1. 16.2 Heat and Thermodynamics Conduction Conduction is the transfer of thermal energy with no overall transfer of matter. Conduction in gases is slower than in liquids and solids because the particles in a gas collide less often.

2. 16.2 Heat and Thermodynamics Conduction occurs within a material or between materials that are touching. In conduction, collisions between particles transfer thermal energy, without any overall transfer of matter. A thermal conductor is a material that conducts thermal energy well. A material that conducts thermal energy poorly is called a thermal insulator. Conduction

3. 16.2 Heat and Thermodynamics The arrows show how thermal energy is conducted away from the heat source in a metal frying pan. Conduction

4. 16.2 Heat and Thermodynamics Metals are good thermal conductors. –When a frying pan is on a hot stove, the bottom of the metal pan heats first and the metal handle last. The flames do not directly heat the handle. –Tile is a better conductor than wood. A tile floor feels colder than a wooden floor when both floors are at room temperature. The tile transfers thermal energy more rapidly away from your skin. Air is a very good thermal insulator. –Wool garments and plastic foam cups use trapped air to slow down conduction. Conduction

5. 16.2 Heat and Thermodynamics Convection Convection is the transfer of thermal energy when particles of a fluid move from one place to another. Convection currents are important in many natural cycles: ocean currents weather systems movements of hot rock in Earth’s interior

6. 16.2 Heat and Thermodynamics A.Passing sandbags along a line is like transferring thermal energy by convection. B.The arrows show convection of air in an oven. Convection

7. 16.2 Heat and Thermodynamics A convection current occurs when a fluid circulates in a loop as it alternately heats up and cools down. Air at the bottom of an oven heats up, expands, and becomes less dense. The hot air rises. Rising hot air cools as it moves away from the heat source. As a result, the coolest air is at the top of the oven. Convection

8. 16.2 Heat and Thermodynamics Radiation Radiation is the transfer of energy by waves moving through space. All objects radiate energy. As an object’s temperature increases, the rate at which it radiates energy increases

9. 16.2 Heat and Thermodynamics When you stand to the side of a charcoal grill, heat reaches you without convection or conduction. The sun warms you by radiation on a clear day. The space between the sun and Earth has no air to transfer thermal energy. Heat lamps used in restaurants are another example of radiation. Radiation

10. 16.2 Heat and Thermodynamics The heating coil on a stove radiates thermal energy. The changing color of the red arrows indicates that the farther you are from the coil, the less radiation you receive. Radiation

11. 16.2 Heat and Thermodynamics The study of conversions between thermal energy and other forms of energy is called thermodynamics. James Prescott Joule measured the energy changes in a system (a group of objects that interact with one another). –Joule's system included a falling weight turning a paddle wheel in water. – Joule found that the work done by the falling weight almost exactly equaled the thermal energy gained by the water. – He is given credit for discovering the 1 st law of thermodynamics Thermodynamics

12. 16.2 Heat and Thermodynamics The first law of thermodynamics states that energy is conserved. Energy cannot be created or destroyed, but it can be converted into different forms. Added energy increases the thermal energy of a system or does work on the system. In either case, energy is conserved. Thermodynamics First Law of Thermodynamics

13. 16.2 Heat and Thermodynamics Pushing on the pump does work on the system. – Some of the work is used to compress air into the tire – Some is converted into thermal energy, which heats the air in the pump and the tire. Thermodynamics

14. 16.2 Heat and Thermodynamics The second law of thermodynamics states that thermal energy can flow from colder objects to hotter objects only if work is done on the system. Thermodynamics Second Law of Thermodynamics Thermal energy flows spontaneously only from hotter to colder objects. A refrigerator must do work to transfer thermal energy from the cold food compartment to the warm room air. The thermal energy is released by coils at the bottom or in the back of the refrigerator.

15. 16.2 Heat and Thermodynamics Heat engine: any device that converts heat into work The efficiency of a heat engine is always less than 100%. Thermal energy that is not converted into work is called waste heat. Waste heat is lost to the surrounding environment. Thermodynamics

16. 16.2 Heat and Thermodynamics The third law of thermodynamics states that absolute zero cannot be reached. Third Law of Thermodynamics The efficiency of a heat engine increases with a greater difference between the high temperature inside and the cold temperature outside the engine. A heat engine could be 100 percent efficient if the cold outside environment were at absolute zero (0 Kelvin). This would violate the third law of thermodynamics.