Hot Definition and 572 Threads

If a hot air balloon cools enough to start descending, does it keep accelerating until it hits the ground? Assume that the air inside does not cool off anymore, and pretend that the air pressure stays the same at all altitudes. I tried testing it by dropping a coin into a pool. It didn't seem...

Hi guys, I need help with heat transfer calculations The scenario is : Installing a coil around a hot pipe and extract the heat from the hot pipe to heat the fluid flowing through the coil. The whole assembly is insulated. I need methods/formulas to calculate the amount of heat transferred so...

I am looking for guidance on how to successfully measure vacuum using a device similar to a pirani gauge, my device however is a tungsten filament which is heated electrically to about 90*C, and it's current draw is a measure of vacuum.The problem I am having is how to relate specifically the...

A curious question that's come to my mind, as I'm doing a little research for game development, aiming for realism here. Assume you have a human corpse, not doused in any special kind of fuel, but wearing cotton/polyester clothing. And you set it alight, to slowly burn over time. I've heard of...

Dear PF Forum, Thanks for helping me so far. Lately, I've been reading Universe from nothing and quantum fluctuation. Those are very interesting topics. And I'd like to know more about them. And how the energy of the universe is zero. But before I would study them, there are things that...

I had a bit of rattle about this here before but I hope you folks ain't fed up with me yet.:) So after some trial and error I've built a working smps for my amplifier , it's pretty high power ,when testing dummy loads i got up to 2KW , since I don't need more for my project I never went further...

Homework Statement To research the physics of how a hot air balloon works. Homework EquationsThe Attempt at a Solution I just would like someone to check the main points I am going to include. The air inside the balloon is less dense because it is heated so that particles of air are further...

Consider a piece of pure Fe hot enough to have a bright white color (about 2 000 ºC, e.g.) and the characteristic yellow narrow yellow emission of the Na atom. Does the Na yellow band will be present at the thermal spectra of the pure Fe? My guess: Yes.

Natural convection always occurs opposite of gravity due to buoyancy; but I am confused as ice is solid so how could possibly convection even contribute to the heat transfer. I doubt about air movements nearby block that may contribute to greater heat transfer rate in case of hot block placed...

My textbook says - When a hot liquid is mixed with a cold liquid, the temperature of the mixture - "is undefined for some time and then becomes nearly constant". Shouldn't the temperature first decrease and then become constant ? Why does it say "undefined" ?

I have an electric fan that looks like this: Recently, when I flip the switch, the fan blades won't start spinning without any initial assistance. I have to manually push the blades to get them going. But this is not due to too much friction, the friction is the same. When I flip the switch...

Downloads are approaching 300,000 so somebody is interested. The 'planet', if it exists, is expected to have an 'appreciably eccentric' orbit. Is there any inventory of how many teams might be searching for this object?? EVIDENCE FOR A DISTANT GIANT PLANET IN THE SOLAR SYSTEM Konstantin...

I've read that H2O has an absorption/emission band around to 10 micron range. What conditions are required for photons of this wavelength to be emitted by H20 gas? In particular, how hot would the gas have to be? What amount of pressure is required? Under everyday conditions (like steam possible...

I was thinking about the concept of Unification at extreme energies, and how the symmetry breaking / condensation as a result of universal expansion resolves the necessary fields for our universe. As such, it stands to reason to consider a Hot Big Bang as candidate for the arena to allow for the...

Homework Statement Some hot air balloonists find themselves accelerating downward with acceleration a at a moment when the mass of the balloon plus the passengers and cargo is M. They want to accelerate upwards at the same rate, so they toss out some of the cargo mass m (and maybe one or...

If E=mc^2, why is hot air lighter than cold air? Hot air has more energy and should thus have greater mass and therefore be heavier as weight = mg

Suppose we have an insulated cylindrical container with a piston inserted from one end. Suppose the volume confined by the piston is full of a hot gas. Now let the gas drive the piston so that the volume is increased. Did the entropy of the system decrease because some of the energy of the...

I am building a nozzle for my hot glue gun, and it has made me realize that my math skills have become quite rusty. My goal is to figure out how fast I can extrude a hot glue stick through nozzle of different lengths. My assumption is that the longer the nozzle is (assuming I keep it at...

An ideal Carnot engine is composed of two reservoirs and a working fluid. The hot Reservoir and the cold one have temperatures ##T_1## and ##T_2## respectively, with ##T_1>T_2##. The working fluid is in a phase transition and has temperature ##T_1## at the start of the Carnot cycle. It undergoes...

Homework Statement A student investigates how the resistance of a thermistor varies with temperature. Student immerses a thermistor into a 50 degrees Celsius beaker of water and measures the resistance on an ohmmeter as the water cools. Student adds ice to achieve lower temperatures. Q1. The...

inb4 "google it", I did. There aren't a lot of information about this topic. Can a Hot Water Rocket or a Steam rocket ever succeed to reach outer space? I can calculate the exhaust velocity by determining the change in enthalpy I guess but I don't in which state will it exist in and how can I...

Hi everyone, So one of my students has asked me a question which I'm not sure how to answer. The question is: Why does the wire that supplies current to the filament lamp in a light bulb not heat up, even though the filament itself does? Please let me know your thoughts! Thank you :)

I'm a bit confused as to how only one wire changes it's polarity in an alternating circuit. I also checked out a previous thread (https://www.physicsforums.com/threads/how-can-polarity-of-ac-inverse-but-keep-the-live-hot-and-neutral-cold.752605/) and didn't find a sufficient answer. I found this...

Homework Statement Hot magma (1500 K) is flowing into the Earth at rates of 0.05 meters/year, 0.5 meters per years and 1 meter per year. Although more total volume of magma will retain a temperature at or above 1150 K at higher rates of flow for any given time (say, at 1000 years), a higher...

I am currently designing a whole-core for small PWR. I am calculating core life (years) vs. FdH and RFF. What is the difference between "Enthalpy rise hot channel factor (FdH)" and "Radial form factor (RFF)"? I have calculated "CHANNEL FDH" which is same as "RFF". Do I have to try "CHANNEL...

Ok, I've built a numerical model to show the cooling of hot magma sills entered into the crust over time. The results show that the volume of the "hot" zone when the emplacement of a constant volume of hot sills is all done will vary as a matter of two things: the overall rate at which the magma...

Interesting new study out http://www.telegraph.co.uk/news/science/science-news/10420496/Have-scientists-worked-out-why-hot-water-freezes-faster-than-cold-water.html Here is the paper http://www.nature.com/srep/2013/131021/srep03005/full/srep03005.html

Kolb&Turner in "the early universe" mentioned that for a scalar field ##\phi## at finite temperature, ##p=-V_T(\phi)## and ##\rho=-p+T\frac{d p(T)}{d T}## where ##V_T## is potential energy including temperature correction. My question is: when we consider the evolution of the universe using...

Hi, I'll describe my problem more specific. I have a continuous flow of this polymer thread (polystyrene) at 465 °K (190°C sorry I'm metric) that needs cooling down. It passes trough a water bath which is kept at 310°K (35°C). Now i try to calculate the heat exchange into the water, to...

Because a hot object like a hot metal has a lot of heat flowing through them are they charged? What are some ways to charge objects.

Does the kinetic energy of molecules make us feel a substance to be hot? I want to know the mechanism through which we feel something to be hot. How the molecules come in contact to our skin molecules and interact with them to send message to our brain through neurons? How the brain atoms...

Homework Statement "Using the above calorimetre with 100.0 g of water of in it at 20.0°C, a 50.00 g sample of a metal at 100.0°C is added. The temperature of the calorimetre rises to 27.2°C. What is the specific heat? (S.H. = 0.20 cal/g°C)" Homework Equations Heat capacity of calorimetre used...

I just sat with a cup of tea, and started wondering about this. If the cup just sits there, the tea will cool slowly. Will it cool faster if I repeatedly clench and let go of the cup? The difference between the cup surface temp and the surrounding air is higher than than between the cup and my...

How hot is Quantum Biology these days? Is there much research being done on this subject ?

How can this be done? So there is a container with hot water, and it's highly pressurized. It also has an output potential with a pressure reducing valve. I'm trying to workout how to feed the pressurized container with colder water (to refill). My first thought was that maybe when pressure...

I'm looking for a way to create pressure something similar to a teapot becoming heated and expelling vapor pressure. I want to find a way make a pipe or something to create a force so The pressure can push a fan hooked up to an alternator that will then store energy in big battery(maybe car...

Greetings !New to the forums. Here expanding my concept of what AC Electricity is My question (correct me if wrong).. If AC power alternates between +,- at a rate of 60Hertz/second and negative is used as -earth- at the AC generator If the hot wire touches the ground would happen? (I think...

I am currently working on thermal-hydraulics of a small PWR. The configurations are: Thermal power (MWth) 333 Core height is 1.8 m Pressure (MPa) 15.5 Total rod diameter (mm) 9.50 pin pitch (mm) 12.65 Pitch/diameter ratio 1.33 Flow Area (m2) 8.92E-05 Intlet mass flow/area (kg/m2/s)...

Homework Statement Consider photons crossing a large hot ionised hydrogen region with constant electron density ne = 5*105 m-3. Assuming that the photons and the electrons interact via Thomson scattering (with Thomson scattering cross section, σT = 6.65*10-29 m2, what is the thickness Δx that...

Just stumbled across this on my favorite site Dark Roasted Blend: I did not know there was an 'absolute hot'. (it's too large to post here) http://i.imgur.com/iHW7Dwh.png

I am planning in making a boiling tube that heats up to about 200c without a flame. I was thinking a coil of wire and a 9v battery (portable is always better). How would I make the wire hot - 200c/300c with only a 9v battery.

I'm building an frame out of solid 5/8 inch thick aluminum square bars. this frame will be around a fire temps close to melting points but there will be insulation in make sure it won't melt. I was thinking about drilling holes in the free space of the aluminum to reduce it's weight and if you...

I think this is now a legitimate topic. If not, I apologize. I would like to hear comments on the paper "Why models run hot", discussed in this article. Do people on this forum agree that the IPCC models overestimate the amount of positive feedback in the Earth's climate system.? Or is this...

20 gauge copper wire is rated for 5 amps. Suppose someone use 18 gauge copper wire and wraps it 60 times around one side of a 1 inch iron ring, with the two ends then connected to a plug. A separate piece of copper wire wraps around the other side 20 times, and goes to a 13.3 Ohm resister. So...

What's a suitable Material of construction for equipment handling hot brine (NaCl) solutions? Temperature is max approx. 100 C. I'm conflicted if or not SS316 works? I looked up an old handbook and it reported a corrosion rate of 0.2 mm/year (@80 C) which seems not too bad to me. But I've...

As I know, when a string of solar cells connected in series, if one of the cell is shaded, it will be reverse bias due to current mismatch and the voltage can be very high, say, 20V. But in short circuit condition, the overall voltage should be zero, if other cells are in forward bias, how can...

Homework Statement X . . . . .Rope . . . . Bulb >>> Light -----> V Hot bulb is making rotation . Exist C + V ? Michelson Morley X1..............solar system Not exist C+V = only Source is making rotation around X1 ? X1 - far far point in space Homework Equations C = 300...

Hi, everyone! I have a question: if we quickly fill a cylinder with steam from one end and with hot air from another end, both at atmospheric pressure and equal volume, with hot air 4 times hotter than steam, and then immediately seal that cylinder -- will pressure change as steam and hot air...

From what I understand, the observable universe began as homogeneous and very hot. if the universe was very hot, doesn't that mean that particles are vibrating at very fast speeds? after all, isn't heat simply kinetic energy of particles? if this is the case, then how could the universe be...

I need create a math model to predict the temperature of a copper pipe with hot air flowing through based on the temperature of the air, properties of the air and copper, and the surface area of contact between the air and the pipe. The pipe will start cold but I will be looking to the...