Physics chapter 12

Chapter 12

Thermal Energy

Thermal Energy

• The thermal energy of an object is the sum of K.E. and P.E. of the internal motion of the particles that make up an object; it is dependent on mass

• The temperature of an object is the measure of how hot something is on a defined scale; this is the kinetic energy per molecule of an object; not dependent on mass

Thermal Energy

• When a cold object meets a hot object, the cold molecules speed up and the hot molecules slow down until they reach thermal equilibrium. (Zero’th Law of Thermodynamics)

Temperature Conversions

• F = 1.8C + 32

• C = 5/9 (F-32)

• K = C + 273.15

• Farenheit Celcius Kelvin

Physical States of Matter

6 States of Matter0. Einstein-Bose – no motion (no heat)1. Solid – definite shape and volume2. Liquid – definite volume and indefinite shape3. Gas – indefinite shape and volume4. Plasma – gaseous mixture of positively and

negatively charged particles5. Filament – non thermal motion in only one

direction

Heat

• The energy that flows as a result of a temperature difference: heat always flows from warmer regions to cooler regions.

• Specific Heat – amount of energy needed to raise or lower the temperature of a 1kg mass 1 degree Celsius

• Q = mC∆T

Heat –

Filter paper with and with out water

3 Types of Heat Transfer

• Conduction (requires contact) – transfer of K.E. when particles of an object collide

• Convection (requires mass flow) – transfer of heat through movement of fluids with different densities at different temperatures.

• Radiation (fastest) – transfer of heat through space by electromagnetic waves

3 Types of Heat Transfer

•

Heat of Fusion

• The amount of energy needed to melt or freeze 1kg of a substance. (The phase changes, but the temperature does not)

• Q = mHf

Heat of Vaporization

• The amount of energy needed to vaporize or condense 1 kg of a substance (The phase changes but the temperature does not)

• Q = mHv

Heating and Cooling

• Vaporization – cooling process because the faster moving molecules are escaping and leaving the cooler, slower molecules behind.

• Condensation – warming process because as the molecules condense more collisions occur, causing the object to gain heat.

Thermal ExpansionThermal Expansion

• In general, most things will expand when heated and contract when cooled.

• Linear Expansion

• L = Li + ∆L

• ∆L = αLi∆T

• Volume Expansion

• V = Vi + ∆V

• ∆V = βVi∆T

Natural ResourcesNatural Resources

►Sunlight (Solar-power) <1%Sunlight (Solar-power) <1%►Wind (Wind-power) 1%Wind (Wind-power) 1%►Rain (Hydro-power) 6%Rain (Hydro-power) 6%►Tides (Tidal-power, ocean currents) <1%Tides (Tidal-power, ocean currents) <1%►Wave (Wave-power, surface waves) <1% Wave (Wave-power, surface waves) <1% ►Geothermal Heat (Geothermal-Geothermal Heat (Geothermal-

power)<1%power)<1%

Solar & Wind & Tidal Solar & Wind & Tidal & Wave Power& Wave Power

Other Natural ResourcesOther Natural Resources

►Fossil fuels / Biomass Fossil fuels / Biomass (Non-renewable - Coal & Petroleum 86%)(Non-renewable - Coal & Petroleum 86%) (Non-renewable - Nuclear 6%) (Non-renewable - Nuclear 6%) (Somewhat renewable - Wood)(Somewhat renewable - Wood)

►Bio-fuel (Renewable plants used as Bio-fuel (Renewable plants used as fuel) fuel) Ex. E-10 gasolineEx. E-10 gasoline

Non-renewable energy Non-renewable energy sourcessources

►Natural gas (Methane) – CHNatural gas (Methane) – CH44

►Propane – CPropane – C33HH88

►CoalCoal►Oil, petroleumOil, petroleum►Uranium – NuclearUranium – Nuclear

Solar & Wind & Tidal & Wave Power

Advantages – Wide availability Very low emissions

Disadvantages – Tidal and Wave - Cost of harnessing &

building system (1st slated for 2012?) Solar & Wind not continuous (Cost of storing)

Hydro Power

Advantages – Low emissions

Disadvantages – Limited availability Ecological effect on rivers and streams

Natural Gas & Propane & Coal & Petroleum & Nuclear

Advantages Readily available Relatively low cost

Disadvantages Coal & Petroleum & Natural gas &

propane (Emissions) Nuclear (Storage or disposal of nuclear waste)

Wood & Plant Fuels

Advantages Somewhat easy to replenish

Disadvantages Ethanol (plant) fuels have to be replenished

adequately, otherwise this drives up cost of foods Wood has to be re-grown and harvested wisely,

otherwise this drives up costs of wood