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General Science Chapter 14

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Presentation on theme: "General Science Chapter 14"— Presentation transcript:

1 General Science Chapter 14
Heat and Temperature Chapter 14 Mar-17 General Science Chapter 14

2 General Science Chapter 14
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. Mar-17 General Science Chapter 14

3 General Science Chapter 14
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 Mar-17 General Science Chapter 14

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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. Mar-17 General Science Chapter 14

5 General Science Chapter 14
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 Mar-17 General Science Chapter 14

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Temperature We use thermometers to measure changes in temperatures. Absolute Zero: Lowest temperature that an object can have ( °C) Common units for temperature are Kelvin SI unit Celsius Fahrenheit Mar-17 General Science Chapter 14

7 Temperature conversions
K = C + 273 C = K - 273 Mar-17 General Science Chapter 14

8 General Science Chapter 14
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 Mar-17 General Science Chapter 14

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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 Mar-17 General Science Chapter 14

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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 Mar-17 General Science Chapter 14

11 Heating curve for water
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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? Mar-17 General Science Chapter 14

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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? Mar-17 General Science Chapter 14

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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? Mar-17 General Science Chapter 14

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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. Mar-17 General Science Chapter 14

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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 Mar-17 General Science Chapter 14

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Conductors Good heat conductors – materials that transfer heat easily. Metals Poor heat conductors – don’t conduct heat easily plastic wood glass fiberglass Mar-17 General Science Chapter 14

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Reducing heat flow Good heat insulators reduce the flow of heat. They are bad heat conductors Gases such as air Wood Plastic Glass fiberglass Mar-17 General Science Chapter 14

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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 Mar-17 General Science Chapter 14

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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. Mar-17 General Science Chapter 14

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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. Mar-17 General Science Chapter 14

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Thermoses Also called vacuum bottles. Contain a double glass wall with a vacuum in the middle to prevent heat transfer. Mar-17 General Science Chapter 14

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Fluid Any material that can flow Liquid or gas Air is a common example Mar-17 General Science Chapter 14

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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. Mar-17 General Science Chapter 14

25 General Science Chapter 14
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. Mar-17 General Science Chapter 14

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Convection currents This movement creates convection currents that transfer energy from warmer to cooler parts of the fluid. Mar-17 General Science Chapter 14

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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 Mar-17 General Science Chapter 14

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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. Mar-17 General Science Chapter 14

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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? Mar-17 General Science Chapter 14

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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? Mar-17 General Science Chapter 14

31 General Science Chapter 14
Specific Heat Different materials require different amounts of energy to produce the same temperature change. The specific heat (Cp) 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 Mar-17 General Science Chapter 14

32 General Science Chapter 14
Specific heat Water has a high specific heat, so it takes a lot of energy to raise its temperature. That’s why the temperature of a lake or unheated swimming pool is always cooler than the temperature of the air around it. Mar-17 General Science Chapter 14

33 General Science Chapter 14
Using Specific heat We can’t 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. Mar-17 General Science Chapter 14

34 Change in Thermal Energy
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35 General Science Chapter 14
Delta The Greek letter D (delta) means “change in” DT means change in temperature Always take final temperature minus initial temperature. When DT is positive, the object has increased in temperature and taken in heat. When DT is negative, the object has decreased in temperature and given off heat. Mar-17 General Science Chapter 14

36 General Science Chapter 14
Example Calculate the thermal energy change when 230 g of water warms from 12 °C to 90 °C. Q = m∙Cp∙DT Q = (0.230 kg)(4184J/kg∙°C)(90 °C – 12 °C) Q = (0.230 kg)(4184 J/kg∙°C )(78 °C) Q = J Mar-17 General Science Chapter 14

37 General Science Chapter 14
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 Mar-17 General Science Chapter 14

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Discussion #3 What do each of the symbols in the equation Q = m∙Cp∙DT stand for? What substance has the larger specific heat? Water or Aluminum Would 750 grams of Iron (Cp = 500) or 750 grams of Zinc (Cp = 800) require more energy to warm up? Explain Would your answer above change if the substances were cooling down? Why? Mar-17 General Science Chapter 14

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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. Mar-17 General Science Chapter 14

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Radiator Device with a large surface area Heats surrounding air by conduction Convection currents carry warm air throughout the room. Mar-17 General Science Chapter 14

41 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. Mar-17 General Science Chapter 14

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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. Mar-17 General Science Chapter 14

43 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. Mar-17 General Science Chapter 14

44 Radiant Energy Examples
Pictures from Zach Wiltse Mar-17 General Science Chapter 14

45 General Science Chapter 14
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. Mar-17 General Science Chapter 14

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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 Mar-17 General Science Chapter 14

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Geothermal picture Mar-17 General Science Chapter 14

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Heat Pump Mar-17 General Science Chapter 14

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Solar Heating Uses energy from the sun. Two kinds of solar heating passive active Mar-17 General Science Chapter 14

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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. Mar-17 General Science Chapter 14

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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 Mar-17 General Science Chapter 14

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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? Mar-17 General Science Chapter 14

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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? Mar-17 General Science Chapter 14

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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 Mar-17 General Science Chapter 14

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Thermal Expansion Expansion joints Gaps that allow materials to expand and contract with temperature changes Metal joints on bridges Spaces with “tar” in sidewalks Mar-17 General Science Chapter 14

56 Thermal Expansion Examples
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Thermodynamics 1st Law of Thermodynamics: The net change in energy equals the energy transferred as work and heat 2nd 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. Mar-17 General Science Chapter 14

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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 Mar-17 General Science Chapter 14

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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. Mar-17 General Science Chapter 14

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Heat movers Devices that remove thermal energy from one location and transfer it to another location at a different temperature. Mar-17 General Science Chapter 14

61 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. Mar-17 General Science Chapter 14

62 General Science Chapter 14
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 Mar-17 General Science Chapter 14

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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. Mar-17 General Science Chapter 14

64 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. Mar-17 General Science Chapter 14

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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? Mar-17 General Science Chapter 14

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Discuss #5 What is a heat mover? List some examples of heat movers Mar-17 General Science Chapter 14

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Heating curve for Iron Mar-17 General Science Chapter 14


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