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, 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.

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” 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.)

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 NameWater freezes Room Temp. Water boils Absolute Zero Fahrenheit 32 o 70 o 212 o o Celsius0o0o 21 o 100 o o Kelvin

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  T  where:  H = heat energy added/removed  m = mass  c = specific heat   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  T A = m B C B  T B

The End