Some Basic Concepts of Energy II. Concepts relating to heat Prepared for BIO/EES 105 Energy in our World Kenneth M. Klemow, Ph.D. Wilkes University

Temperature and heat Property of all systems Based on kinetic energy of molecules Heat is TOTAL energy of all molecules in a system Typically measured in Calories or BTUs Temperature is AVERAGE energy of all molecules in a system Typically measured in degrees Fahrenheit Celsius Kelvin Water freezes 32 273 Water boils 212 100 373 Human body 98.6 37 310

Temperature vs heat within and between systems Within a system Increase in heat causes increase in temperature Governed by equation Q = mc(DT) Where: Q – heat (cal., BTU) M – mass C – specific heat DT – change in temp. http://www.thekitchn.com/thursday-giveaway-instantread-56533

Temperature vs heat within and between systems Not related One system can have higher heat yet lower temperature

Temperature vs heat within and between systems Heat can move from one system to another Only when there is a temperature difference Move from higher temperature to lower temperature object. http://www.ces.fau.edu/nasa/

Another way to look at heat transfer http://www.grc.nasa.gov/WWW/Wright/airplane/heat.html

Specific heat (c) Measure of change in temperature as a result of heat absorbed. Metric system: # joules needed to raise 1 kg of material by 1 oC. English system: # BTUs needed to raise 1 lb of material by 1oF. http://addheat.wordpress.com/2011/03/24/

Examples of specific heats of different substances

Heat of vaporization and heat of fusion Involves phase changes solid <-> liquid For water: 80 kcal / kg Vaporization liquid <-> gas For water: 540 kcal / kg http://blogs.yis.ac.jp/19miyoshiay/ http://ww.abc6.com/story/

Heat of vaporization and heat of fusion Heat absorbed or released depending on direction Important in heat balance at earth’s surface, regulating temperatures of organisms

Temperature as a function of heat in water

Forms of heat transfer

Conduction Energy of molecules directly transferred to adjoining molecules Causes them to gain heat http://www.physicstutorials.org/

Conductivity differs among materials High in metals Low in styrofoam Intermediate in brick These make good insulators

Conductive heat transfer through a material

Convection Occurs in liquids and gases Warm liquid / gas becomes less dense and rises through medium Creates eddy currents Carries much energy

Radiation Involves electromagnetic waves Produced by charged particles Travel at speed of light Wave components include: Amplitude Frequency Wavelength Electric and magnetic waves are perpendicular to field of travel

Frequency and wavelength are inversely related Velocity (m/s) = wavelength (m) x frequency (#/second) As wavelength increases, frequency decreases

Radiation is classified by wavelength (and hence by frequency) Less energy More energy

Thought questions When radiation strikes a body, it causes that body to start radiating, itself. Will the wavelengths of that energy likely to be longer or shorter than the energy striking it? When sunlight hits the earth, will the re-radiated energy be more likely to be in the form of: Ultraviolet, Visible, Infrared energy When light strikes a chlorophyll solution, some of the energy is reradiated as visible light. What is the most likely color for that light? Blue, Green, or Red

Need to mention boundary layer effects Conduction, convection and radiation all occur in windless environment. Convection sets up eddies of moving air Adding wind can rapidly remove energy by mass transfer. Objects often covered by boundary layer of still air Conduction and convection predominate Increasing wind speed causes boundary layer to become thinner. Transfer of energy greater when wind increases