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Kamis, 07 Juni 2012

Heat in the Life

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               When we buy ice cream and eat it immediately, over time the ice cream will melt. Why is that? This is because the ice cream receives heat from the surrounding air, thus increasing its temperature and causing the ice cream melts. When we consider the electrical cables in the street seemed loose. Why the power cord is loose in the daytime? How the electric wires at night? Menegangnya slack and power cables because of the expansion. Is it heat?

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                Heat is often used in everyday life, for example, to boil the water we use the heat from the fire, changing the form of ice cubes into the water by heating (heating member). But what is the heat it?Heat term was first introduced by Antoine Laurent Lavoisier (1743 - 1794), a French chemist. According to him, the heat flow is a kind of substance, the substance that flows from one object to another object. Heat will flow from higher temperature object to a lower temperature object, if the two objects is mixed or come in contact. Heating unit at the time expressed in units of calories. One calorie is defined as:'Amount of heat required to heat one gram of water so that its temperature rose by 1 degree C'.
                 Different heating temperatures, where the temperature is a measure of the degree of hotness or coldness of a substance. Meanwhile, the heat is received or the amount of heat released by a substance. In general, heat is defined as the energy received or released by a substance that the substance is the temperature goes up or down or even change its form.Heat can change the temperature of a substance or objectIf we consider water to be cooked, at first the water was cold (low temperature).
                 Once given the heat energy coming from the stove, the water temperature increases so that the water gets hot. In the event it can be said that the water receives heat so the temperature rises. Conversely, when a substance is the temperature of heat release will go down. The amount of heat received or released by a substance is proportional to the mass of the substance, substances, heat, and increase or decrease the temperature of the substance.
Mathematically the relationship is defined:

Q = m c ΔT

Where:
Q = amount of heat received or disposed of (J)
m = mass of substance (kg)
c = specific heat of substances (J / kgoC)
ΔT = T - To = increase or decrease the temperature of the substance (C)
To = initial temperature of the substance (C)
T = final temperature of the substance (C)
The constant c in the formula above is the specific heat of substances.

                     Specific heat is the amount of heat required by 1 kg of a substance to raise the temperature of 1oC. C This value depends on the type of substance.When you mix hot water with cold water, which occurs in the mixture is water will feel warm to the touch. This is due to take off the heat and hot water heat cold water is acceptable. In other words, the incident occurred heat transfer from hot to cold water. After a state of balance, the water is not hot and not cold but warm.
                      That is, heat is removed with hot water heat received by the cold water. This principle became known as the principle of Black:

Q out = Q received

                      In everyday life, we often find the scene on the states of matter, such as ice turns into water when heated, the water is boiled into steam. Heat leads to changes in temperature, but also can change the states of matter.Changes in states of matter not only because of a substance to receive or absorb heat. But can also occur because of the heat release of a substance. Various kinds of changes in states of matter due to heat absorption and release are:Melts and freezesMelting is the change from solid to liquid form. In contrast to freeze is the change from liquid to solid form. When melting occurs the absorption of heat, whereas the release of heat when it freezes. A substance that are solid can be converted into liquid by heating the substance to the melting point.Evaporates and condenses Yawning is a change in the form of liquid into gas, condenses on the contrary is the change in the form of gas to liquid.
                     When evaporated, the substance absorbs heat, and vice versa when a substance condenses releasing heat.Sublimes. Sublime is the change in the form of solid to gas without passing through the liquid phase or vice versa from gas to solid. At the time of the solid to gas heat is absorbed, otherwise at the time of gas to solid heat is released. Examples of substances that can sublimate is camphor, iodine, and naphthalene.Heat transferHeat naturally moves from higher temperature object to a lower temperature object. There are three ways of heat transfer, namely conduction, convection, and radiation.
                     Heat transfer by conductionConduction or conduction heat transfer through a substance is without any movement of particles of the substance. For example, we heat the end of a metal in the flame, after a while you will feel the edge that we hold to be hot as well.It shows that the heat moves through the metal rod from the hot to the cooler side, but the particles of the metal does not come to move. In fact, there are objects that can conduct heat well, and some are bad. Objects that can conduct heat well are called conductors. For example: copper, iron, aluminum, and steel.
                    While the objects are difficult to conduct heat are called insulators. For example: glass, wood, plastic, and water.The solid is a conductor of heat better than liquids and gases, because the distance between the solid particles are closer than in liquids and gases, so that heat can be transferred faster. Of the many types of solids, which is best as a conductor is a metal, because metal has a lot of electrons that can move freely.Heat transfer by convectionConvection on the gas with convection in the liquid.
                     Convection on the gas, eg air occurs when warm air rises and cooler air falls. Convection heat transfer or flow through a substance is accompanied by the displacement of particles of that material. Heat transfer by convection can occur in liquids and gases. This is caused by differences in the density of the substance.Convection in liquid Heated water expands, so that its density decreases. Therefore, the density decreases, the water moves up.Convection in everyday lifeIn everyday life, to make the house comfortable and not stuffy, it made the house ventilation system so that a change of air.
                     Hot air in the house can move out through the vents and is replaced by cold air coming through the vents. Utilization of convection in life:For automobile cooling systemsHair dryerChimneyRefrigeratorHeat transfer by radiationTo dry wet clothes after washing, usually performed by them under the sun. Clothes can be dried by the sun produces heat which can evaporate the water that is in clothing. How is heat energy from the sun to the earth, but is located very far from the earth and between earth and sun there is a vacuum? Heat energy from the sun reaches the earth because of the sun's heat energy form of electromagnetic waves that can through a vacuum. Electromagnetic waves emitted by the sun is known as infrared radiation. Thus, the heat from the sun can be transferred by radiation.

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