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# 2º ESO UNITt 1 HEAT. NOTES

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### 2º ESO UNITt 1 HEAT. NOTES

1. 1. Unit 1 Heat Science 2º ESO 1 UNIT 1: HEAT (MATTER ENERGY AND HEAT) 1. Matter and magnitude 2. Energy 3. Law of conservation of energy 4. Thermal energy, Temperature and Heat 5. Thermometer and Temperature Scales 6. Important items about Temperature and Heat 7. Transmission of heat 8. Effect of heat 1. Matter, magnitude Definition: is anything that has mass and occupies volume. Magnitud, magnitude: They are those properties of matter that we can measure. For example: length, mass, temperature…, are magnitudes, but colour, beauty are not magnitudes. To measure magnitudes we need a number followed by its unit, length: metre (m), mass: gram (g). 2. Energy. Definition: It´s the magnitude that measures the ability of a system to do work, that means, produces changes or effect. Examples:  Water erodes the hillside;  Sun heats the water in oceans and evaporates it, For example: Glass on the table: 1. How has put the glass on the table? Somebody (has produce a changes = energy) 2. Why has the glass fallen down? Because of a earthquake (has produce a changes = energy) 3. Why is the glass going through the floor? Because of gravity law
2. 2. Unit 1 Heat Science 2º ESO 2 4. Why is it broken? Because the floor stops the glass and pushes it up All of them are changes, transformations, so they are energies In the international system, the unit that measures energy is the joule (J) in honor of Jean Prescott Joule. 3. Law of conservation of energy, Mayer (1845) "Energy can be neither created nor destroyed, but it can be transferred or transformed from one form to another” Law of conservation of mass, Lavoisier “mass can be neither created or destroyed, just can be transformed” Types of energies We must difference several types or energy:  Kinetic energy related to movement  Potential energy related to the position that a body has  Mechanic energy related to movement and position that a body has  Thermal energy related to heat  Chemical energy related to composition that a body has  Nuclear energy related to atoms  Electrical energy related to electric charge  Electromagnetic energy related do electromagnetic waves 4. Thermal energy, Temperature and Heat There are three concepts that we usually confuse: thermal energy, temperature and heat 4.1. Thermal Energy: Remember:
3. 3. Unit 1 Heat Science 2º ESO 3 As a consequence of movement, each atom has kinetic energy, if we calculate average kinetic energy of atoms which composes a body, we’ll have the thermal energy that the body has Definition: Thermal energy is the average kinetic energy of the particles that a body has 4.2. Temperature: Temperature is the magnitude that measures thermal energy 4.3. Heat Heat is thermal energy which transfers (flows) from one body to another, heat is transference of energy Heat flows in one direction, from the higher temperature body to the lower temperature body Heat flow stops when the temperatures are the same; this is called thermal equilibrium. For example, if you place an iron bar, heated to 80 °C, into a container of water at 15 °C, the iron bar will lose heat and the water will absorb it. This thermal transfer of energy will stop when the iron bar and the water are at the same temperature. Unit of measurement of heat is the Joule (J) SI; calorie is another unit of measurement. One joule is equal to 0,24 calories 1 cal = 4,18 J 1 J = 0,24 cal When do heat flow stop? Heat flow (transfer) stops when the bodies in contact, rise the same temperature In winter, your body is warmer than the environment, As a result, you lose heat. Clothes trap the warm air and prevent heat loss
4. 4. Unit 1. Heat Notes Science . 2º ESO 4 5. Thermometer and temperature scales Thermometer is the instrument that we use to measure temperature. Thermometer uses liquids which expand when heat up and contract when cool down How is temperature measured? Temperature is measured on three scales: Celsius, Fahrenheit and Kelvin  The Celsius scale (ºC), also called Centigrade, is the most used in our country. The freezing point of water is 0ºC and the boiling point is 100ºC  Fahrenheit scale: is used in some English-speaking countries. The freezing point of water is 32ºF and the boiling point is 212ºF To convert Celsius to Fahrenheit or vice versa: ºF = ºC · 1,8 + 32 ºC = (ºF – 32)/1,8  Kelvin scale or absolute scale (K) is used by scientists. The big difference is that it is based on a single point: 0 degrees Kelvin (absolute zero): when atoms don’t move, or they have minimum speed, they have 0 Kelvin Kelvin is the unit in the International System. To convert Celsius to Kelvin vice versa: C = K - 273 k = C + 273 6. Important items about heat and temperature Did you know that... Anders Celsius (1701-1744), was a Swedish astronomer. He was the first to propose the Centigrade scale.
5. 5. Unit 1. Heat Notes Science . 2º ESO 5 7. Transmission of heat Heat transfers by conduction, convection and radiation. Conduction and convection need matter to transfer heat, but radiation can be transmitted through space. a. Conduction occurs in most solids. Heat is transferred by direct contact. When two substances at different temperatures are in contact, heat flows from the warmer substance to the cooler one. The heat flow stops when the substances reach the same temperature, that is, thermal equilibrium. Good conductors of heat, like metal, transmit thermal energy quickly. Good insulators of heat, like plastic and wood, transmit thermal energy slowly. b. Convection only occurs in liquids and gases (fluid). Heat is transferred by the movement of currents. Warm liquids and gases rise because they are lighter than cold liquids and gases. Cold liquids and gases fall because they are heavier than warm liquids and gases. So currents move around in a circle. Central heating uses convection to heat a room. The warm air rises, and the cooler air falls to be heated again. c. Radiation is the transfer of heat by several types of waves (electromagnetic…). No contact is necessary between the source and the heated substance. It is the fastest form of heat transfer. Radiation can even transmit heat through the vacuum of space. We feel the heat of the Sun, although it's 150,000,000 km away. Conductors are substances which allow heat to move through them easily. They conduct heat efficiently. Metals are good Conductors, Heat from the Sun can be felt, but cannot be touched. Heat transfers through the space between the Sun and the Earth. Insulators are substances which do not allow heat to move through themeasily! Cork, air and plastics are Insulators,
6. 6. Unit 1. Heat Notes Science . 2º ESO 6 8. Effect of Heat  Cambio de temperatura: cuando un cuerpo cede o gana calor, su temperatura cambia. Ese cambio de temperatura depende de las sustancias que componga el material y de la masa. Por ej para calentar 1 kg de hierro necesitamos 473J, sin embargo para calentar 1kg de agua necesitamos 4.183 J. llamamos calor específico de una sustancia a la cantidad de calor que hay que aplicar a 1 kg de cualquier sustancia para aumentar su temperatura en 1 grado. Además la cantidad de masa que queramos calentar también influye: para calentar 5kg de hierro tendremos que aplicarle 5 x 473 J  Cambio de volumen: otro efecto del Q es el cambio de volumen de los cuerpos: dilatación, el volumen aumenta cuando el cuerpo gana calor, o contracción, el volumen disminuye cuando el cuerpo cede calor  Cambio de estado: ya sabemos que el calor genera cambios de estado (sol, líq y gaseoso). Analicemos como científicos como ocurren estos cambios de estado con la siguiente gráfica: