1. 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

2. 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

3. 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.

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

5. 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.

6. Another way to look at heat transfer

7. 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.

8. Examples of specific heats of different substances

9. 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

10. 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

11. Temperature as a function of heat in water

12. Forms of heat transfer

13. Conduction
Energy of molecules directly transferred to adjoining molecules
Causes them to gain heat

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

15. Conductive heat transfer through a material

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

17. 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

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

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

20. 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

21. 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