Physical Science Heat and Thermodynamics Chapter 16 Section Two

Science Journal Entry 30 Explain the differences and similarities, between conduction, convection and radiation.

Conduction  Conduction is the transfer of heat energy by direct contact. No matter is transferred only energy.  Conduction in gases is slower than in liquids and solids because the particles in a gas collide less often since they are farther apart.  Conduction is faster in metals, not only because they are solid but because some electrons in them are free to move about.  A thermal conductor is a material that conducts thermal energy well. A thermal insulator is a material that conducts thermal energy poorly.

Convection  Convection is the transfer of thermal (heat) energy when particles of a fluid move from one place to another.  A Convection Current circulates within a fluid as the fluid alternately heats up and cools down. The warm fluid (even air) rises but the colder fluid sinks creating a loop-like cycle. Convection currents occur in many important natural cycles, such as ocean currents, weather systems, and movements of hot asthenosphere in Earth’s Interior.

Radiation  Radiation is the t ransfer of heat energy by electromagnetic waves such as the solar radiation of the sun or a radiator providing heat for an apartment.  All objects radiate energy. As an object’s temperature increases, the rate at which it radiates energy increases.  5:05

First Law of Thermodynamics  Thermodynamics is the study of conversions between heat and other forms of energy.  James Prescott joule is usually given the credit for discovering the First Law of Thermodynamics.  The First Law of Thermodynamics states that the energy is conserved. Internal energy (U) of a system changes from an initial value to a final value due to Heat (Q) minus Work (W).

Second Law of Thermodynamics  The second law states that Heat Flows Spontaneously from a Substance at a Higher Temperature to a Substance at a Lower Temperature and Does Not Flow Spontaneously in the Reverse Direction unless work is done.  2:11

From Order to Disorder The second law also shows that all systems naturally tend toward disorder. Entropy is a Measure of the Disorder of a System. Work is required to maintain or increase order. Thermal energy that is not converted into work is called waste heat. A heat engine is a device that converts thermal energy into work. A heat engine can do work only if some waste heat flows to a colder environment.  2:15  5:06 Asylum

Third Law of Thermodynamics  The third law of thermodynamics states that absolute zero cannot be reached. All matter has kinetic energy within it because its particles will always be moving.  Absolute zero would be the state at which the molecules in a substance do not move at all. This has never happened.  1:35  3:07

Conclusion The first law of thermodynamics states that energy is conserved. The second law of thermodynamics states that thermal energy can flow from colder objects to hotter objects ONLY if work is done on the system. The third law states that absolute zero cannot be reached.