Concept Summary Batesville High School Physics

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.

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

.

Heat Terms  Actually,

heat thermal energy

is only called when it is

moving between objects

.



Heat transfers thermal energy

one object to another (like

work

).

from  Energy inside an object is properly called

internal energy potential

- the

kinetic

energy of its particles. and

Adding Heat  So, when heat energy is transferred to an object, the energy “shows up” as

kinetic energy

&

potential energy

of the object’s particles (atoms, molecules, etc.)

Temperature  An object’s

temperature

is related to the

average kinetic energy

of the particles in an object.



Higher average KE means higher temperature.

Moving Heat Energy 

Heat energy “flows” higher temperature

from an object at 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

.)

Thermal Equilibrium  Heat energy will “flow” until the two objects reach the

same temperature

they are then in

thermal equilibrium

.

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.

Temperature Units Name Fahrenheit Water freezes 32 o Room Temp.

70 o Water boils 212 o Absolute Zero -459.7

o Celsius 0 o 21 o 100 o -273.15

o Kelvin 273.1

294 373.1

0

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.

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).

Temperature and Heat  When you

add heat energy

to an object, its temperature

may (or may not!) increase.

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.

The calorie & the Calorie  1

calorie

is the amount of heat needed to

raise the temperature of water by 1 o C

.

 1

Calorie

= 1 kilocalorie = 1000 calories  The Calorie is the “diet calorie”.

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 1 o C

is called the specific heat capacity, or

specific heat

.

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.

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

Calculating Heat Energy  H = mc D T  where:  H = heat energy added/removed  m = mass  c = specific heat  D T = change in temperature

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  m A c A D T A = m B C B D T B

The End