Presentation on theme: "May-14General Science Chapter 141 Heat and Temperature Chapter 14."— Presentation transcript:
May-14General Science Chapter 141 Heat and Temperature Chapter 14
May-14General Science Chapter 142 Temperature What do you know about temperature? Hot and cold can be used to describe temperature. Heat is related to temperature, but they are not the same thing.
May-14General Science Chapter 143 Heat The energy that flows from something with a higher temperature to something with a lower temperature. Always flows from warmer to cooler Heat is measured in joules
May-14General Science Chapter 144 Tiny moving particles All matter is made up of tiny particles that are in constant motion. (Kinetic Theory) The particles have kinetic energy. The faster they move, the more kinetic energy they have. Temperature is a measure of the average kinetic energy of the particles in a sample of matter.
May-14General Science Chapter 145 Temperature Which particles are moving faster, those in a hot cup of coffee or those in a bowl of ice cream? The coffee – higher temperature means more kinetic energy, which means that the particles are moving faster
Temperature We use thermometers to measure changes in temperatures. Absolute Zero: Lowest temperature that an object can have ( °C) Common units for temperature are KelvinSI unit Celsius Fahrenheit May-14General Science Chapter 146
Temperature conversions May-14General Science Chapter 147 K = C C = K - 273
May-14General Science Chapter 148 Heat and Phase Changes Heat is the transfer of energy from a warmer temperature to a cooler temperature. In some cases this temperature change will cause the substance to go through a phase change
May-14General Science Chapter 149 Phase Changes Solid to a liquid ---- Melting Liquid to a gas ---- Evaporation Gas to a liquid ---- Condensation Liquid to a solid ---- Freezing When sufficient heat is added or removed from a substance (which slows or increases the motion of the particles) a phase change will occur
May-14General Science Chapter 1410 Phase Changes The temperature at which the phase occurs is called the melting point or freezing point, etc. Melting point and Freezing point occur at the same temperature It just depends on whether the substance is gaining heat or losing heat Therefore evaporation point/boiling point and condensation point occur at the same temperature
May-14General Science Chapter 1411 Heating curve for water
May-14General Science Chapter 1412 Heating Curve Important information for the heating curve What is the independent variable? What is the dependent variable? Can you identify what phase a substance is in when looking at the heating curve? Can you identify where phase changes occur on the heating curve?
May-14General Science Chapter 1413 Discussion #1 Why do ice cubes melt when you put them in your drink? What is absolute zero and what is the value of absolute zero? What does temperature measure? What are the 3 temperature scales?
May-14General Science Chapter 1414 Discuss #1 What happens to molecules during a phase change? Explain the parts of the heating curve. Explain what is happening on the constant sloped lines on the heating curve. What is a phase change and what are 3 examples?
May-14General Science Chapter 1415 Conduction The transfer of energy by direct contact of particles. When particles collide, the faster moving one gives some of its energy to the slower moving one.
May-14General Science Chapter 1416 Conduction Can transfer energy through a given material or from one material to another. Example: holding a metal spoon with one end in boiling water. Can take place in solids, liquids, or gases. Solids usually conduct heat better particles are closer together
May-14General Science Chapter 1417 Conductors Good heat conductors – materials that transfer heat easily. Metals Poor heat conductors – dont conduct heat easily plastic wood glass fiberglass
May-14General Science Chapter 1418 Reducing heat flow Good heat insulators reduce the flow of heat. They are bad heat conductors Gases such as air Wood Plastic Glass fiberglass
May-14General Science Chapter 1419 Air pockets Many insulating materials make use of small pockets of air inside them. The pockets are too small to allow convection currents to form, so they are good insulators. Styrofoam coolers Down blankets Insulation for your house
May-14General Science Chapter 1420 R-value Resistance to heat flow Higher values mean it is a better insulator. You should use higher R-value materials in roofs and ceilings because more heat escapes upward by convection currents.
May-14General Science Chapter 1421 Double-paned windows Heat is lost through glass windows. By putting a thin layer of air between two panes of glass gives a window a higher R- value. High R-values keep heat inside in the winter and outside in the summer.
May-14General Science Chapter 1422 Thermoses Also called vacuum bottles. Contain a double glass wall with a vacuum in the middle to prevent heat transfer.
May-14General Science Chapter 1423 Fluid Any material that can flow Liquid or gas Air is a common example
May-14General Science Chapter 1424 Convection The transfer of energy by the movement of matter The particles move from one place to another, carrying the energy with them. When a fluid is heated, the particles move faster. Since they can move, they do – and they spread out. Fluids expand when heated.
May-14General Science Chapter 1425 Heating water When the water at the bottom gets hot, it expands, and becomes less dense. The cooler, more dense water above it sinks and pushes the warm water up. As the water rises, it becomes cooler and more dense, and moves towards the bottom again.
May-14General Science Chapter 1426 Convection currents This movement creates convection currents that transfer energy from warmer to cooler parts of the fluid.
May-14General Science Chapter 1427 Radiation The transfer of energy in the form of invisible rays. Does not require matter to be present. Radiant energy – energy that travels by radiation
May-14General Science Chapter 1428 Energy from the sun Radiant energy it travels through mostly empty space to reach us. Shiny materials reflect radiant energy, while dull materials absorb it. Dark-colored materials absorb more radiant energy than light-colored materials.
May-14General Science Chapter 1429 Discussion #2 List the 3 types of heat transfer What is a convection current? What is the difference between an insulator and a conductor? List 3 insulators and 3 conductors. What does an R-value tell us? What is the advantage of a double pane window?
May-14General Science Chapter 1430 Discuss #2 What is conduction? What is radiation? What is convection? Why do birds fluff their feathers and mammals fluff their fur to keep warm?
May-14General Science Chapter 1431 Specific Heat Different materials require different amounts of energy to produce the same temperature change. The specific heat (C p ) of a material is the amount of energy it takes to raise the temperature of 1 kg of the material 1 degree Celsius. Units are J/kg°C Also called heat capacity
May-14General Science Chapter 1432 Specific heat Water has a high specific heat, so it takes a lot of energy to raise its temperature. Thats why the temperature of a lake or unheated swimming pool is always cooler than the temperature of the air around it.
May-14General Science Chapter 1433 Using Specific heat We cant measure change in thermal energy directly. However, we can measure the change in temperature and use the specific heat to calculate the change in thermal energy.
May-14General Science Chapter 1434 Change in Thermal Energy
May-14General Science Chapter 1435 Delta The Greek letter (delta) means change in T means change in temperature Always take final temperature minus initial temperature. When T is positive, the object has increased in temperature and taken in heat. When T is negative, the object has decreased in temperature and given off heat.
May-14General Science Chapter 1436 Example Calculate the thermal energy change when 230 g of water warms from 12 °C to 90 °C. Q = mC p T Q = (0.230 kg)(4184J/kg°C)(90 °C – 12 °C) Q = (0.230 kg)(4184 J/kg°C )(78 °C) Q = J
May-14General Science Chapter 1437 You try A 3.1 kg block of aluminum cools from 35°C to 20 °C. What is the change in its thermal energy? Q = (3.1 kg)(-15 °C)(920 J/kg°C) Q= J
May-14General Science Chapter 1438 Discussion #3 What do each of the symbols in the equation Q = mC p T stand for? What substance has the larger specific heat? Water or Aluminum Would 750 grams of Iron (C p = 500) or 750 grams of Zinc (C p = 800) require more energy to warm up? Explain Would your answer above change if the substances were cooling down? Why?
May-14General Science Chapter 1439 Stoves or fireplaces Simplest heating systems Fuel is burned in the area to be heated Heat transferred to surrounding air by conduction, convection, and radiation.
May-14General Science Chapter 1440 Radiator Device with a large surface area Heats surrounding air by conduction Convection currents carry warm air throughout the room.
May-14General Science Chapter 1441 Radiator (Hot water or Steam) A fuel is burned to heat water. The hot water travels through pipes to the radiator. Or, the water is boiled and the steam travels through the pipes The cooled water or steam returns to the furnace to heat again.
May-14General Science Chapter 1442 Forced air Fuel is burned to heat air. A blower forces the warm air into a room. Convection currents carry the warm air throughout the room. Cool air returns to the furnace to heat again.
May-14General Science Chapter 1443 Radiant Heat (electric or water) Heating coils in the floor or ceiling are heated by electricity or with water. Nearby air is heated by conduction. Materials in the room are heated by radiation.
May-14General Science Chapter 1444 Radiant Energy Examples Pictures from Zach Wiltse
May-14General Science Chapter 1445 Heat Pump Heat energy is collected with a network of coiled pipes on the outside of the home. Heat from the ground evaporates a liquid inside the coils. The vapor moves to a condenser which increases the pressure to increase the temperature of the vapor further.
May-14General Science Chapter 1446 Heat Pump The heated vapor warms the surrounding air. The heated air is moved through the building with a blower, similar to a forced air system. As the vapor cools, it condenses to a liquid and is returned to network of pipes on the outside of the home to repeat the process
May-14General Science Chapter 1449 Solar Heating Uses energy from the sun. Two kinds of solar heating passive active
May-14General Science Chapter 1450 Passive solar heating Windows allow solar energy in. It is absorbed as thermal energy by materials in the room. Later, it is released to the room.
May-14General Science Chapter 1451 Active solar heating Collectors on the roof or the south side of the building. (solar collectors) Energy is absorbed by liquid in pipes in collectors. Heated liquid runs through house to radiators. Cooled liquid returns to collectors
May-14General Science Chapter 1452 Discussion #4 List the 5 main types of central heating systems. What are the 2 types of solar heating? What is the difference between the 2 types of solar heating?
May-14General Science Chapter 1453 Discuss #4 What types of heating systems heat by conduction? What types of heating systems heat by convection? What types of heating systems heat by radiation?
May-14General Science Chapter 1454 Thermal Expansion An increase in volume of a substance due to a change in the substances temperature As materials heat up the particles begin to move faster, this makes them spread apart slightly in all directions. Freezing water, thermostat, an inner tube on a bicycle tire
May-14General Science Chapter 1455 Thermal Expansion Expansion joints Gaps that allow materials to expand and contract with temperature changes Metal joints on bridges Spaces with tar in sidewalks
Thermodynamics 1 st Law of Thermodynamics: The net change in energy equals the energy transferred as work and heat 2 nd Law of Thermodynamics: energy transferred as heat always moves from objects of high temperature to objects of low temperatures. The total disorder of a system will increase. May-14General Science Chapter 1457
Entropy Measure of the amount of disorder in a system. Symbolized by the letter S. Higher temperature = more entropy Lower temperature = less entropy Gas > Liquid > Solid May-14General Science Chapter 1458
May-14General Science Chapter 1459 Heat movers If heat always flows from warmer to colder, how do refrigerators move the warm air from inside to the even warmer air outside? Work must be done This work is powered by electricity.
May-14General Science Chapter 1460 Heat movers Devices that remove thermal energy from one location and transfer it to another location at a different temperature.
May-14General Science Chapter 1461 Cooling systems (Fridge or AC) Main purpose of a cooling system is to remove heat energy by use of refrigerants The refrigerant will gain heat energy from the surrounding environment. The refrigerant begins in the liquid form causing it to evaporate as it gains heat energy. The refrigerant then travels to a compressor to remove the heat and condense back to a liquid and begin the process again.
May-14General Science Chapter 1462 Refrigerants Cooling systems use refrigerants to help remove the heat energy. Chemicals used in cooling systems that usually evaporate quickly at low temperatures. Air, water, ammonia and carbon dioxide are common natural refrigerants Freon is the most commonly used refrigerant, because it is nontoxic, odorless, and non- corrosive. Freon is harmful to the environment
May-14General Science Chapter 1463 Other heat movers Air conditioners – work like refrigerators, only they are designed to cool larger areas. Heat pumps – work like air conditioners when it is warm out. When it is cold, they take thermal energy from the cold air outside and transfer it inside the house.
May-14General Science Chapter 1464 Your bodies cooling system People normally sweat when they become warm. Our body does this so the sweat evaporates by using the heat from our bodies. The heat used from our body to evaporate the sweat makes our bodies feel cooler due to the transfer of heat.
May-14General Science Chapter 1465 Discussion #5 Before there were refrigerators, people had iceboxes. Ice was placed on the top shelf of an insulated box, and food was placed on the shelves below it. How did this work?
May-14General Science Chapter 1466 Discuss #5 What is a heat mover? List some examples of heat movers
May-14General Science Chapter 1467 Heating curve for Iron