Temperature and Heat Heat Temperature Internal Energy Measurement of Heat Specific Heat Thermal Expansion
Temperature & Heat • Absolute Zero Video – Nova • Heat Mixes Lab • Antifreeze in the Summer Lab
Temperature • The quantity that tells how hot or cold something is compared with a standard.
Temperature • Temperature is a measure of the average kinetic energy of the molecules of a substance. • A thermometer measures this KE as the molecules collide with the thermometer’s bulb.
Temperature ScalesFreezing point to boiling point of water • Fahrenheit: 32 to 212, range of 180 degrees. • Celsius: 0 to 100, range of 100 degrees. • Kelvin: 273 to 373, range of 100 degrees.
Kelvin Scale • At constant pressure the volume of a gas changes by 1/273 of its volume at 0Co with each 1Co change in temperature. • At -273 0Co the gas is reduced to 273/273 and the volume is 0.
Heat Some two hundred years ago heat was thought to be an invisible fluid called caloric, which flowed like water from hot objects to cold objects. Caloric appeared to be conserved – that is, it seemed to flow from one place to another without being created or destroyed. This idea was the forerunner of the law of conservation of energy.
Heat is Kinetic Energy • During the French Revolution Count Von Rumford (Benjamin Thompson) was boring cannons for the Bavarian army and he notice: “I perceived, by putting my hand into the water and touching the outside of the cylinder that, Heat was generated; … at 2 hours and 30 minutes it (the water) ACTUALLY BOILED…without any fire.” • The generation of heat was related to the kinetic energy of truing the cannon barrel.
HeatHeat is the net energy transferred from one object to another because of a temperature difference. Internal Energy Includes: • molecular translation form place to place, • molecular vibration, • molecular rotate.
Heat versus temperature Temperature • A measure of hotness or coldness of an object • Based on average molecular kinetic energy Heat • Based on total internal energy of molecules • Doubling amount at same temperature doubles heat
Thermal Equilibrium • When object on contact with each other reach the same temperature and heat no longer flows between them.
How do we measure temperature? Think about using a thermometer
The molecules of the substance bump into the thermometer and transfer energy. How often and how hard they bump into the thermometer are directly related to their speed. Temperature turns out to be related to the average speed of the molecules in a substance.
Temperature is not a measure of the total amount of energy in an object. Thermal Energy = internal energy = a measure of the total kinetic and potential energy in an object
Measurement of Heat • Heat is energy and thus has units of Joules. • However, heat has a special unit of calorie. • A calorie is the heat needed to raise one gram of water by 1Co. • 1cal = 4.186J • 1kcal = 1000 cals • 1Cal (food calorie) = 1000 cals
Specific Heat • Each substance has its own specific heat. • The specific heat of any substance is the amount of heat it takes to raise 1kg of the substance by 1Co. • Specific heat of water = 1.000 kcal/kgCo. • H = mcDT, Where: m = mass c = specific heat DT = change in temperature.
Thermal Expansion • Why? • The Bridge Connection Lab • Concept Development - Thermal Expansion
Thermal Expansion • Bimetallic Strip • Ball and ring • Drinking Bird • Soda Can (Yes, I can make it work!)
Expansion of Water • This is a good thing. • Water temp. vs. depth.
Yeah! Chapter Problems. • Chapter 21: 2, 4, 5, 9, 10, 12, 13, 14, 15, 17, 19, 20, 23, 26, 28, 30, 31, 33 & 34.
Heat Transfer • Conduction • Convection • Radiation • Absorption of Radiant Energy • Emission of Radiant Energy • Newton’s Law of Cooling • Global Warming / Greenhouse Effect
Solar Equality Lab • Purpose: To determine the power output of the sun.
Heat Transfer Three mechanisms for heat transfer due to a temperature difference • Conduction • Convection • Radiation Natural flow is always from higher temperature regions to cooler ones
Conduction • Conduction – • Conductor – • Insulator
Conduction • Heat flowing through matter • Mechanism • Hotter atoms collide with cooler ones, transferring some of their energy • Direct physical contact required; cannot occur in a vacuum • Poor conductors = insulators (Styrofoam, wool, air…)
Convection • Convection -
Convection • Energy transfer through the bulk motion of hot material • Examples • Space heater • Gas furnace (forced) • Natural convection mechanism - “hot air rises”
Heat TransferThe Wind Sea Breeze Land Breeze
Convection • Why does rising warm air cool?
Radiation • Radiation
Radiation • Radiant energy - energy associated with electromagnetic waves • Can operate through a vacuum • All objects emit and absorb radiation • Temperature determines • Emission rate • Intensity of emitted light • Type of radiation given off • Temperature determined by balance between rates of emission and absorption • Example: Global warming
Radiation • Absorption of Radiant Energy – • Emission of Radiant Energy – • Con. Dev. 22-1 Transmission of Heat
Global Warming • What causes it?
Video • An Inconvenient Truth
Yeah! More Problems • Chapter 22: 1, 2, 3, 4, 7, 8, 9, 12, 16, 17, 19, 20, 21, 22, 24, 25, 26, 27 & 28.
Chapter 24 Thermodynamics: Laws of Thermodynamics Song: http://www.youtube.com/watch?v=KTHiIwxcexI
The study of heat and its relationship to mechanical and other forms of energy Thermodynamic analysis includes System Surroundings (everything else) Internal energy (the total internal potential and kinetic energy of the object in question) Energy conversion Friction - converts mechanical energy into heat Heat engines - devices converting heat into mechanical energy Other applications: heat pumps, refrigerators, organisms, hurricanes, stars, black holes, …, virtually any system with energy inputs and outputs Thermodynamics
Absolute Zero • Define: • Compared to Celsius:
Lab • The Uncommon Cold - #63