106 votes
Accepted

Why don't you get burned by the wood benches in a sauna?

First of all, I hope you sit on a towel. But even when you touch wood with your bare skin, you don't get burned. This indeed has to do with thermal conductance. The point is not the heat transfer ...
  • 9,922
88 votes

Why do we need insulation material between two walls?

You can think of thermal conductivity as a measure of how readily heat will flow through the material while it is stationary. The low thermal conductivity of air means that it takes a long time for ...
  • 55.8k
76 votes
Accepted

Does anything in an incandescent bulb actually reach its color temperature (say 2700 K)?

Does any component in an incandescent lightbulb actually reach temperatures in the thousands of degrees? Yes, the filament. This is why the filaments are made of tungsten, which has a melting point ...
  • 1,892
48 votes

Why are steel thermal mugs much better than plastic ones?

Note that double-wall plastic cups aren't strong enough to withstand a vacuum and so they usually just contain a thin layer of air in which convection currents (absent in the case of the vacuum) can ...
48 votes

Why do we need insulation material between two walls?

If the air gap between the walls is wider than approximately 0.5 inches, the warm wall will heat the air, causing it to rise. The cold wall will cool the air, causing it to fall. This will set up a ...
  • 11.5k
41 votes

Why does holding a hot object with a cloth make it feel less hot?

Your body’s circulatory system is removing heat from your hand inside the oven mitt. This makes your whole body act as a radiator to dissipate the slight temperature increase in your hand and keep ...
  • 510
36 votes

Why are steel thermal mugs much better than plastic ones?

There is a reason steel is better for thermos flasks than plastic: lower emissivity. The way a thermos flask works is that it has two walls ideally separated by vacuum. Heat passes between them as ...
31 votes
Accepted

Why does water feel cooler than air?

Firstly, to make a valid comparison between how water and air 'feels' on your skin, two conditions would need to be met: Both water and air would have to be at exactly the same temperature. That ...
  • 34.6k
29 votes

Why is the ground warm during winter and vice-versa?

So there are two different things here. Shallow geothermal cooling The first is your animation from “Colorado Geothermal Drilling”. This is a long thin hole that goes maybe 100 meters into the ground ...
  • 35.6k
21 votes
Accepted

What causes contact resistance?

Another term is thermal resistance, This is incorrect. Thermal resistance is something that prevents heat flow. It is an entirely separate concept from electrical resistance. How is contact ...
  • 23.9k
21 votes

Why does holding a hot object with a cloth make it feel less hot?

I'm not entirely convinced you will be holding the pan long enough for the mitts to actually reach the same temperature as the pan, and I'm not sure you could hold it indefinitely, but let's ignore ...
  • 53.9k
19 votes

Why don't you get burned by the wood benches in a sauna?

Wood is full of air, and air is a terrible conductor of heat. It's not as complicated as it sounds, lighter, i.e. less dense woods, translate heat more poorly than dense ones. If you look at a cross-...
  • 191
17 votes

Why is the ground warm during winter and vice-versa?

The answer is that the ground has thermal inertia and it takes time for the variation in surface temperature to reach (attenuated) the deeper layers. This results in a phase shift between the seasonal ...
  • 409
16 votes

Can heat(?) flow from a cold object to hot object?

Heat is transferred from the spoon to the ice cream thereby reducing the internal energy and hence the temperature of the spoon. A metal spoon is more effective at this heat transfer than a wooden ...
  • 7,036
16 votes

Can you model cold as flowing?

If you were to model coldness conduction as a thing that flowed? ... If yes, are the equations and/or constants different, or is it just "add a minus sign"? "Add a minus sign" is ...
15 votes
Accepted

How much heating does Earth inner core provide to the surface?

Compared to the energy that the Earth's surface receives from the Sun, how much power comes from the inner melted core? Very little. The Earth's surface emits about 503 watts per square meter (398.2 ...
  • 39.6k
14 votes

Why does holding a hot object with a cloth make it feel less hot?

You can't "perpetually" hold a hot pan with oven mitts without burning your hand. The issue is how long it will take. Oven mitts enclose a lot of air, whose thermal conductivity is low, and ...
13 votes
Accepted

How can plasma torches reach $28000°\text{C}$?

You are probably confusing "temperature," which is proportional to the log(number of available energy states), with "total energy," which depends on how many particles have a ...
11 votes
Accepted

Will heat flow by conduction oscillate until thermodynamic equilibrium is reached in a solid object?

You are mistaken. You seem to be assuming that there is some kind of inertia in the process of heat transfer, as in water sloshing about in a tank. There is no such inertia here, so there is no ...
  • 26.6k
11 votes
Accepted

Can heat(?) flow from a cold object to hot object?

Heat is energy transfer due solely to temperature difference. Heat "flows" naturally from higher to lower temperature. In order for heat to flow from low to high temperature (e.g. a ...
  • 58.4k
10 votes

Does anything in an incandescent bulb actually reach its color temperature (say 2700 K)?

The filament reaches that temperature and acts as a black-body radiator. There is a type of measuring instrument used to measure the temperature at incandescent temperatures- called an "optical ...
9 votes
Accepted

How can a material conduct heat but not electricity

Electricity needs charged particles (or quasi-particles) to conduct it. Heat can be conducted with almost any quasi-particle. Diamond is one of the best conductors of heat in existence, and it's ...
  • 1,522
9 votes
Accepted

Does the order in which I layer blankets matter?

Such a system is actually quite complex, and as any backpacker would know, what keeps you warm is the amount of dead air within the layers. Dead air is non-circulating air. If we ignore the dead air ...
  • 164
9 votes

Why does holding a hot object with a cloth make it feel less hot?

What a great question! You are asking a question about the subfield of transport phenomena and so it can be worthwhile to have some models. So the first thing is linear heat flow, when you make ...
  • 35.6k
9 votes
Accepted

A question about thermal conductivity and heat transfer

The sensation of something feeling "hot" is a function of the rate of heat transfer to the skin and the duration of the transfer. The product of the rate and duration of heat transfer is the ...
  • 58.4k
9 votes

Why do we need insulation material between two walls?

Complementing the excellent answers on convection; some heat can also transfer through radiation, if the internal surfaces of the two walls are not treated to counter this. Both the warm and the cold ...
9 votes

Why is the ground warm during winter and vice-versa?

Heat pumps don't actually require the source of thermal energy to be warm. You can run an air sourced heat pump to heat your house in the winter using energy extracted from the freezing cold air ...
  • 6,712
8 votes

Does adding cold water to evaporative air coolers actually produce colder air?

It depends on whether or not you are calculating cooling per unit time or cooling per unit water. Per unit water, you get (a little bit) more cooling. Besides the enthalpy of vaporization, you get a ...
  • 35.4k
7 votes
Accepted

Is sun a black body?

Here is the measured radiation from the sun It is fitted with a black body curve, at the top of the atmosphere (yellow) and even though it is evident that there are deviations from the theoretical ...
  • 225k

Only top scored, non community-wiki answers of a minimum length are eligible