You will need:
- Mouth
- Hand
Figure out why your breath may sometimesblow hot and sometimes cold
with this experiment.
INSTRUCTIONS
- First, keep your hand 15 cm away from your mouth and blow onto your hand by keeping your mouth open.
- Keeping your hand at the same distance, purse your lips and blow out air again.
- Next, get your hand very close to your mouth and repeat the process, first by blowing air with your mouth open and then by pursing your
lips and blowing air. - Is there a difference in
temperature?
RESULT
When you keep your hand far, your breath will feel cold when you purse your lips. But when you open your mouth and blow out air, it will feel warm. However, when you keep your hand close, the temperature of your breath will feel warm. This is because when you keep your hand far from your mouth, and your lips pursed, the hot air from your mouth comes out in a narrow stream and gets entrained with the normal cooler air of the surroundings. Whereas when your mouth is open and you blow air, the warm air coming out from your mouth comes out in a gust and there is little entrainment that can take place. On the other hand, when you keep your hand close to your mouth, there isn’t any time for the warm air to blow out in order to entrain the cooler surrounding air, making the air feel warm on your hands.
