Why do things that are far away look smaller?

I understand that there are such things as perspective, vanishing points and so on, but I don't understand how they work.

Could somebody possibly enlighten me?

Re soaps and detergents, that's also how I thought they work. However I was actually talking specifically about *antibacterial* soaps and detergents. The other day I was watching an episode of "House, M.D.", and at some point Dr. House started rambling about the irresponsible behaviour of doctors prescribing antibiotics at a patient's first sneeze, etc. In his rambling, I think he mentioned also antibacterial soaps and detergents. I did a quick google search today, and I found some articles focusing on the topic and on the ingredient "triclosan" in particular.

http://www.foxnews.com/story/0,2933,170188,00.html
http://www.telegraph.co.uk/news/main...7/nsoap117.xml
http://www.webmd.com/news/20070817/p...src=RSS_PUBLIC

I would nevertheless still like to hear Chemgoddess' opinion...

The term 'Anti-bacterial' just means that it kills bacteria. The mode of action depends upon what the anti-bacterial agent is. For some anti-bacterial compounds, such as triclosan, there is a possibility of developed resistance. But if the anti-bacterial component is ethanol or peroxides which kills the bacteria in a general manner, there isn't.

This may help:
http://www.youtube.com/watch?v=98hO97ky-sA

Ummmm. . . . . no.

psst.
Sell him some postage stamps to lick. He won't know until you're far away with the cash...

If you eat pasta and antipasta at the same time, what will happen?

The universe implodes.

The eye perceives the "subtended" angle, i.e. the angular degrees between the object's extremities at the eye's focal point. A large object far away, e.g. the sun, only is a small angle for the eye and is apparently small.

Ah, but by the Macaroni Uncertainty Principle, you could never actually eat them at the same time. Again, we see that nature saves itself.

Uncle pasta will kick your ass!

When you look at a cow far away, you say that it looks small because the angle subtended by the cow at your eye is small (as opposed to the angle subtended when you're standing in front of it). In other words, what matters is its angular size.

All this works because as long as the distances involved are much greater than the typical wavelength of light, and as long as the medium in which light propagates is homogeneous (constant composition, pressure, temperature), then you can think of propagation of light in terms of "light rays" propagating in a straight line. You see the image as long as the light rays reach your eye.

A picture would make things a bit clearer, but I have no paint-like program on the machine I'm posting from.

[Edit: Whoops! I've been preceded...]

I wouldn't say the eye perceives the smaller angle. The fact that this angle is smaller for a farther object, as you correctly state, results in a smaller image being focussed on the retina.

Ah, Bistromathics.

I wouldn't want to sit next to you when you expel the fumes caused by the reaction that would take place in your stomach.

Ah! The rectilinear propagation of light! I remember now!

I must have been awake during those physics lessons after all...

Thanks for your replies. I think I've got it (but will have forgotten by the time I've polished off another bottle of prozacco...)

There is a plant that grows wild in Switzerland called Brennessel. The scientific name is urtica. It's called Nettle in english. It has stinging hairs that contain acid. It can cause a rash on skin contact.

Grandpa showed us that if one holds one's breath, the leaves can be grabbed without any stinging effect. We were amazed. We even tried it ourselves. Now how did that work?

The stingers work when you brush against the hair like trigger mechanism - if you grip a nettle leaf firmly you actually destroy the trigger. You could have kept on breathing as long as you grabbed the nettle firmly.

Ah, so it was just a trick. That's pretty of irresponsible of him to show us kids. I wouldn't want them to run through a field of nettles while holding their breath, thinking they won't get hurt.

Or maybe he doesn't know. I better warn him.

You should ask these guys at the 2007 Nettle eating championship in Dorset!