2. HEAT

3. FOODS GIVE US ENERGY TO DO WORK AND PLAY. SEVERAL MILLIONS OF ARGANISMS SUCH AS PLANTS,TREES,ANIMAL AND HUMAN BEINGS LIVE ON THE EARTH. ALL OF THEM ENERGY FROM THE SUN AS HEAT AND LIGHT. THE ENERGY REQUIRED FOR OPERATING MACHINES IS OBTAINED BY BURNING FUELS. LET US LEARN ABOUT HEAT ENERGY IN THIS UNIT. HEAT IS A FORM OF ENERGY. WHEN YOU RUB YOUR HANDS TO GETHER HEAT IS PRODUCED. WHEN A KNIFE,TAMARIND SEED OR ANY OTHER OBJECTS IS RUBBED ON THE FLOOR, IT GETS HEATDED UP. AS LONG AS WE RUB THE OBJECTS HEAT IS CONTINOUSLY PRODUCED BECAUSE OF FRICTION. THE WORK DONE WHILE RUBBING GETS CONVERTED IN TO HEAT ENERGY. WE GET THE HEAT ENERGY REQUIRED FOR COOKING FOOD FROM FIRE-WOOD,COAL,KEROSINE,COOKING GAS AND ELECTRICITY. THEY ARE CALLED SOURCES OF HEAT. THE MAIN SOURCES OF HEAT IS THE SUN WHICH IS BURNING CONTINUOUSLY.

4. AN OBJECT CHANGES ITS SHAPE,PHYSICAL STATE AND TEMPERATURE WHEN IT IS HEATED. TAKE WATER IN A ROUND BOTTOMED FLASK AND PUT A LITTLE SAW DUST INTO IT. HEAT THE FLASK WITH A BURNUR. OBSERVE WHAT HAPPENS. HOW DOES THE SPEED OF THE SAW DUST CHANGE WITH TEMPERATURES? HOW DO THEY GET ENERGY? WHEN THE TEMPERATURES OF WATER INCREASES THE SPEED OF WATER MOLECULES INCREASES. THE SAW DUCT MOVES BECAUSE IT GETS HIT BY MOVING WATER MOLECULES WHEN AN OBJECT IS HEATED THE SPEED OF THE MOLECULES IN IT INCREASES. AS A RESELT THE MOLECULES MOVE APART AND THE OBJECT GETS EXPANDED. THE LENGTH, AREA AND VOLUME OF SOLID OBJECTS INCREASES ON HEATING.

6. DOCTER AND SCIENTITS USE MERCURY THERMOMETERS WHICH WORK ON THE PRIINCIPLE OF THERMAL EXPANSION OF LIQUIDS. THE THERMOMETER IS PLACED IN A BEAKER CONTAINING PURE ICE SHAVINGS. WHEN THE LEVEL OF MERCRY ISV STEADY IT IS MARKED AS O. THIS TEMPERATURE OF MELTING ICE IS CALLED THE LOWER FIXED POINT. THE THEMPERATURE IS KEPT AT THE THEMPERATERATURE OF STEAM AND THE LEVEL OF MERCURY IN THE STEAM IS MARKED AS 100 C. THE TEMPERATURE OF BOILING WATER IS CALLED THE UPPER FIXED POINT OF THE THERMOMETER. THE INTERVAL BETWEEN THE TWO FIXED POINTS IS DIVIED INTO 100 EQUAL. THIS TEMPERATURE SCAL WAS INVENTED BY CELSIUS AND TEMPERATURE IS MDEASURED IN DEGREES CELSIUE. THE TEMPERATURE OF OUR BODY IS36.9C.