What is Cold air: Definition and 22 Discussions

A cold wave (known in some regions as a cold snap or cold spell) is a weather phenomenon that is distinguished by a cooling of the air. Specifically, as used by the U.S. National Weather Service, a cold wave is a rapid fall in temperature within a 24-hour period requiring substantially increased protection to agriculture, industry, commerce, and social activities. The precise criteria for a cold wave are the rate at which the temperature falls, and the minimum to which it falls. This minimum temperature is dependent on the geographical region and time of year.In the United States, a cold spell is defined as the national average high temperature dropping below 20 °F (−7 °C). A cold wave of sufficient magnitude and duration may be classified as a cold air outbreak (CAO).

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  1. S

    I Centrifugal separation into hot & cold air streams?

    I have been reading about the Ranke-Hilsch vortex tube. Details of the explanation tend to differ somewhat among different sources, but it got me thinking about the following thought experiment. Air enters a tube of about 0.5 x 4 cm cross section. It passes through a section that is channelized...
  2. S

    B Does warm air rise or does cold air sink?

    I have a friend and he complained that at school they are teaching that warm air rises. He said it's wrong. He said instead the cold air sinks. Is this true?
  3. V

    Use only a powerful fan without a compressor?

    Hello & Thanks, Is it possible to use only a powerful fan without a compressor to make very cold air ? Thanks
  4. Fanny Viksten

    Why does cold air seem to optically zoom in far-away objects?

    I have noticed that cold air makes far away objects, such as mountains, appear closer than they do in warm clear weather. Does anyone have an explanation for this?
  5. J

    Can cold air become water in a vacuum cylinder?

    can cold air become water in a vacuum cylinder?
  6. S

    Airflow Across a Persistent Cold Air Pool in a Basin

    This question is regarding the general fluid dynamics involving warm air advection aloft a persistent cold air pool in a small basin that is recessed in a horizontal planar surface. For scale, the basin has a compound parabolic shape, with a 30° viewing angle, a .146m radius at the base, a .292m...
  7. T

    I left a soda in the car and it still feels cold.

    After a cookout on Saturday, I left two cans of Coca-Cola in my bag. Around Monday morning which is almost two days later, when I left for school, the cans were still cold with moisture on it. The next day, I put another can of Coca-Cola in the car and only left it overnight to see what the...
  8. S

    Why is Hot Air Lighter than Cold Air?

    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
  9. J

    Does Cold air cause more Air Resistance?

    I know that Cold Air is more dense than the warm air, so for example: If a car was accelerating facing a hot air, it will face less air resistance. But if it was facing a Cold air, it will face more air resistance because the cold air contain more mass per volume for each particle. It will face...
  10. A

    Energy problem dealing with heat extracted from cold air

    Homework Statement A heat pump requires 385 W of electrical power to deliver heat to your house at a rate of 2410 J per second. How many joules of energy are extracted from the cold air outside each second? Homework Equations COP= Qc / W . This was the only equation I could find...
  11. Pengwuino

    Stoopid car Stop blowing cold air

    Stoopid car! Stop blowing cold air :( So, since this is a forum full of people who knows mechanics so I figure this is the perfect place to ask this question! giggle. My car has been a pain in the butt lately. The heater blows cold air until I get the car to go over about 3k rpm. When I say...
  12. A

    Uncovering the Truth: Why Does Water Become Vapor in Cold Air?

    https://www.youtube.com/watch?v=2-vJPOFwz5E I came across a lot of these videos and people say the water is ''vaporized''. I thought about this and why would water become vapor in cold conditions? Isn't it simply becoming snow? What would happen if she had thrown cold water into the air? I
  13. A

    Speed of Sound (warm air or cold air)

    Homework Statement I am so confused with speed of sound. would sound travel faster in cold or warm air? if you put mathmatical equation in, v= 331 + (0.59Tc) then it would travel faster in warm air. but another theory says that sound travels faster in denser medium and cold air is denser...
  14. richard583

    Tractive Force and Greater Cold Air Mass Movement

    - Hello. ... New to the site. Had been searching for "Physics" focused forums, with an attached meteorological element, and found this one.I've been looking into and investigating the "notion" that main "tractive" force *, might have a great deal to do with main and broader cold air mass both...
  15. C

    Explaining Refraction: Hot vs. Cold Air

    Ok i get that hotter air is less dense , but when light goes from hot air to colder air we are dealing with the same atoms it is just that the photon will have less collisions , why would the angle of re-emission change for the photon just because it is having less or more collisions in the...
  16. L

    Cool Air Tactics: Fan & Ice Cubes

    I am trying to figure out how to get cool air. Say, if I have a fan and ice cubes. Should the ice cubes be in front of the fan(air blowing at them) or back of the fan (fan sucking). When I did it, I couldn't feel the difference.
  17. N

    Does hot air require more work to compress than cold air?

    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...
  18. D

    Cold air vs hot air in turbochargers

    Okay so i have a project, and this is pretty basic physics but I'm kind of confused. so for those of you how a turbo work, please help me out here. okay so: pV = nKT in thermodynamics. so in a turbo, as air enters the compressor turbine, n and k stay constant correct? however as air enters the...
  19. J

    Oil Heater, Humididy, Heating Cold Air

    Hi I am living in a 2 bedroom house with base bord heaters but i have also purchesed 3 oil space heaters, my landlord since has givin me a bogus eviction notice because of to much humididiy in the air, his fault really for nothin ensuring propor ventalation when repairing the house but my...
  20. E

    Diesel engine & very cold air

    We are looking at placing a normally asspirated diesel engine in a few cold climate. The engineroom will normally be heated. When the engine runs there is a ventilation system that will start up and draw outside air and also expel air from the engine room to outside, this is necessary otherwise...
  21. R

    The Mystery of Cold Air Travel: Light vs. Heat

    How does cold air travel? Isn't it like me flashing darkness at your face? Because cold is the absence of heat as darkness is absence of light. It's like nothing traveling. I know it's confusing.:confused:
  22. daniel_i_l

    Why does cold air go to the bottom of the room?

    I was thinking to myself, why does cold air go to the bottom of the room and the hot air to the top? At first the answer looked simple, the cold air is "denser" than the hot air. But if you think about it, at the molecular level the only difference between hot air and cold air is that the...
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