Chemical Forums
Specialty Chemistry Forums => Other Sciences Question Forum => Topic started by: gera19 on March 06, 2006, 08:23:53 AM
-
Tea with milk or Tea without milk cools faster?
Why people can walk on hot coals without scalding their feet?
wat is e difference between temp and heat?
-
Why people can walk on hot coals without scalding their feet?
I think that those people can "switch off" certain nerves and so they don't feel anything..or not so much maybe...but I don't know how this is possible.... :Confuzzled:
-
Tea with milk or Tea without milk cools faster?
I would think that tea without milk would cool faster because fats tend to be good insulators.
Why people can walk on hot coals without scalding their feet?
2 things, one is the type of wood used. Some woods tend to burn at a lower overall temperature. Another thing is a hell of a lot of nerve or speed. I ran across coals once. My uncle was talkin about it. I forget what kind of wood he said to use. He also told me part of it is scar tissue and just shear nerve. We decided to try it out and after burning the coals down, spreading them out, and then letting it cool for several minutes I ran across some coals. It was kind of hot.
wat is e difference between temp and heat?
Assuming 'e' is the, a teacher once told me to think about temperature as a measure of the amount of heat something has. Somebody here probably has a more scientific answer. Mine is just a generalization.
-
I would assume that whichever cup of tea starts off hotter will cool faster as the increased temperature differential will increase the cooling rate.
Now walking on hot coals. I don't really know how this works but if I had to guess I would think it had something to do with the Leidenfrost effect where water on the feet would become instantly vapourised and thus very unconductive of heat towards the rest of the foot. Am I right???
I have always thought that temperature was a measure of a substances kinetic energy and heat was a measure of a substances kinetic and potential energy.
-
Tea with milk or Tea without milk cools faster?
You must define border conditions. Hot tea with milk cools faster then warm tea without milk. Hot tea with milk cools faster then warm tea without milk.
Cooling speed (understood as speed of loosing heat) is directly proportional to the temperature difference between object and its surroundings. Then it depends on the heat conducting properties of the object - how fast the heat from inside can be transferred to the surface. In case of tea with or without milk differences are too small to be easily observed.
However, this question is usually asked in form "I have prepared a cup of tea, but I will be able to drink it in 10 minutes, once I will finish a phone call. If I want my tea to be as hot as possible, should I add milk now, or after ten minutes." And in this case answer is obvious.
wat is e difference between temp and heat?
Temperature is a property of matter, heat is a form of energy.
-
Why people can walk on hot coals without scalding their feet?
I believe that after long periods of training JUST so they can walk on coals, their feet become scared and callused and as a result harder to burn. Then I think they also use pain-deadening meditation and take advantage of nerve damage from such training to avoid pain.
wat is e difference between temp and heat?
Hmm... there seems to be a bit of discrepency here, but I believe that temperature is a measure of the average amount of thermal energy per volume in a substance while heat is the transfer of thermal energy.
-
Heat and Temperature. This is a tricky one for me to picture. So I think we agree that temperature is a measure of thermal or kinetic energy, so the more the molecules are moving around the higher the temperature (right?).
Now, bakegaku, you say that heat is the transfer of thermal energy and temperature is the measure of thermal energy, so what I don't understand is when a phase change occurs (water to steam) for example there is a transfer of energy (does it have to be thermal?) but no increase in temperature. So how can there be a transfer of themal energy but now measured increase in thermal energy?
So is heat simply the transfer of thermal energy? Or can something contain heat? I know if you "heat" a beaker of water you are transfering thermal energy to it, or increasing the kinetic energy of its molecules. Surely the total amount of "energy" contained in a beaker of water is more than just its thermal energy?
This makes my brain hurt, so can someone please elaborate, bakegaku maybe you can tell me more details?
-
what I don't understand is when a phase change occurs (water to steam) for example there is a transfer of energy (does it have to be thermal?) but no increase in temperature. So how can there be a transfer of themal energy but no measured increase in thermal energy?
I believe that is known as latent heat ;D
-
So latent heat is the transfer of thermal energy with no change in temperature? I am still not convinced that heat is simply the transfer of thermal energy. :)
-
I am still not convinced that heat is simply the transfer of thermal energy. :)
Good for you. Heat is not a process (transfer) involving energy but the energy itself.
Temperature is a property of matter. It can be defined either as Boltzmann did (connecting it with a mean kinetic energy of particles) or in a fenomenological way - if you connect two bodies and there is no heat transfer bewteen them - they have the same temperature. If there is an energy transfer - body that looses heat is hotter then receiver.
-
Good for you. Heat is not a process (transfer) involving energy but the energy itself.
Temperature is a property of matter. It can be defined either as Boltzmann did (connecting it with a mean kinetic energy of particles) or in a fenomenological way - if you connect two bodies and there is no heat transfer bewteen them - they have the same temperature. If there is an energy transfer - body that looses heat is hotter then receiver.
Yes, good this is what I thought. Thanks :)
So you can add heat to a substance and may or may not increase its temperature. This is when a substance has a change of state, for example.
-
I guess I interpreted the first question differently from mike and borek. There are many variables to take into affect. I wasn't think about milk being kept. I was assuming adding it to tea if it were the same temperature. One wouldn't do this though obviously. To answer the question better one would need to put more parameters on the question.
Like I said I ran across the coals briefly. Lasted not much more than a few seconds and it was pretty hot. I think people who truely walk across coals like bakegaku says, they have a lot of scar tissue under their feet and callus.
-
Yes, good this is what I thought. Thanks :)
So you can add heat to a substance and may or may not increase its temperature. This is when a substance has a change of state, for example.
Exactly! You can add or subtract heat from a substance, but you can't add or subtract temperature. Temperature is a measurement of heat.
-
Exactly! You can add or subtract heat from a substance, but you can't add or subtract temperature. Temperature is a measurement of heat.
Ok one last thing then. Does heat only refer to thermal/kinetic energy? And if you can add heat to a substance without raising its temperature what is that energy? Potential? Chemical?
What about this example: If you had some hot oil, that has a certain temperature right? So this hot oil possesses heat energy which it can transfer to something that is relatively cooler or at a lower temperature. Now if you were to ignite the oil it would release a whole lot more energy. So does heat energy refer to just the thermal energy that warm oil can transfer to a cooler substance or does it also take into account potential chemical energy etc? We can assume that temperature in this case can only refer to the thermal energy of the oil.
Thanks for your input guys :)
-
Ok here's one:
Does cold water or hot water reach boiling point sooner?
Also, which one will freeze faster?
-
Does cold water or hot water reach boiling point sooner?
I would say hot water ::)
Are you going to tell me this is a trick question?
-
Are you going to tell me this is a trick question?
Perhaps...ever hear of the Mpemba Effect? :)
-
Don't leave us hanging :D
So what is the Mpemba Effect? and how does it explain hot water freezing before cold water. or cold water boiling before hot water?
-
http://en.wikipedia.org/wiki/Mpemba_effect (http://en.wikipedia.org/wiki/Mpemba_effect)
-
Ok well from what I've googled, here are several factors:
Source: Some Univeristy Site (http://math.ucr.edu/home/baez/physics/General/hot_water.html)
1. Evaporation -- As the initially warmer water cools to the initial temperature of the initially cooler water, it may lose significant amounts of water to evaporation. The reduced mass will make it easier for the water to cool and freeze.
2. Dissolved Gasses -- Hot water can hold less dissolved gas than cold water, and large amounts of gas escape upon boiling. So the initially warmer water may have less dissolved gas than the initially cooler water. It has been speculated that this changes the properties of the water in some way, perhaps making it easier to develop convection currents (and thus making it easier to cool), or decreasing the amount of heat required to freeze a unit mass of water, or changing the boiling point.
3. Convection -- As the water cools it will eventually develop convection currents and a non-uniform temperature distribution. At most temperatures, density decreases with increasing temperature, and so the surface of the water will be warmer than the bottom -- this has been called a "hot top." Now if the water loses heat primarily through the surface, then water with a "hot top" will lose heat faster than we would expect based on its average temperature. When the initially warmer water has cooled to an average temperature the same as the initial temperature of the initially cooler water, it will have a "hot top", and thus its rate of cooling will be faster than the rate of cooling of the initially cooler water at the same average temperature.
4. Surroundings -- The initially warmer water may change the environment around it in some complex fashion, and thus affect the cooling process. For example, if the container is sitting on a layer of frost which conducts heat poorly, the hot water may melt that layer of frost, and thus establish a better cooling system in the long run.
Finally, supercooling may be important to the effect. Supercooling occurs when the water freezes not at 0° C, but at some lower temperature. One experiment found that the initially hot water would supercool less than the initially cold water. This would mean that the initially warmer water might freeze first because it would freeze at a higher temperature than the initially cooler water. If true, this would not fully explain the Mpemba effect, because we would still need to explain why initially warmer water supercools less than initially cooler water.
----
Confused? Me too. :D
-
This are my suggested answers:
The specific heat capacity of water is higher than that of milk. Translated to practical situations, it means that water retains heat much longer than milk. The definition of specific heat capacity expalins this fact.
There it is! Tea with milk has lesser water than tea without milk which is only water thro'out.
The same reasoning of sp. heat capacity of water can be used to expali walking on coal. Tissues are made up of mostly water....get the point? "Another thing is a hell of a lot of nerve or speed". :-))))
Also, before people walk on coal, they wet their feet for the very same reason that sp.heat capacity of water is very high....by the time they come out, the water on the surface of their feet would just have evaporated and they would not feel the heat of the coal.
=)
-
heat is the transfer of thermal energy.
I thought we decided this was not accurate. Otherwise heat doesn't exist unless it is being transfered
-
I thought we determined that heat was the energy being transferred, and not the process itself. I think Lily should've paraphrased it slightly instead of taking the ill-stated sentence directly from my post ::)