Heat

1
Heat Temperature

• Concept Summary
• Batesville High School Physics

2
Historical Heat

• As late as 200 years ago, heat was regarded as a
  fluid, called caloric.
• It was believed that this caloric fluid flows
  from hot objects to cold objects.

3
Historical Heat

• The scientific study of heat was motivated by the
  Industrial Revolution with its use of steam
  engines and machines.
• In the 19th century, James Prescott Joule (and
  others) showed that heat is a form of energy.

4
Heat Terms

• Actually, thermal energy is only called heat when
  it is moving between objects.
• Heat transfers thermal energy from one object to
  another (like work).
• Energy inside an object is properly called
  internal energy - the kinetic and potential
  energy of its particles.

5
Adding Heat

• So, when heat energy is transferred to an object,
  the energy shows up as kinetic energy
  potential energy of the objects particles
  (atoms, molecules, etc.)

6
Temperature

• An objects temperature is related to the average
  kinetic energy of the particles in an object.
• Higher average KE means higher temperature.

7
Moving Heat Energy

• Heat energy flows from an object at higher
  temperature to an object at lower temperature -
  if the objects are in thermal contact.
• (To make energy move the other way, you have to
  do work.)

8
Thermal Equilibrium

• Heat energy will flow until the two objects
  reach the same temperature - they are then in
  thermal equilibrium.

9
The Lowest Temperature

• Since there is a minimum kinetic energy for
  particles (0 J), there is a lowest possible
  temperature absolute zero.
• Scientists have produced temperatures within a
  small fraction of a degree of absolute zero.

10
Temperature Units
Name Water freezes Room Temp. Water boils Absolute Zero
Fahrenheit 32o 70o 212o -459.7o
Celsius 0o 21o 100o -273.15o
Kelvin 273.1 294 373.1 0
11
Temperature is NOT Heat

• An object may have a relatively high temperature
  and a relatively low internal energy.
• An object may have a relatively low temperature
  and a relatively high internal energy.

12
Temperature is NOT Heat

• It is possible for heat to flow from an object
  with very little energy (but high temperature) to
  an object with lots of energy (but low
  temperature).

13
Temperature and Heat

• When you add heat energy to an object, its
  temperature may (or may not!) increase.

14
Measuring Heat Energy

• Since heat is energy, it can be measured in
  Joules.
• A common (and old-fashioned) unit of heat energy
  is the calorie.

15
The calorie the Calorie

• 1 calorie is the amount of heat needed to raise
  the temperature of water by 1oC.
• 1 Calorie 1 kilocalorie 1000 calories
• The Calorie is the diet calorie.

16
Specific Heat Capacity

• 1 calorie of heat will raise the temperature of
  different substances by different amounts.
• The amount of heat energy required to raise the
  temperature of a substance by 1oC is called the
  specific heat capacity, or specific heat.

17
Specific Heat of Water

• By definition, the specific heat of water is 1.
• This is a high specific heat, meaning it takes a
  relatively large amount of energy to raise the
  temperature of water water holds a lot of
  energy.

18
Calculating Heat Energy

• The amount of heat energy needed to raise the
  temperature of a a substance depends on
• The amount of the substance
• The specific heat of the substance
• The change in temperature

19
Calculating Heat Energy

• H mcDT
• where
• H heat energy added/removed
• m mass
• c specific heat
• DT change in temperature

20
Moving Heat Energy

• Since heat is energy, heat can be conserved in an
  isolated system.
• In a 2-object system
• Heat lost by object A heat gained by object B
• mAcADTA mBCBDTB

21
The End