Hot Definition and 560 Threads

Old CRT tv's use vacuum tubes and they get hot, but how does the glass get hot when the inside is under a vacuum and therefore shouldn't transfer any heat?

I want to calculate the difference in temp between the bottom & top of a hot water tank, Presumably the height of the tank, the diameter, the actual temp and time would be the variables. I will assume no heat loss. The heat input would be at the base of the tank.

Hello everyone, Heat passes from high to low, molecules pass from area of high concentration to low concentration, pressure everything. I was wondering why this was the case. I mean I can think of it like a force reaching terminal velocity, but what about heat does it have a force?

This is a product that's supposed to do away with itchy, smelly chlorine and bromine. http://www.spamarvel.com/index.html" "...a unique formulation of natural enzymes, minerals and plant extracts and contains no chlorine, bromine or other harsh chemicals ... made with seaweed, lanolin...

Does anyone know where to find this steel? We've tried a bunch of suppliers and no one seems to carry it. Anyone know why? Steel, 4320 or 8620 Hot Rolled Grain Size 5-8 ASTM A29. Any help or direction would be great. Thanks, Scott

To compress the observable universe into the size of a grapefruit, it had to be devoid of all motion, and therefore all heat and energy. Why wasn’t the heavy hunk of matter the size of a grapefruit that preceded the “Big Bang” that created our observable universe cold and without energy...

Hi all Is it possible that a RADAR speed camera, (the type that bounces off the road and is reflected off the vehicle and then the doppler shift represents the vehicle speed) can be affected by a raise in surface temperatue on a very hot day(40 degrees C plus, poster is in Australia) I...

G'day This question may sound silly but believe it or not i can't seem to find the answer on the internet, What makes a hot object hot?

i have an observatory practical to do, and being in my first year of uni, we are given guidelines on what we need to do. the practical is on Cosmic Rays, and we will be taking two 15 minute exposures to record how many we get. now my question, there is a step in the practical where we have...

Hello, I'm new to this forum and I have a very important question about engineering design. I am currently working on my final project in my undergraduate study. The project that I am doing is about waste heat recovery design. My case study is a plant with a couple of ovens. The plan is to...

Homework Statement I'm trying to find the buoyant force on a hot air balloon. The mass of the displaced fluid is 2800 kg and the acceleration is that of gravity, (let's say 10 m/s^2). Homework Equations F=ma The Attempt at a Solution I think that you can just multiply these...

http://kwcamerica.com/-hansa/images/product/10_501_134_480.jpg Obviously, I am a newb here, so thanks for reading my (probably simplistic) question. I've done a bunch of searching of the forums and didn't see what I was after. We recently moved into our new construction house which is...

Hot can be cold, and cold can be hot... What ? Has anyone ever experienced http://www.wired.com/wiredscience/2007/10/the-bizarre-eff/" , "Ciguatoxin produces toxic effects by activation of voltage-dependent sodium channels, resulting in hyperexcitability, decreased conduction, and prolonged...

Why does a hot object emit Infra red light. How are photons are emitted from it?

This is a theoretical question about completing a circuit and trying to understand what a main panel ground rod does. The question is: Could you run just one hot wire (not in a conduit, but in free air) without an accompanying neutral to the lug of the bus bar in a main panel. The neutral...

Okey, simple question. As written in the title, I'm really not sure how this should work. Should hot air need more energy to compress than cold air, is it the other way around or is there no difference? This is asked because I need to find out if a physical system could work or not... Any...

It is better to take a hot or cold shower after a regular days work i.e. not after exercising? I personally enjoy very warm showers regardless of the season. I was just wondering if there are any health benefits to either.

Homework Statement A hot-air balloon achieves its buoyant lift by heating the air inside the balloon, which makes it less dense than the air outside. Suppose the volume of a balloon is 1900 m3 and the required lift is 2500 N (rough estimate of the weight of the equipment and passenger)...

So if you have a typical basketball "mens". http://en.wikipedia.org/wiki/Basketball_(ball ) so, my friends and I were in a hot tub and one brought in a basketball. They were pulling the basketball to the bottom of the hot tub and we noticed that it did not shoot out as high as when we...

This is a very random question. Why does most males prefer hot girls over cute girls (provided that they're both different type of looks)?

Hi, I have access to a hot spring. I was thinking it may be ideal to construct a small geothermal electric generation unit using the steam. Question is, if I have access to the hot spring, is this enough as a source to go ahead with a geothermal generating unit of say 100 kw - 200 kw, which is...

If I had two cups of hot water and put one in the fridge and left one on the table which one after 10 minutes would be cooler ? I have no idea and have been asked this question, thanks in advance for the answer.

What is the best way to move hot air? Would it be blowing air across the heat source (ex: wood stove) or suck the air away from the heat source? I use a wood stove to heat my home which works perfectly, but it occasionally gets too hot in the living room (where the wood stove is). I want to...

I have a 5-wire unipolar J835L. I have not been able to find a data sheet on it, but I have found this diagram: also, the motor has the following information printed on its label: Uni-Polar, Bi-Filar 120 Ohms 7.5° per step or 48 full steps per revolution JARL J835L PM 24P I have connected a...

Dear Experts,o:) I have recently soldered some diodes to maintain a constant voltage. This i learned from this nice forum. But when using it, the diode can become quite warm. My doubt is, when diodes become warm to touch, like about 60 degrees celsius , is it something wrong with the...

I was thinking, if time passage varies with speed would the speed of atoms random movement (temperature) affect time? For example, if the universe is expanding, as some predict, it will eventually reach a state where everything will reach very near to absolute zero, or maybe absolute zero. If it...

Like most people, when I need a recipe or cooking advice, I head straight to the Physics Forums. OK, so I'm on the hook for an office pot luck contribution next week. I'm going to make some kind of hot appetizer. My first idea was frozen mini pastry puff appetizers (from Trader Joes) but it...

I was just curious why does our cheeks get hot and red too :mad:, when we get (suppose very) tight slap:biggrin:? It's not a homework question and it's just a (stupid) observation . Well I would be very happy if anybody answers.:biggrin::-p (I don't know which subject this question is...

Imagine a closed container (full of air) that allowed sunlight or other heat inside the bottom half, but block or reflected this heat on the top half. Would this create a consant rotation of air being heated and going up, then cooling off and falling back down?

Homework Statement You would like to put a solar hot wate system on your roof, but you'r not sure it's feasible. A reference book on solar energy shows that the ground-level solar intensity in your city is 850 W/m2 for at least 5 hours a day throughout most of the year. Assuming that a...

I am working on a new 45kW centrifugal water pump, which is >70C at the roller bearing pedestal. I wonder what' s causing such high temperature. The vibration measured at the bearing pedestal is indeed very small. The pump seems to be well balanced and lubricated.

Homework Statement What is the magnitude of the acceleration of a rising hot-air balloon if the ratio of the air density outside the balloon to that inside is 1.25? Neglect the mass of the balloon fabric, the basket and it contents. I don't know how to do a rho so "p" will be rho for density...

I've seen much mention in websites of matt black surfaces being better emitters of infra red than shiny silver ones so if a matt black and shiny silver surface are heated to about 100 deg C the black one will cool down more quickly as a result of this! Doesn't Wien's law state that the amount of...

Homework Statement 175 cm3 of hot tea at 87°C are poured into a very thin paper cup with 80 g of crushed ice at 0°C. Calculate the final temperature of the "ice tea". (Hint: think about two processes: melting the ice into liquid and, maybe, warming the liquid.) Homework Equations...

I'm curious about about an upper limit of temperature at which water can no longer exist in a solid state even as pressure increases. There are "ice" phase states such as VII and X which are apparently solid up to 600K under pressures over 10^9 Pa. Phase X is called a "proton ordered" state. Is...

Hello, I'm running a couple of experiments in hot rolling and am in need of calculating the coefficient of friction during these experiments. All the equations I have found to calculate this during rolling all involve parameters like the roll bite angle which I am not sure how to calculate...

Homework Statement A hot-air balloon has just lifted off and is rising at the constant rate of 2.3 m/s. Suddenly one of the passengers realizes she has left her camera on the ground. A friend picks it up and tosses it straight upward with an initial speed of 12 m/s. If the passenger is 2.5m...

A hot air balloon has just lifted off and is rising at the constant rate of 1.30 m/s. Suddenly, one of the passengers realizes she has left her camera on the ground. A friend picks it up and tosses it straight upward with an initial speed of 9.40 m/s. If the passenger is 2.30 m above her friend...

I have a plastic Gatorade type bottle that I reuse. Between uses, I fill it with hot water and shake, and then empty it. Once I empty it, if I put the lid on and wait, the bottle eventually deforms and sucks in on itself. Then when I remove the lid it returns to normal. Why does it deform? Is...

Is it possible for me to heat water with some type of system that can use the heat trapped in my ceiling cavity? If so what would be the best way of doing this?

Please help me with this : 1) Water circulates throughout a house in a hotwater heating system. The water is pumped at a speed of .7 m/s through a 4 cm diameter pipe in the basement under a pressure of 3 atm. What is the pressure, to the nearest N/m^2, in a 2 cm pipe on the second floor 5...

I know a hot air balloon goes up because the density of the hot air inside is lower. But what about free air, not trapped in a balloon? You often see exactly the same explanation, hot air is less dense so it goes up, but this does not make any sense if you consider the fact that air is just a...

Homework Statement A hot body is brought into contact with a colder body until their temperatures are the same. Assume that no other bodies are around. 1.Is the heat lost by one body equal to the hear gained by the other? 2.Is the temp drop of one body equal to the temp increase of the...

Hi there, I have a tiny 48-QFN chip that I have to solder manually. The pin width of the chip is .28mm and the clearance of the pins is .22mm. The pins are totally under the chip and from side I can only see little metal indicating the positions of the pins, which makes it impossible to...

What are average high temperatures in the middle of the deserts during hot summer times? A sattelite has recorded a surface temperature of 71 Celcius (159 F) in Lut Desert in 2005, however no given date or season in 2005. How about temperatures above 1,5 m from the ground and in other hot...

So I have an LC circuit at resonance except the capacitor gets very hot. There is about ~2Amps AC going across it. The setup is: 2x 0.1uF capacitors in parallel ~304uH inductor the ESR of the cap is 0.56ohms and the resistance of the inductor is ~0.7ohms. I was looking for the...

There are situations when a water drop falls on a really hot metal surface and, instead of evaporating, it kinda bounces on the surface. Why?

Hey there. So we have an old home (1902) that is 3 stories. We currently have a tenant in our ground floor apartment. She just informed me that she is unable to get the hot water to come out of the bathroom sink tap. She could let it run and run and it will not get hot at the sink tap. Her...

What is the reason for paper getting stuck to a hot bowl when it is kept on paper for a certain period . I hve seen particularly that newspaper when placed under a hot bowl gets stuck to the bottom of bowl when the bowl is lifted ? I think the cohesive forces b/w the the two surfaces must...

Hi everyone I work for a very small company, which produces steel products. Predominately from one particular hot rolled steel profile. (1040 grade) We currently subcontract our hot rolling to small chinese operators :( I know... At this stage our volumes are not large enough to warrant...