Explain the difference between the two statements mentioned below:
Spilling water on skin surface on a hot day will cool the body temperature.
Spilling vegetable oil on skin surface on a hot day will not cool down the body temperature.
Strategy to Solve this Problem
The first step will be to discuss the temperature regulation mechanism of the human body. It will be followed by the cooling mechanisms adopted by the skin surface on a hot day to maintain the aforesaid body temperature. Next will be an overview of the inherent properties of water and vegetable oils. Finally, a correlation between the body mechanisms and cooling effects by water and oil will be set to draw a conclusive difference between the two effects.
First step: how does human body regulates temperature?
Human body temperature should fall in the range of 97oF to 100 oF while the surroundings are at a temperature range of 70 oF to 130 oF. Human body has got an excellent mechanism to maintain such a condition. In such a case the heat transfer mechanisms like conduction, radiation, convection and evaporation play the role. The temperature regulation is performed by the hormonal balances primarily via hypothalamus that is further under regulation of neural system of the body. When the skin temperature reaches 37oC, the body neurons transmit the signals to let the sweat initiate that increases its rate with the increasing temperature. Contrasting it, when the temperature of the body falls below 37oC, the sweating is not initiated and other mechanisms come to play to save the body heat.
Second Step: the cooling mechanisms adopted by the skin surface on a hot day
On a hot day, the surrounding temperature is more than the inherent body temperature. The mechanisms of convection, conduction and radiation tend to transfer the heat in the body rather than escaping it out of the human body. Thus, evaporation of sweat is the mechanism that comes into play to let the heat out of the body. This led the body to experience the cooling effect in a hot day due to high heat of vaporization of water i.e. ~580 calories per gram for the normal body temperatures. This exerts a cooling effect to maintain the thermal equilibrium.
Third Step: Inherent properties of water and vegetable oils
PROPERTIES OF WATER
Water is an essential element for life such that majorly plants and animals are buildup of 60% water. It is chemically constituted of two atoms of hydrogen with one atom of oxygen. Such a structure imparts the special chemical behavior of electrochemical nature to the H2O molecules. Water is an excellent universal solvent that can dissolve ample number of compounds due to the slight positive charge of hydrogen atoms paired with slight negative charge on oxygen atom. It has a neutral pH making it neither an acid nor a base. Along with this, it has a strong surface tension that aids in anatomical transport of minerals and nutrients in plants and animals.
Most important fact to consider here is that water is a good heat conductor in liquid form and has a high specific heat. It means that water can absorb enough amount of heat prior to getting hot itself and vice versa. This quality helps living organisms to maintain their body temperature.
PROPERTIES OF VEGETABLE OILS
Vegetable oils are obtained from the variety of oil containing vegetarian products like corn, soyabean, groundnut, etc. They are majorly composed of polyunsaturated fatty acids like linolenic acid and linoleic acid and therefore remain liquid at room temperatures. These fatty acids form essential dietary elements. Fats and oils are basically composed or triglycerides that comprises single glycerol unit with three fatty acid units. Due to this composition, they are mostly liquids at room temperature and have very low melting points. The features to be considered here are that oils are hydrophobic elements and do not dissolve in water. Along with this, oils are a very bad conductor of heat. Vegetables oils are commercially hydrogenated to alter their natural properties. Due to their efficacy, they are widely used as fuels in the form of biodiesel derived from seeds of oil producing plants.
Fourth Step: the difference in effects of water and vegetable oil spills on skin surface
Considering the properties of water and vegetable oil, as discussed above, it is evident that water has quick evaporating quality by absorbing large amounts of heat whereas, vegetable oil do not evaporate. The melting point of water is high and that of vegetable oil is low which clearly explains that the capacity of absorbing heat by water is higher than that of oil. When both these liquids are spilled over the skin on a hot day, the one evaporating swiftly will tend to leave a cooling effect. Water will surely evaporate quickly by absorbing the body heat that will create a cooling effect. In contrast, vegetable oil will not evaporate and will form a film over the skin that will not allow even the sweat to evaporate and hence create a hot effect on the skin. An oil spill on skin traps the air and prevents any air exchange between the skin and atmosphere.
In contrast, vegetable oils locks moisture of the skin due to its greasy nature and film forming property and despite using it in hot days, it can be used in cold days to prevent the skin from drying.