The wind makes you feel cold, but a fan blowing on a thermometer doesn't change it. How are we different?

Question

The wind certainly makes you feel cold. Yet a fan blowing on a thermometer does not change the reading! Even though both thermometers and people have red noses, they differ in the effect that the wind has. How could you discuss the other respects in which you differ from a thermometer that that might explain this?

Answer 1

it's because we generate our own heat. the fan makes us feel cool, because it helps to dissipate our body heat. since the thermometer doesn't generate heat, the fan doesn't cool it off.

also, we produce sweat. wind helps the sweat to evaporate, which cools us off because of the energy required for the water to change state from liquid to gas. the thermometer, of course, doesn't sweat.

Answer 2

There are two factors involved in this:

First factor is the removal of warm air surrounding us (we produce heat by metabolism) thus allowing further dissipation of heat. This is true in those places where the surrounding air temperature is less than the body temperature. Thus even in failry severe winter, we feel warm after a few minutes in the absence of a breeze because the air surrounding our bodies gets warmed up and acts as a blanket (air is a good insulator). The thermometer has no internal heat source and so reaches the temperature of the air in a few seconds and stays constant. Clinical thermometer cannot drop its temperature continuously since a small kink is provided in the mercury column to prevent the mercury falling back into the bulb when we take the thermometer out of the mouth. Thus it cannot reflect the change in temerature of the bulb. If we have a laboratory thermometer of 0 - 100 C, we can register a small change in the first few seconds.

The second factor is more dominanat and is more interesting.

Actually if the thermometer had a wet cloth wrapped around the bulb, it would register the effect of the fan by showing a lower temperture. What you are referring is the dry bulb temperature and yes, that is not affected. The difference between the two temperatures (wet bulb and dry bulb) is used to calculate the relative humidity of air.

We feel cold because of the cooling provided by evaporation of water. In very humid weather, this effect is seen to be much less. Water evaporation results in cooling since the latent heat of vaporisation needs to be extracted from the remaining water and thus cooling occurs.

You may notice the cooling when spirit is rubbed on your body (before an injection is given), even without a fan, because the alcohol evaporates much faster and thus cools the skin.

Answer 3

You radiate heat, so when there's no wind, you heat up the air around you. A thermometer doesn't do this. When the wind blows, it blows away all the air you've heated up.

Also, if it's warm out, you sweat (a thermometer also doesn't sweat). When the wind blows, the moisture evaporates faster, drawing heat from your body to change states. I bet if you poured water of the same temperature as the air onto a thermometer, then blew a fan on it, the temperature would drop.

Answer 4

When wind blows the body temperature is lost due to convection and we feel cold. This can be experienced when our body sweats. During wind blow sweat is evaporated , and for this process additional heat energy is utilised from our body and we feel extra cold. But as far as the thermometer is concerned no temperature is lost.

Answer 5

Just as a sidelight to the discussion, there is such a thing as a wet-bulb thermometer, which does get cooler when a fan blows on it, depending on the humidity. In fact that is one way humidity is measured.