HEAT Earth's original source of energy is our. The sun emits electro magnetic radiation in the form of rays, rays and light.

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1 HEAT Earth's original source of energy is our. The sun emits electro magnetic radiation in the form of rays, rays and light. of the energy from the sun is reflected directly back into space while is absorbed before being re emitted as long wave infrared radiation. Both the reflection and absorption are achieved through the atmosphere and clouds. WHAT IS HEAT? Heat refers to how fast the particles in a substance are moving. The rate of movement can be measured by. The an object, the faster the particles move. The an object, the slower the particles move. All particles will come to rest at 273 o C, known as. Heat Transfer is the movement of heat from one body to another (gas, liquid, solid, or combinations) by means of radiation, convection, or conduction. RADIATION Radiation can be observed on days. When you stand out in the sun, your face feels warm. The sunlight is absorbed by atoms in your face and warms your face, without warming the air around you. The energy from the sun that is absorbed by your face is called radiant energy or radiation. Radiation is the transfer of this heat energy by electromagnetic waves. Solar radiation mostly passes through the atmosphere and is absorbed by all objects, such as humans, trees, flowers, roads, etc. These objects will then warm up. Darker objects, such as asphalt roads, will absorb and warm faster than light coloured objects, which reflect more of the radiation back to space. 1

2 Radiation continued... The rate of heat transfer varies for each material and each type of transfer. Objects absorb radiation heat based on their atomic structure and the angle of the radiation more than their state or density. Colour is one good example of an objects atomic structure (black objects absorb visible light while white object this light this energy source.) Glass only absorbs ultraviolet radiation! Ice because of its composition will reflect almost all of the solar radiation. This is called the Albedo effect. CONDUCTION Conduction is the transfer of heat from one to another within a substance. This occurs mostly in solids but can also happen in liquids and gases. Imagine you are holding a metal pin between your fingers and you place this pin in a flame. The pin absorbs the energy from the flame and the molecules inside the pin begin to move (warmer temperature). These faster moving molecules cause adjoining molecules to move faster and will eventually cause the molecules in your fingers to move faster. The heat is now being transferred from the pin to your finger and your finger will heat up. Heat flows from warmer to colder regions, and will transfer quicker with greater temperature differences. The rate of heat transfer through conduction also depends on whether the substance is a good. 2

3 LG1 How Heat is Transferred in Water note.notebook CONVECTION Convection is the transfer of heat through the movement of a, such as water or air. This type of heat transfer can occur in liquids and gases because the particles move freely, making it possible to set up warm or cold. Examples include water, heating vents in a house, winds and ocean currents. Convection occurs naturally in the atmosphere on a warm, sunny day. As the earth's surface absorbs sunlight, certain portions of the surface absorb more than others. The earth's surface and the air near the surface heats unevenly. The warmest air expands, becomes less dense than the surrounding cooler air, and becomes buoyant and rises. These rising "bubbles" of warm air, calledthermals, act to transfer heat up into the atmosphere. Cooler, heavier air then flows toward the surface to replace the warm air that just rose. When the cooler air reaches the surface, it is warmed and it too eventually rises as a thermal. This circulation is referred to as aconvective circulation or thermal cell. Hand gliders take advantage of these thermals to stay afloat for hours. SUMMARY OF HEAT TRANSFER Conduction Hotter particles move faster and as they bump into their neighbouring particles the energy is spread, transferring the thermal energy. Convection Hotter particles that are free to move rise while cooler particles fall. A current of movement is then established. Radiation Electromagnetic radiation stimulates the movement of specific particles within an object. The best example is the use of a microwave oven which stimulates the motion of a water particles. 3

4 Applying these Principles to Water A. An excellent example of heat transfer in water is the heating of a backyard swimming pool with the use of a solar blanket. All 3 types of transfer apply. 1. Radiation The sun produces 3 types of radiation,,. The solar blanket is good at blocking one of these types. The other two types, pass through the blanket and heat the water mainly at the surface. The water particles start to move faster and the pool gets warmer. The pool is constantly giving off radiation but the solar blanket this type of radiation. As a result, the pool gets. 2. Conduction Conduction is not significant in liquids because, by their nature, the particles in liquids are free to. However, the water particles which touch the solar blanket will gain some heat due to these collisions. 3. Convection A temperature gradient is established in the pool as in lakes. The top of a lake is then the bottom. (Fish like to spend more time at the bottom of a lake because cold water contains oxygen!) In a pot on your stove, the warmer water particles are on the and these warmer particles, looking for more room to move will. This is referred to as a convection. In this convection current, the colder water particles near the top to replace the rising warmer particles. A more uniform temperature is established in a pot of heated water than a lake or pool. To improve the uniformity of the temperature in a pool, pushing the water are used! warmer current sink visible jets visible ultra violet infra red ultra violet warmer infra red move infra red blocks more bottom rise B. Unique Properties of Water i) Rate of Heating Water is capable of absorbing a great deal of energy. The rate at which heat is absorbed in liquid water is slower than any other substance (except ammonia). As a result, water requires more energy more energy than land, pavement, trees, the air, to raise its temperature by 1 o C. Based on the law of energy conservation, water will release the same amount of energy when it cools by 1 o C. As a result, large bodies of water require a great deal of time to absorbing a great deal of and they require a great deal of time to releasing this to surrounding objects. Large bodies of water are said to moderate the local climate. This means. ii) Water is a liquid on earth Water can regularly be found on earth in all 3 states. If the temperature is below, then water is in its solid form and is called. If the temperature is between and, then water is in its liquid form and is called. If the temperature is above then water is in its gaseous form and is called water vapour or. The average temperature on earth is approximately 14 o C so most of the water on earth is found in its form. iii) Density The density of a material does have an impact on how heat is transferred by conduction but this is only one method of heat transfer. Water's density provides a different significance. Liquid water is more dense than ice. When a lake cools ice will form on the because less dense objects. This insulates the water below the ice and prevents the entire lake from freezing. Although solutes such as salt do change the density of water, it only as a minimal effect on climate. Oceans on average are a 3.5% salt solution. Salt is used in the winter to aid in the melting of ice. A 10% salt solution is required to lower the freezing point to 6 o C. A 20% solution would lower it to 12 o C. surface heat liquid float cool 100 o C 0 o C 0 o C energy 100 o C energy steam 4

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