Why do firemen crawl in smoke filled rooms? plus 9 more videos..

Density - Why do firemen crawl in smoke filled rooms?
Sublimation - Why do mothballs disappear over time?
Ultrasound - Why is ultrasound used in sonar?
Refraction of Light - Why does a pencil look bent in water?
Stomata - Why do water lilies have stomata on the upper side of their leaves?
Frequency - Why do women have shriller voices than men?
Diffusion - Why can we smell hot food from a distance?
Density - Why does an iron nail float on mercury and sink in water?
Earthing - Why do buildings have lightning rods?
Rust - Why is oxalic acid used to remove rust stains?