•Heat as a form of energy . Heatcan make things hot and we canuse heat to do work.•We feel hot when the Sunshines. This shows that the Sun isa source of heat energy and givesout heat. Most of the heat on theEarth comes from the Sun.
•Apart from the Sun, there are many other sourcesof heat. Heat can be produced in many ways.•Here are some activities to show possible heatsources.
Heat sources Activities •Rubbing or friction- •Rub your hands togetherrubbing two objects against for some time and then each other can produce hold them to your cheeks. heat. Your cheeks will feel warm, showing that heat can be produced by friction. Rubbing hands can produce heat
•Burning- when an •Burn a candle or a piece of object burns, it paper and put your hands aboveproduce a flame that it. Your hands will feel gives out heat. hot, showing that burning substances can produce heat. Burning substances can produce heat
•Electricity – when •Switch on the electric bulb for electric current flows some time and place your handsthrough a wire, heat is near the bulb. Your hands can produced. feel the heat coming out from the bulb. Electricity can produce heat
•Heat can also be produced by:a. Bending metal- bending a coat hanger or a wire back and forth several times can produce heat in the object.b. Chemical reaction – after mixing solid sodium hydroxide with water in a test tube, the test tube will get warm.c. Collision – when an iron nail is hit by a hammer several times, the hammer and the nail will get hot.
•Heat is a useful form of energy. We use heat to:a. Cooking foodb. Drying clothesc. Boiling waterd. Producing steam to generate electricitye. Food drying for reservationf. Providing warmth
•Heat is a form of energy. An object becomes hot when itabsorbs heat. Heat is measured in Joules (J).•Temperature measures how hot or cold an object is. Theunit of temperature is degree Celsius ( C) or Kelvin (K).Temperature can be measured with a thermometer.•Heat and temperature are different.•The table below shows the differences between heatand temperature.
Heat Temperature • A form of energy •The degree of hotness or coldness of a body •Heat can do work •Temperature cannot do work •Measured in Joule (J) •Measured in degree Celsius (C) or Kelvin (K)•Transfer from a hot area to a Increases when heated and cold area. decreases when cooled
•The amount of heat•Objects with the same contained in an objecttemperature contain the depends onsame amount of heat. a. The type of theThe higher the material that thetemperature of an object is made of.object, the larger the b. The mass or the sizeamount of heat of the objects, andcontained in it. c. The temperature of the object.
•Heat only travels from a hotter object (or place)to a cooler object (or place)•Heat has several interesting ways of travelling: It travel by three ways:a. By conduction through solidsb. By convection through liquids or gasesc. By radiation through vacuum
•The flow of heat energy through solids such as metalsis called conduction.•Heat energy uses molecules to help it to get around.•For example, when a pan is heated, the molecules atthe bottom of the pan start to vibrate energetically.They collide with their neighboring molecules andcause them to vibrate faster. The passing of the heatenergy from one molecule to the next continues. In thisway, heat energy travels through the pan and thenthrough the food in the pan.
•Heat can flow through a liquid or a gas becauseheated parts of the liquid gas move.•Warm air rising above a heater is an example.•The flow of heat that occurs when a warm liquidor gas moves is known as convection.
•The process where heat energy travels through anempty space or a vacuum is known as radiation.•An example of radiation is the transfer of heat fromthe Sun to the Earth through mostly empty space.Such a transfer cannot occur via convection orconduction, which requires the movement of materialfrom one place to another, or the collisions ofmolecules within a material.
•Some natural phenomena occur as a result ofheat flow.•Warming of the earth by the Suna. The Sun gives solar energy every day. During the day, the Earth’s surface is warmed up and during the night, this energy is radiated back into space as radiant heat energy.
b. A fraction of the solar energy that reaches the Earth is absorbed, causing evaporation of water from the oceans, the lakes, the lands and plants. Convection current carries the water vapour up to the atmosphere to form clouds, which will form rains and thunderstormsc. The warming of the Earth by the Sun can cause changes in the climatic conditions of the Earth and many natural phenomena such as land ad sea breezes, thunderstorms, hurricanes and so on.
a. The unequal heating or air over land and water will result in breezes near the shores.b. During the day, both land and sea are heated by the Sun. However, the land gets heated up faster than the sea. The air above the land surface heats up, expands and rises. It is lighter than the surroundings air. To replace the rising air, cooler air is drawn in from the surface of the sea. This is the sea breeze. It can offer a pleasant cooling effect on a hot afternoon.
c. At night, the land cools faster than the sea. Whenthis happens, the air over the warmer surface of seaheats up and rises, pulling in air from the cooler landsurface to replace it. This is the Land breeze.
•A building can be kept cool by having a goodventilation system, so that air circulation in thebuilding is ongoing. Hot air from the building flows outfrom the top and cool air can flow in from the bottom.•Most of the traditional houses are built withventilation holes at the base of the house and at thetop near the roof. Hot air inside the house will rise andflow out through the ventilation holes at the roof. Coolair will enter through the openings at the base of thehouse to replace the hot air. This produces a naturalconvection current inside the house.
•In modern buildings, the ventilation system is mademore effective by installing exhaust fans and extractorfans. Hot and humid air can be sucked out and replacedwith fresh and cool air.•Modern houses are equipped with fans and airconditioners to make the house cooler. Modernbuildings use centralized air conditioning system to coolthe whole buildings.•Insulation can also help to keep a building cool.Buildings with loft insulation, insulating cavity walls ordouble gazed windows are usually much cooler thanthose which are built without insulating materials.
•When material allow heat to pass through themrapidly, they are known as conductors. All metals aregood conductors of heat compared with othermaterials.•Other materials like- metals, liquids and gases that donot allow heat to pass through easily are known asbad conductors of heat or insulators.
Examples of the uses of heat conductors indaily life. Materials/ devises UsesCooking utensils •Cooking utensils such as saucepans, pots and kettles areInsert image usually made of aluminum or stainless steel.kettle •They conduct heat quickly and easily to the food as thus save fuels.
Electrical appliances •Electrical irons and hot plates are made of iron or stainlessInsert image steel that conducts heat well. •Heat sinks that are used iniron computers, disk drives and televisions as cooling fins are made of aluminumOthers •Radiator coils and cooling fins behind the refrigerator are made ofInsert image copper. •Soldering iron rods are made ofSoldering iron rods iron with copper tips.
Insulators are used in many applications wherewe want to minimize heat flow or heat loss. Materials/ devices UsesWood or plastics •Handles for cooking utensils, kettles, teapots, soldering iron rods and so on. •They protect our hands from the hot surfaces.Cork, asbestos sheets, tiles To prevent tabletops from being damages by hot kitchenware or objects.Sawdust To cover ice blocks to slow down the melting process.
Woolen blanket or cloth •Used to keep the body warm on cold days. The woolen blanket and the air layer trapped inside can prevent heat loss from the body.Fiberglass, expanded •Used as insulators in the walls of icepolystyrene foam boxes and refrigerators. Air trapped inside acts as insulator.insulating cavity wall, Used in the buildings to prevent heatdouble- glazed glass from entering by conduction duringAluminum Plastics the day and prevent heat loss at night.
There are many uses of heat flow inour daily life:a. The flow of heat through conduction is used for cooking and boiling. Conduction of heat is also applied in electric irons, ovens and toasters.b. The flow of heat by convection and radiation is used to dry wet clothes, salted fish and others. Drying wet clothes
c. Heat flow through radiation gives us hot water whenwe use a solar heater to absorb heat from the Sun.d. Convection currents can help to improve aircirculation and cool our houses and buildings. Fans andair conditioners help to cool the surrounding airthrough convection currents Air conditioner.
e. Our life can be made healthier and morecomfortable with a good ventilation system in ourhouses. Windows, opening and exhaust fans are thingsthat can help to improve the ventilation of air in ahouse. Warm air inside the house can be drawn outand replaced with fresh, cool air from the outside.