If we were to absorb all the incident light falling upon us

[LogicalAcid]

We would most likely grow in temperature greatly correct? I know this sounds to basic but the answer would help me very much.

Because if our body absorbs all of the visible spectrum except the part it reflects, why don't we grow very high in temperature?

 

[russ_watters]

We lose heat mostly via convection and evaporation so it balances out.

 

[LogicalAcid]

We lose heat mostly via convection and evaporation so it balances out.

I know, but then why does metal get much hotter left out than we do? I have a feeling its cause since it reflects so much of the incident radiation coming of it, we feel it through that.

 

[Fish4Fun]

Actually, various animals use different methods of maintaining body temperature. Humans use sweat, breath, clothing and shade (and, in modern times Air Conditioning ;-) ) to maintain body temperature.

There is slightly over 1kW of energy in 1m^2 of direct sunlight. If your mass is 100kg, and 80% of your body is water, it follows that you have 80 liters of water. 1kWh of heat energy will raise 80 liters of water ~10.75C. Depending on the ambient air temperature and relative humidity this heat may be lost or gained.

For instance if we have an 80 liter black bucket of water in direct sunlight: if it is -10C it will likely freeze solid even with the 1kWh heat input. If the air temp is 35C it may heat up to a few degrees above ambient if their is no wind. In general it is the ambient air temperature that affects changes in water temperature. This has a lot more to do with the properties of water and air than heat input by sunlight.

Water has a fairly high specific heat capacity, ~4.2J/gC while iron has a fairly low specific heat capacity ~0.44J/gC. This means that while 4.2 Joules of energy will only raise a gram of water 1C, the same 4.2 Joules will raise 1 gram of iron nearly 10C. In addition to this, iron is generally dark in color, meaning it absorbs more energy from sunlight than water which is a combination of reflective and translucent.

Hope that answers your question!

Fish

 

[Andy Resnick]

We would most likely grow in temperature greatly correct? I know this sounds to basic but the answer would help me very much.

Because if our body absorbs all of the visible spectrum except the part it reflects, why don't we grow very high in temperature?

A perfectly absorbing object placed outside, exposed to direct sunlight would absorb about 1 kW/m^2 of power, and would also emit 1 kW/m^2 of power. A blackbody emits this amount of power when it's temperature is about 360K, with a peak emission at about 8 microns.

So, absent any convective/conductive heat loss to the atmosphere, the object would heat up until it reached 360K (about 87 degrees C/ 188 degrees F), and then be in thermal equilibrium with solar radiation.

 

[Rap]

I know, but then why does metal get much hotter left out than we do? I have a feeling its cause since it reflects so much of the incident radiation coming of it, we feel it through that.

The light landing on your body is mostly turned into heat. But your body automatically does things to keep the same temperataure. If your skin is warm, blood will come to your skin and be cooled more than if your skin were cold. If it were cold, the blood vessels would contract, and stop your blood from being cooled.

Metal does not regulate its temperature the way your body does. Metal seems hotter or colder than you expect because it can hold a lot of heat. If you have a block of steel and a block of wood (both the same color, so they absorb the same amount of heat from the light), then both will be at the same temperature after a while, but if you touch the metal it will seem warmer than the wood. Thats because your fingers will cool down the wood much faster than the metal, and it will feel cooler. Your fingers don't tell you the temperature of what they TOUCH, they tell you what temperature they ARE. The metal will heat your fingers up much faster than the wood, and it will feel hotter.