Heat & Temperature

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

6. Temperature • An object’s 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

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