There are many physical phenomena that can be modelled by sine waves:

Waves in water are an obvious example,

Compression and rarefaction in the propagation of sound,

Transmission of all electromagnetic radiation,

Vibrations of strings in musical instruments,

Bodies "bouncing" on a spring.

Also, more complicated motion can be modelled by a superposition of many sine waves (using Fourier transforms). This enables complex motions to be studied more easily.

Because in Africa...Blacks and Whites were separated. Whites had more power than Blacks...in the Springboks team then, there was only white players. Ofcourse some people didn't like this and protested.

Look it up on Wikipedia...Stupid -_- I learnt this when I was 10...how old are you?

Because older A/C systems were designed to use R-12 coolant and they do not run as efficiently using R-134. Manufacture of R-12 was banned in the US due to concerns over it's adverse effects on the ozone layer.

because they contain large amount of iron oxides

Because the Application is currently in BETA MODE. There is over 98 million questions on Wiki Answers