Hot answers tagged heat
48
Ice cubes have three distinct cooling effects:
The cube, initially at sub-zero temperature, absorbs some heat to reach fusion point (0⁰C).
The cube absorbs more heat to switch phase: it takes some energy to turn 1 kg of ice at 0⁰C into 1 kg of liquid water at 0⁰C.
The water absorbs some heat to become warmer than 0⁰C.
The three effects occur more or less ...
29
This is a very interesting question with a very interesting answer. The key lies in the reason for the stretchiness of the rubber band.
Rubber is made of polymers (long chain molecules). When the elastic band is not stretched, these molecules are all tangled up with each other and have no particular direction to them, but when you stretch the elastic they ...
22
Yes, it's 11% hotter today than yesterday. Of the three temperature scales you discussed, only the Kelvin scale allows meaningful ratios to be calculated. Dividing two temperatures expressed in Celsius or Fahrenheit is simply a mistake. There are numerous physical examples where it makes sense to multiply or divide by a Kelvin temp, e.g., the ideal gas law ...
21
What a great question! And because anything that involves food is close to my heart I can answer with authority having done the experiments :-)
There's a simple answer, a more complex answer and even an unexpected answer! The simple answer is that if you just want to boil off water you should leave the lid off. If you try the experiment of putting a known ...
18
The reason being closer to a heat source makes you warmer is the inverse square law. Think of it this way: If you have a $1~\mathrm{m}^2$ piece of material facing the Sun and located at Mercury's orbit, it will be quite hot. What does the shadow of this square look like at Earth's orbit (about $2.5$ times further away than Mercury)? Well, it will be $2.5$ ...
11
Several points that need addressing:
The seasons are due to the tilt of the Earth, but not because of the atmosphere. When the sunlight is grazing the ground at a low angle the same amount of heating is spread over a larger area than when the sun is directly overhead, so the temperature drops. The atmosphere has a negligible effect on absorbing radiation ...
11
A fundamental principle of thermodynamics is that heat flows from warm places to cold ones, through either convection, conduction or radiation, and it will continue to do so until the temperature equalizes across the system.
The stones are colder than the whiskey when you put them in the glass, so as the system heads towards equilibrium, the whiskey gets ...
10
Two reasons:
the cheese has a higher specific heat capacity than the crust;
the cheese has a higher thermal conductivity than the crust.
When you cool a given weight of cheese or crust from the oven temperature to your mouth temperature, the amount of heat it gives up depends on its specific heat. So the cheese, with its high specific heat, gives up more ...
10
In order to build any thermal engine as envisioned by you, you need both a cold and a hot reservoir, such that heat can flow from the hot part to the cold part and the entropy doesn’t decrease while you’re making energy.
The efficiency of such a machine has an upper limit of $(T_{\textrm{hot}} - T_{\textrm{cold}})/T_{\textrm{cold}}$ (as given by the perfect ...
9
TL;DR: Whiskey stones work by absorbing heat from the whiskey in an attempt to reach thermal equilibrium1.
As Thomas mentioned, ice has three cooling effects:
Ice itself takes 2.11 kilojoules of heat per g to have its temperature increased by 1 degree (Celsius). This number is known as "specific heat capacity"
Ice takes 334 kilojoules of heat per kg at 0 ...
7
John's answer is a good one, I just wanted to add some equations and addition thought. Let me start here:
Heating is really only significant when you get a shock wave i.e. above the speed of sound.
The question asks specifically about a $200^{\circ} C$ increase in temperature in the atmosphere. This qualifies as "significant" heating, and the ...
6
The metal needs to be specified as a heavy metal, for Lithium, the answer is the opposite.
The heuristic is that every atom gives you 3R per mole specific heat (3k per atom). The reason is the equipartition theorem, which is reasonably accurate for solids at room temperature. The amount of energy at temperature T is $.5kT$ for each quadratic term in the ...
6
I think your question is perfectly fine, I don't think this forum is only for advanced research level questions.
Assuming you are not actually receiving small droplets of water, the air around the droplets is cooled by the water, which will then cool your skin. This is strongly accentuated by the fact the water create air currents.
While the effect you ...
6
You're assuming that the propellor speed is dominated by the bearing friction, while in practice it's dominated by the drag on the propellor as it moves through the air. Typically the propellor will rapidly accelerate to a steady speed at which the force from the rubber band matches the aerodynamic drag, then the propellor speed will slow as the band unwinds ...
6
You also could harm an iron pan, yes, but the chances to do so are much smaller.
If you add cold water to a hot pan, the temperature in the metal drops locally (where the water touches the metal) and since metal extend with heat, cooling them down contracts them.
So, the region that is cooled down by the cold water is contracted, which results in internal ...
6
The water vapor in the bathroom will condense preferentially on the coldest spots around the bathroom. When you wipe the mirror with a towel the water vapor readily condenses on it again because you have not changed the mirror temperature. When you use the hair dryer, the temperature of the mirror is now higher and the water vapor will prefer to condense ...
6
The identity $E=mc^2$ is a universal law of physics. It says that the mass – that can be interpreted as the conserved mass; inertial mass determining the resistance to acceleration; or gravitational mass determining the strength of the gravitational field – is equivalent to the energy, a conserved quantity that was originally defined as the sum of the ...
6
Once the core has solidifed it can no longer generate a magnetic field. There may be some frozen in field, but I would guess that the strength of the magnetic field with decrease as more and more of the core freezes, so any residual field is likely to be small. The core of Mars is thought to be frozen and it's magnetic field is negligable.
Anyhow, the main ...
6
We already store waste by combining it with molten glass. It doesn't take very much energy - obviously no more than making glass!
The main reason for not doing it is political, it cost a lot to make that plutonium and it might come in handy to build bombs one day - so we don't want to waste it by reprocessing it.
(We also have a small problem of persuading ...
5
Heat is not
caused by thermal energy being radiated from particles due to their energy
heat is the ramdomized (i.e. neglecting bulk flows) energy of motion in any material (including, for instance, photon gases).
Any vacuum that we can make or have access too includes a small amount of matter, and the temperature of that stuff can be measured. Not ...
5
When first coming into contact with the water, it is conduction. The skin feels the water colder than air because water is a better conductor of heat than air. So the skin cools faster in water than in air.
For longer intervals convection will enhance the effect bringing cooler water next to the skin and removing the water already heated by the skin.
The ...
5
I suspect this is a formidably difficult question to answer from first principles.
The cooling depends on the details of the air flow around your cylinder, and also on the temperature difference. An aeroplane flies at an altitude where the temperature is -50C, so the cooling is obviously going to be very different to say a baseball travelling at sea level. ...
5
Assuming
1, you live somewhere that is colder outside than in
2, the curtain has finite thermal resistance (ie some insulating value)
3, the curtain is close enough to the window to reduce convection
Then yes.
Try measuring the air temperature on the window side of the curtain, it should be lower than the room.
5
In this example both the systems are of the same type of particles (with two energy states) and same number of particles. Therefore thermal equilibrium is defined when energy is equally shared between the systems, but the particles are still not allowed to be exchanged. The particles, although of the same kind, are distinguished as being in system A or B. ...
5
Whiskey stones aren't necessarily designed to keep the drink cold, instead they are designed to allow flavor profiles to come out in the drink that might not be present at room temperature. Some whiskeys open up at a slightly cooler temperature and using stones allows you to experiment without diluting the flavor of the beverage. There are better math ...
5
Double the ammount of water does not need doulbe the ammount of time to heat, since while the energy needed is doubled indeed, losses due to vaporization and radiation from the kettle should be approximately constant.
You can plot the time needed for a given ammount of water to boil and try to fit a function into that. With two data points you can manage to ...
4
Fire is a plasma. There are two kinds of plasmas: hot plasmas relevant to astrophysics or fusion are indeed a mixture of totally ionized gas. In cold plasmas ( northen lights, Neon tubes,flamme) the ionization degree is less than one but the mixture typically exhibit collective behaviour and a zoo of waves one do not encounter in gases. The most famous is ...
4
Heat is the thermal motion of particles. Hot object's atoms vibrate more than cold object's atoms. Heat is transfered by 3 main ways:
Conduction: Heat flows from hot objects to cold objects. If you have an electric stove, the heat flows from the coils to the pan.
Convection: Heat flows by bulk motion of a fluid. If you heard "hot air rises" this is the ...
4
Toilet paper is made from cellulose and cellulose molecules contain many hydroxyl (-OH) groups. These groups have a strong dipole and interact strongly with water molecules, so toilet paper is hydrophilic. When you breathe on toilet paper the water vapour in your breath condenses on the cooler toilet paper, and because toilet paper is so hydrophilic the ...
4
The motion of molecules that is responsible for heat content in water is random motion; that is there are molecules moving in all directions. The directed motion that you are considering ( all molecules moving in the same direction) from the flowing water does possess kinetic energy, but it is not heat energy.
However, if the water flow encountered some ...
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