1 Temperature Temperature is a measure of how hot or cold an object is compared to another object. indicates that heat flows from the object with a higher temperature to the object with a lower temperature. is measured using a thermometer. Average Kinetic Energy of the atoms Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

2 Temperature Scales Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings are Fahrenheit, Celsius, and Kelvin. have reference points for the boiling and freezing points of water.

3 A. What is the temperature of freezing water? 1) 0°F 2) 0°C 3) 0 K B. What is the temperature of boiling water? 1) 100°F 2) 32°F 3) 373 K C. How many Celsius units are between the boiling and freezing points of water? 1) 1002) 1803) 273 Learning Check

4 A. What is the temperature of freezing water? 2) 0°C B. What is the temperature of boiling water? 3) 373 K C. How many Celsius units are between the boiling and freezing points of water? 1) 100 Solution

5 On the Fahrenheit scale, there are 180°F between the freezing and boiling points and on the Celsius scale, there are 100°C. 180°F = 9°F =1.8°F 100°C 5°C 1°C In the formula for the Fahrenheit temperature, adding 32 adjusts the zero point of water from 0°C to 32°F. T F = 9/5 T C + 32  or T F = 1.8 T C + 32  Fahrenheit Formula

6 T C is obtained by rearranging the equation for T F. T F = 1.8T C + 32 Subtract 32 from both sides. T F - 32 = 1.8T C ( ) T F - 32 = 1.8T C Divide by 1.8 =°F - 32 = 1.8 T C T F - 32 = T C 1.8 Celsius Formula

7 Solving A Temperature Problem A person with hypothermia has a body temperature of 34.8°C. What is that temperature in °F? T F = 1.8 T C + 32  T F = 1.8 (34.8°C) + 32° exact tenth's exact = ° = 94.6°F tenth’s Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

8 The normal temperature of a chickadee is 105.8°F. What is that temperature on the Celsius scale? 1) 73.8°C 2) 58.8°C 3) 41.0°C Learning Check

9 3) 41.0 °C T C = (T F - 32°) 1.8 =( °) 1.8 =73.8°F = 41.0°C 1.8° Solution

10 A pepperoni pizza is baked at 455°F. What temperature is needed on the Celsius scale? 1) 423°C 2) 235°C 3) 221°C Learning Check

11 A pepperoni pizza is baked at 455°F. What temperature is needed on the Celsius scale? 2) 235°C T F - 32° = T C 1.8 ( °) = 235°C 1.8 Solution

12 On a cold winter day, the temperature is –15°C. What is that temperature in °F? 1) 19°F 2) 59°F 3) 5°F Learning Check

13 3) 5°F T F = 1.8 T C + 32  T F = 1.8(–15°C) + 32° = – ° = 5°F Note: Be sure to use the change sign key on your calculator to enter the minus – sign. 1.8 x 15 +/ – = –27 Solution

14 The Kelvin temperature scale has 100 units between the freezing and boiling points of water. 100 K = 100°Cor 1 K = 1°C is obtained by adding 273 to the Celsius temperature. T K = T C contains the lowest possible temperature, absolute zero (0 K). 0 K = –273°C Kelvin Temperature Scale

15 Temperatures TABLE 2.5

16 What is normal body temperature of 37°C in Kelvins? 1) 236 K 2) 310. K 3)342 K Learning Check

17 What is normal body temperature of 37°C in kelvins? 2) 310. K T K = T C = 37°C = 310. K Solution

HEAT ENERGY What is HEAT? Form of energy and measured in JOULES Particles move about more and take up more room if heated – this is why things expand if heated It is also why substances change from: solids liquids gases when heated Visit for more free powerpointswww.worldofteaching.com

Heat and Temperature The temperature of an object tells us how HOT it is Measured in degrees Celsius - °C It is NOT the same as heat energy although the two quantities are related. e.g. a beaker of water at 60 °C is hotter than a bath of water at 40 °C BUT the bath contains more joules of heat energy

Heating and Cooling If an object has become hotter, it means that it has gained heat energy. If an object cools down, it means it has lost energy

Heating and Cooling cont… Heat energy always moves from: HOT object COOLER object e.g.Cup of water at 20 °C in a room at 30°C - gains heat energy and heats up – its temperature rises Cup of water at 20 °C in a room at 10°C loses heat energy and cools down – its temperature will fall.

Specific Heat Capacity Or the amount of energy needed to heat substances up

Specific Heat Capacity can be thought of as a measure of how much heat energy is needed to warm the substance up. You will possibly have noticed that it is easier to warm up a saucepan full of oil than it is to warm up one full of water. manufacturer.com/photo/418fa6490f24202f2cc5b5feee0fdde3/Aluminu m-Saucepan.jpg

Specific Heat Capacity (C) of a substance is the amount of heat required to raise the temperature of 1g of the substance by 1 o C (or by 1 K). The units of specific heat capacity are J o C -1 g -1 or J K -1 g -1. Sometimes the mass is expressed in kg so the units could also be J o C -1 g -1 or J K -1 kg -1

Approximate values in J / kg °K of the Specific Heat Capacities of some substances are: Air 1000Lead 125 Aluminium900 Mercury 14 Asbestos840 Nylon 1700 Brass 400 Paraffin 2100 Brick 750 Platinum 135 Concrete3300 Polythene 2200 Cork 2000 Polystyrene 1300 Glass 600 Rubber 1600 Gold 130 Silver 235 Ice 2100 Steel 450 Iron 500 Water 4200

HEAT ENERGY Energy transfer Conduction Convection Radiation

Conduction Heat is transferred through a material by being passed from one particle to the next Particles at the warm end move faster and this then causes the next particles to move faster and so on. In this way heat in an object travels from: the HOT end the cold end

Conduction cont… Occurs by the particles hitting each other and so energy is transferred. Can happen in solids, liquids and gases, Happens best in solids-particles very close together Conduction does not occur very quickly in liquids or gases

Conductors Materials that conduct heat quickly are called conductors All metals are good conductors of heat Copper is a very good conductor of heat Pans for cooking are usually made with a copper or aluminium bottom and plastic handles

Insulators/poor conductors Materials that conduct heat slowly or poorly are called insulators Glass, wood, plastic and rubber are poor conductors (good insulators) Nearly all liquids including water are poor conductors (good insulators) Gases, including air are poor conductors,e.g., wool feels warm because it traps a lot of air A fridge has insulation material round it to keep it cold – reduces amount of heat conducted to inside from the warmer room

Convection Takes place in material where particles can move around inside the material, i.e. liquid or gas The heat is carried by the particles themselves moving Convection currents Occur because an area with warm particles expands and becomes less dense than the cooler areas nearby. The warm area rises. Cooler particles fall into the space left by the warm particles and convection current is set up

Convection Currents Hot liquids and gases expand and rise while the cooler liquid or gas falls 1. Hot air rises 2. Goes across 3. Then down 4. And across

Convection cont… The sun can cause large convection currents - WINDS During daytime the land warms up more than the sea. The warm air rises over the land and cool air falls over the sea. So we feel a sea breeze. Rising convection currents can be uses by glider pilots to keep their planes in the air and by birds to stay aloft.

Radiation Transfer of heat directly form the source to the object by a wave, travelling as rays. Heat radiation is also known as All objects that are hotter than their surroundings give out heat as infra-red radiation Heat transfer by radiation does not need particles to occur and is the only way energy can be transferred across empty space INFRA-RED RADIATION

Emitters Hotter objects emit (give out) heat Different surfaces emit heat at different speeds A dull black surfaces loses energy more quickly – it is a good radiator A bright shiny or white surface is a poor radiator Marathon runners need to keep warm at the end of races, covering in shiny blankets reduces radiation and therefore heat loss.

Emitters of heat Bright shiny can Poor radiator Dull black can Good Radiator

Absorbers Cooler objects absorb (take in) heat Substances absorb heat at different speeds Dull, black surfaces absorb heat quickly Bright, shiny surfaces absorb heat slowly In hot countries, people wear bright white clothes and paint their houses white to reduce absorption of energy from the sun. Petrol storage tanks sprayed silver to reflect sun’s rays

Absorbers Shiny, bright can Poor absorber Dull black can Good absorber

Key Words Heat Radiation Convection Conduction Cold Insulator Conductor Temperature Emitter Absorber Transfer