is that the image you see is a virtual one, where the rays from any object never intersect at a point. In effect, the virtual image forms behind the mirror, just as it appears.

I suspect you're probably right, and so's Trinoc: it's a psychological phenomenon not a physical one and even then it's largely down to difficulties describing it.

it was a pretty smart question for the young kid who asked it though I thought!

(not as smart as, "why is it that no matter what colour the soap is, the lather is always white?", but getting there!

[Trinoc]

not as smart as, "why is it that no matter what colour the soap is, the lather is always white?", but getting there!

Ah ... an opportunity for you to explain light scattering to the said kid ...

[seren]

Please explain about fire more!

[niggle]

Please explain about fire more!

If you light a candle in a spaceship in deep space, what direction does the flame go?

[Matt]

In a microgravity environment a candle flame streads out in all directions forming a sphere. No direction is up so there is no convection current to carry away the exhaust gasses it produces. This swiftly smothers the flame. To keep a candle flame alight under these conditions you must keep it moving relative to the air. So in answer to your question the flame trails behind the candle.