Archimedes Principle - Why do we weigh less in water? Newton's Third Law of Motion - Why does a swimmer push the water backward? Convex Mirror - Why is a convex mirror used as a rear-view mirror? Heat - Why do woolen clothes keep us warm? Atmospheric Refraction - Why do stars seem higher than they actually are? Gravitational Force - Why do you weigh less on the moon? Pressure - Why is it difficult to cut with a blunt knife? Density - Why do firemen crawl in smoke filled rooms? Ultrasound - Why is ultrasound used in sonar? Refraction of Light - Why does a pencil look bent in water?