1. Energy: Thermal

2. Objectives
 Learn the formula for calculating Heat Energy
 Evaluate social, economic, and
environmental issues related to thermal
energy
 Learn the differences in heat transfer.
 Conduction, Convection, Radiation

3. Energy (Thermal): Main Ideas
 Work and thermal energy are often related. When mechanical, fluid or
electrical work is done, part of the work turns into heat energy. Heat energy
can also be used to do work (steam engines and internal combustion
engines).
 There is a direct relationship between heat energy and mechanical energy.
This relationship is called “the mechanical equivalent of heat”.
 Heat energy always moves from hot objects to cold objects. The heat
gained or lost by an object can be calculated using the formula, H = mcΔT
 Heat moves from hot objects to cold objects in three processes:
conduction, convection and radiation.
 Heat energy losses prevent 100% efficiency in useful energy conversions.
When mechanical work is done (measured in Joules), some of this work is
used to overcome resistance. This produces heat energy which is
measured in BTUs or Calories. There is a direct conversion from
mechanical work to heat energy which is referred to as the mechanical
equivalent of heat.
Mechanical Energy Expended
Mechanical Equivalent of Heat = Heat Energy Produced when all
mechanical energy goes into heat energy

4. Processes for transferring Heat Energy
 Conduction: Heat energy is transferred from a hot region to a cooler region
by vibrating molecules or atoms.
 Convection: An air mass or volume of fluid is used as a medium by which
heat energy is transferred.
 Radiation: Movement of heat energy by electromagnetic waves. Radiation
may be visible (red hot piece of steel), or invisible (infrared radiation from
the sun).

5. Heat energy gained or lost

6. Heat Energy Applications

7. Current Projects
Ivanpah, California

8. Using Solar Energy for Heat
Societal Context:
Millions of people get sick every year
from drinking contaminated water.
An estimated 1.5 billion people get
diarrhea because of bad water and from
that 2 million deaths occur. Billions of
people worldwide don’t have access to
clean water that we enjoy, and
infrastructure doesn’t exist to allow
access to clean water.

9. Making use of Solar Energy
These populations do
however have plenty of
sun, that can be used
for free energy. Solar
ovens can not only
cook food, but can kill
harmful microbes that
cause illness and
death.

10. Water Pasteurization
Louis Pasteur
discovered the science
of killing harmful
pathogens and we
know it now as
pasteurization; the
killing of disease-
causing contaminants
in food.

11. Practice Problem
How much heat energy is required to pasteurize
1 Liter of water that is originally 10˚C?
specific heat of water (c) = 4.186 J/g•˚C
water pasteurization = 65˚C
formula: H=mc∆T
H=(1000g)(4.186J/g•˚C)(55˚C)
H=230,230 Joules

12. Practice Problem
How much heat energy is required to heat a
can of chili (3.06kg) from 21˚C to boiling point
(100˚C) c of chili is 5.128 J/g•˚C
H=mc∆T
H=(3060g)(5.128 J/g•˚C)(79˚C)
H=1,239,642.72Joules
H=1.239MJ

13. Solar Oven Challenge
 Engage in cooperative learning to create a
solar oven that can pasteurize water and
cook food
 Create an oven that is inexpensive to build
and that can be easily transported and stored
 Conduct experiments that test the
effectiveness of your constructed oven

14. Divide into teams
 Get into teams of 3-4 people
 Read the instruction packet
 Timeline: 2 full class days to construct.
 Should be finished by next weekend. Use RTI
if more time is needed
 School-wide Physics Class Potluck April 16
during lunch
 You can conduct research to help you find a
good oven design, so you don’t have to start
from scratch