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There are two types of heat the body is adapted to, humid heat and dry heat, but the body adapts to both in similar ways. Humid heat is characterized by warmer temperatures with a high amount of water vapor in the air, while dry heat is characterized by warmer temperatures with little to no vapor, such as desert conditions.
Because people are more sensitive to some asymmetries than others, for example that of a warm ceiling versus that of hot and cold vertical surfaces, the limits depend on which surfaces are involved. The ceiling is not allowed to be more than +5 °C (9.0 °F) warmer, whereas a wall may be up to +23 °C (41 °F) warmer than the other surfaces. [1]
This increases heat production as respiration is an exothermic reaction in muscle cells. Shivering is more effective than exercise at producing heat because the animal (includes humans) remains still. This means that less heat is lost to the environment through convection. There are two types of shivering: low-intensity and high-intensity.
Water is a better conductor of heat than air, thus if clothes are damp — because of sweat, rain, or immersion — water replaces some or all of the air between the fibres of the clothing, causing thermal loss through conduction and/or evaporation. Thermal insulation is thus optimal with three layers of clothing:
Polyester-cotton blended clothing is more comfortable to wear in humid climates than polyester alone. [1]: 79 A heavy pair of jeans made of 100% cotton that weigh 14 oz (396.9 g) can be cut down to 11 oz (311.8 g), without compromising durability, by changing the composition to a blend of polyester 50% with cotton or nylon 20%. [12]
The opposite is also true: A Biot number greater than 0.1 (a "thermally thick" substance) indicates that one cannot make this assumption, and more complicated heat transfer equations for "transient heat conduction" will be required to describe the time-varying and non-spatially-uniform temperature field within the material body.
Alcoholic beverages do not make the entire body warmer. [381] Alcoholic drinks create the sensation of warmth because they cause blood vessels to dilate and stimulate nerve endings near the surface of the skin with an influx of warm blood.
Uhthoff's phenomenon (also known as Uhthoff's syndrome, [1] Uhthoff's sign, [1] and Uhthoff's symptom) is the worsening of neurologic symptoms in multiple sclerosis (MS) and other demyelinating diseases when the body is overheated. This may occur due to hot weather, exercise, fever, saunas, hot tubs, hot baths, and hot food and drink