Q: When you whistle out air on your palm held close to your mouth , the air feels cold , but when you blow out air from your mouth , keeping it wide open , the air feels hot . Why ?
Sol: When we whistle we blow out air through a small opening between the lips . This is adiabatic expansion , so there is a drop in temperature . When we keep our mouth open , hot air of the mouth is blown on the palm and so it feels hot .