Can anyone help with the perception of temperature difference?

In summary, the sensation of cold air when blowing air from a puckered mouth is due to the majority of the air coming from the surroundings rather than the warmer air from the body. The motion of the molecules in the air and the pressure generated by blowing are not significant factors in this sensation. This can be observed by holding a hand closer to the mouth while puckering and feeling warmer air, and holding a hand further away while exhaling with a widened mouth and feeling cooler air. This phenomenon is similar to wind or a breeze, as the air movement can cause a perception of temperature change due to the surrounding air being at a different temperature.
  • #1
llstanfield
27
0
For some reason I'm having a difficult time understanding the reason why air 'feels' cold when you tighten your lips and blow air from your body, yet it 'feels' hot as you exhale with a widened mouth.

Why is this so? The only reason why I'm having considerable difficulty is because I keep thinking of the motions of the molecules. If they are moving fast, the air should be hot right? I am a layman, and this question may seem simple, but I want to understand in detail as to why this is happening.

Is this particular phenomena similar to wind or a breeze? And how it feels cold? Can someone provide some insight on this? Thanks.
 
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  • #2
The cold air you feel is the air around your face that is pushed by the air coming out of your mouth. When you open your mouth you have a much greater amount of warm air coming out than when your lips are puckered, so you can feel the warm air.

Try this. Pucker your lips and put your hand right up to your lips and blow. You will be able to feel warm air.
 
  • #3
llstanfield said:
For some reason I'm having a difficult time understanding the reason why air 'feels' cold when you tighten your lips and blow air from your body, yet it 'feels' hot as you exhale with a widened mouth.
The air actually is warmer when you open your mouth wider. It's not just a feeling.

Why is this so? The only reason why I'm having considerable difficulty is because I keep thinking of the motions of the molecules. If they are moving fast, the air should be hot right? I am a layman, and this question may seem simple, but I want to understand in detail as to why this is happening.
Don't confuse the motion of the molecules with the motion of the air.

Think of a swarm of flying insects. These swarms frequently seem to hover over one point on the ground. When that happens, the insects are constantly moving around with high velocities, but the swarm itself isn't moving at all.

The same is true of the molecules in the air. At room temperature, the average air molecule is moving at about 450 meters per second, despite the fact that the air in the room is "at rest". The air isn't moving because all the molecules are moving in different directions, so the air as a whole doesn't go anywhere, just like the swarm of mosquitoes doesn't necessarily go anywhere even though the mosquitoes are whizzing around like crazy.

With the air molecules moving at 450 meters per second, how much difference do you think it makes that you blow them out of your mouth at an additional 1 meter per second? That does add some energy, but it is insignificant relative to the amount of heat already in the air. It has almost no effect on the temperature that you feel.

The explanation is actually quite simple. Air blown out of your wide-open mouth feels warm because it is at body temperature, which is warm. If you instead produce a narrow jet by pursing your lips, the air is cooler because most of the air in the jet comes from the surroundings instead of coming out of your mouth. (Note: there might also be a small adiabatic cooling effect as the air expands after leaving your mouth. This is, at best, responsible for a small part of the effect.)
 
  • #4
Okay, so you're saying that it has to do with the air around me? Is the lower pressure (generated by me blowing) causing the perception of cooler air then? I never considered the relationship between the air inside my body and the air around me.

In addition I did put my finger closer to my lips as I puckered and exhaled the air by the way, and it does indeed feel warmer! Thanks for that suggestion.

But perhaps, is there some principle behind this? Or any universal theory that explains this experience?

Thanks for your time.
 
  • #5
eigenperson said:
The explanation is actually quite simple. Air blown out of your wide-open mouth feels warm because it is at body temperature, which is warm. If you instead produce a narrow jet by pursing your lips, the air is cooler because most of the air in the jet comes from the surroundings instead of coming out of your mouth. (Note: there might also be a small adiabatic cooling effect as the air expands after leaving your mouth. This is, at best, responsible for a small part of the effect.)

Oh, now I think I understand. Thanks for your response. So in a general sense, it's because the air surrounding me is at a lower temperature than the air coming from my body..which has the "cooler" perception of temperature. Am I accurate in this response?

Wow, I never thought of that! Now it kind of makes sense. I actually conducted a little experiment to corroborate your explanation.

As I had my mouth widened, and exhaled, I had my hand held at a LARGER distance...and felt cool air! So perhaps you were right, that the molecular interactions are negligent when talking about a HUGE volume of the surrounding air. Thanks for helping me again.
 

Related to Can anyone help with the perception of temperature difference?

1. What factors affect our perception of temperature difference?

Our perception of temperature difference can be affected by a variety of factors, such as humidity, wind speed, clothing, and previous exposure to different temperatures.

2. Can our perception of temperature difference be influenced by our emotions?

Yes, our emotions can play a role in our perception of temperature difference. For example, if we are feeling anxious or stressed, we may perceive the temperature to be hotter than it actually is.

3. How does our body maintain a consistent perception of temperature difference?

Our body has a natural regulation system called homeostasis that helps us maintain a consistent perception of temperature difference. This includes processes such as sweating and shivering to regulate our body temperature.

4. Is there a difference between our perception of temperature difference and the actual temperature?

Yes, there can be a difference between our perception of temperature difference and the actual temperature. This is because our perception of temperature is subjective and can be influenced by external factors.

5. Can our perception of temperature difference change over time?

Yes, our perception of temperature difference can change over time. Our body can adapt to different temperatures, and our perception can also be influenced by our experiences and surroundings.

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