Chapter 16 Thermal Energy and Heat Physical Science

Thermal Energy and Matter 16.1 In 1700s, scientist thought heat was fluid called caloric Not fluid or state of matter but related to motion Work and Heat Heat – transfer of thermal E from one object to another bc of temp difference Flow from hot to cold Can occur bc of friction from work Temperature Measure of how hot or cold bc of movement of particle average kinetic E of the particles in an object due to random motion all particle collisions transfer thermal E

The particles inside an ice cube are moving very slowly. The particles in boiling water are moving very fast.

Thermal Energy 16.1 Total potential and kinetic E of all the particles Depends on: Mass Cup of hot tea vs. teaspoon of hot tea Same temp = so same average kinetic energy Cup tea more thermal E b/c more particles Temperature Cup of hot tea vs. cup of cold tea Same mass, same # of particles Different average kinetic E = energy of particle higher in hot tea = greater thermal E Phase (solid, liquid, gas) Phase changes transfer thermal energy

Thermal Contraction and Expansion 16.1 Thermal Expansion – increase in volume of material bc of temp increase  particles move faster  collide more often  expand Gases expand more than liquids, liquids more than solids bc force of attraction is less Thermal Contraction Temperature decreases  particles move more slowly  collide less often

Specific Heat 16.1 Amount of heat needed to raise the temperature of 1 gram of a material by 1 degree Lower specific heat = heat faster Joules per gram per degree Celsius Q = m(c)(ΔT)

Measuring Heat Change 16.1 Calorimeter – instrument used to measure changes in thermal E Used to measure specific heat of Al 

Math Practice # 1- 5 Page 477

Heat and Thermodynamics 16.2 Conduction – transfer of thermal E Not transfer of matter Materials are TOUCHING Slower in gases than liquids, liquids slower than solids bc of particle location Faster in metals bc electrons free to move (sea of e-) Thermal Conductors – material that conducts well Metal Does not have to be hot  tile floor colder than wooden floor bc tile is a better conductor and transfers thermal E quickly to skin Thermal Insulator – material that conducts poorly Wood, air, plastic, foam

Convection 16.2 Transfer of thermal energy when particles of a fluid (liquid or gas) move from place to place Hot to cold Convection current- fluid circulate in a loop as it alternately heats up and cools down Occurs in oceans, weather, and movement of hot rock in Earth’s interior Ovens

Radiation 16.2 Transfer of E by waves moving thru space All objects radiate energy As temp increases, radiation increases

Thermodynamics 16.2 The study of conversions between thermal energy and other forms of energy 1st Law – energy is neither created or destroyed 2nd Law – thermal E can flow from colder to hotter objects only when work is done Relates to entropy (disorganization of system) Heat engines –converts heat into work Efficiency is always less than 100% Waste heat = thermal E not converted to work Spontaneous changes – makes system less orderly unless work is done World is always becoming less orderly 3rd Law – absolute zero (O K) cannot be reached

Solar Homes http://www.youtube.com/my_playlists?pi=0&ps=20&sf=&sa=0&sq=&dm=0&p=CB817BBF0B24D9CA 3 clips = 4 minutes

Heat Engines 16.3 External Combustion Engine – an engine that burns fuel outside the engine 1st used to pump water out of coal mines Hot steam enters in right  valve slide to left  steam trapped  expands and pushes piston  heat converted to work

An External Combustion Engine Figure 11 An External Combustion Engine

An External Combustion Engine Figure 11 An External Combustion Engine

An External Combustion Engine Figure 11 An External Combustion Engine

Heat Engines 16.3 Internal Combustion Engines – Fuel burns inside the engine Most use pistons that move in a cylinder Each motion up and down = stroke Linear motion is converted to rotary motion by crankshaft Crankshaft = connected to transmission (linked to wheels and driveshaft http://www.youtube.com/my_playlists 6 min

An Internal Combustion Engine Figure 12 An Internal Combustion Engine

Heating System 16.3 Central heating system – heats many rooms from 1 central location Commonly used electrical energy, natural gas, oil, and coal Differ in how they transfer thermal energy Hot-Water Heat Circulating pump carries hot water to radiators in each room  conduction (water to radiator)  conduction and radiation (heating room) convection in room Steam Heating Similar to hot water heat but use steam instead Often used in older buildings Electric Baseboard Heating Use electric energy (convert electrical to thermal) Hot coils heat air by conduction and radiations  convection causes circulation Space heaters are similar Forced-Air Heating Use fans to circulate air thru ducts to rooms  convection circulates air in room b/c warm air rises, warm-air vents are located in floor Advantage = air is cleaned as pass thru filters

Cooling Systems 16.3 Heat pump – device that reverses the normal flow of thermal heat Refrigerant – fluid that vaporizes and condenses inside the tubing of a heat pump Absorbs heat  vaporizes  turns into gas Gives off heat  condenses  turns into liquid Heat pump must do work to refrigerant to reverse flow Refrigerators- heap pump that transfers thermal E from cold food compartment to warm room Open door adds more heat to room than it removes b/c coils get hotter Air Conditioner Must do work

http://www.expertvillage.com/video/165820_do-refrigerators-work.htm 2 minutes