Try this interesting activity along with me- squeeze your mouth such that it’s almost closed and blow air fast on your hand. Observe that its cold. Now open up your mouth and blow air slowly on your hand. Now it is hot air that you feel! But how did this happen? Let us find out.
Blowing Cold and Hot Air
You might remember countless experiences of people blowing on their hands on a chilly winter morning. This activity helps to keep their hands warm. When given something hot to drink, you blow over it to make it mildly hot. Does this mean you can blow hot and cold air from your mouth upon your wish? Not exactly.
The air from your mouth doesn’t become hot or cold. This means it does not have a different temperature. In fact, the air from your mouth always has the same temperature which cannot change according to your wish.
Now let’s do another interesting activity. Take a deep breath. Now place your hand on your mouth and start blowing. Move your hand away slowly while continuing to blow and notice the change. What did you observe? When the hand was close to your mouth it felt warm. However, as you moved your hand away, from the air falling on your hand it became cold. It’s time to understand all these experiments.
So What is Exactly Happening?
We have observed that if we blow fast from a small opening the air comes out cold. Whereas, if we blow slowly from a large opening the air is hot. Further, if we place our hand on our mouth, it feels warm, i.e. we feel hot air. Then again if we move it away, the air feels cold. Let’s understand what is happening here.
It has been already told that the air from our mouth is always of the same temperature. The answer is closer than it appears. It’s in our ambiance. The air in our surrounding is always cooler than the air from our lungs. When we blow air from our mouth, if it reaches to an object fast, then a lot of ambient air gets mixed with it.
The result is that the air falling on the object gets cold. Conversely, if the air from our mouth reaches the object slowly, it remains warm. If the object is far away from our mouth, then a lot of surrounding air mixes up, as a result of which it becomes cold. On the other hand, if the object is placed close to the mouth the air falls directly on the object, which is warm.
So now you know why we blow cold and hot and the phenomenon of cold air and hot air!
Solved Question for You
Q: When we use blanket why do we feel warm?
- Because the blanket is warm
- The blanket does not allow air to enter
- Because our body is warm
- None of the above
Answer: The correct answer is option “B”. Cold air carries body heat away, Blankets form a barrier between body heat and cold air. Hence the heat doesn’t transfer through the blankets as air will not flow through it.