Chapter 13: Heat and Temperature

1. Chapter 13: Heat and Temperature Section 1 – Measuring Temperature

2. What is temperature? • Generally, temperature is a measure of how hot or cold something is • Scientifically… • Definition: temperature – a measure of the average KE of particles. • The particles of ALL matter are constantly moving and vibrating.

3. What is temperature? • If we could look at the atoms & molecules of hot air, we would see… • The molecules would be moving very fast! • Hot substances have faster moving particles.

4. What is temperature? • If we could look at the atoms & molecules of cold air, we would see… • The molecules would be moving very slowly! • Cold substances have slow moving particles. Even the particles of ICE are moving…just really slowly.

5. When the temperature of an object changes, thermal energy is being transferred. Imagine that you are holding a piece of ice in your hand. What happens to the ice? The ice melts, of course, but what happens in scientific terms…?

6. Your hand is much warmer than the ice. That means that it has more kinetic energy. As you hold the ice in your hand, thermal energy is transferred from your hand to the ice.

7. Temperature & Energy Transfer As a result, the molecules in the ice move faster… And their kinetic energy increases, which causes the ice to melt. • Definition: heat – the energy transferred between objects with different temperatures.

8. Thermal energy always flows from hot to cold. “Things that are hot, flow to where it is not.”

9. Measuring Temperature • Definition: thermometer – a device used to measure the temperature of an object. • In a typical thermometer, a liquid expands when heated and contracts when cooled. • The level of the liquid can be read to find the temperature.

10. Temperature Scales • In the United States, the Fahrenheit scale is used to measure temperature. • The physicistDaniel Gabriel Fahrenheit developed the scale in 1724. • Today, only a few countries still use the Fahrenheit scale.

11. Temperature Scales • In 1742, Anders Celsius created the Celsius temperature scale. • The scale uses 0 as the freezing point of water and 100 as the boiling point. • Celsius is used most commonly throughout the world as a means for measuring temperature.

12. Temperature Scales • In 1848, physicist William Kelvin created the Kelvin temperature scale based on “absolute zero”. • Definition: absolute zero – the theoretical temperature at which matter has 0 KE. It is the coldest temperature possible. • Kelvin (K) is the SI unit for temp. • It doesn’t use negatives! • This makes it perfect for calculations. Absolute zero is -273 degrees Celsius. Or -459 degrees Fahrenheit….BRRR.

13. Radiation Chapter 13: Heat & Temperature Convection Section 2: Energy Transfer Conduction

14. Definition: thermal conduction – thermal energy transfer between objects in direct contact. • It occurs as fast moving particles collide with slower moving particles.

15. Some materials can transmit energy better than others. Definition: thermal conductor – a substance that easily transmits thermal energy. Most metals are very good conductors of thermal energy.

16. Other materials do not conduct thermal energy very well at all. Definition: thermal insulator – a substance that does not transmit thermal energy well. Some examples of insulators: Glass Wood Rubber Cloth

17. Definition: convection – the transfer of thermal energy through moving fluids. Convection occurs in the atmosphere, and also in the ocean. It even occurs in our bodies.

18. Convection Currents • Convection currents are “rivers” of moving fluids due to temperature differences. They transmit warmer/cooler air throughout your home.

19. The oceans also contain convection currents!

20. Definition: radiation – thermal energy transferred as electromagnetic waves. (Radiant Energy) • Sunlight and infrared waves are examples of radiation.

21. Radiation does not require matter in order to transmit energy. • When you are near an oven, you can feel the heat of the oven without touching it. • This is an energy transfer due to radiation. • Radiation is the only type of energy transfer that can occur through space.

22. Chapter 13: Heat & Temperature Section 3: Using Heat

23. Using Heat: Biology How heat is related to living things? • Our bodies maintain a constant temperature of 98.6 ºF. • It takes energy to keep a body at this temperature! So, where does the energy come from?

24. Using Heat: Biology Remember that food is an example of chemical energy? • The body converts chemical PE into thermal energy in order to keep a constant temperature. • The blood flow in your body transports heat to different areas, through convection. Via the circulatory system…

25. Coooold… • If the body is exposed to cold conditions for too long, it will lose more thermal energy than it produces. • Hypothermia occurs when your body temp. falls below normal.

26. Fever • If the body’s temperature rises above normal, it experiences fever. • If it gets too hot, the body can overheat, causing organs to shut down.

27. Internal Air Conditioning • Sweat is produced in order to cool the body through evaporation. • The skin becomes covered with sweat… • It absorbs thermal energy from our body, and evaporates… • Leaving our body cooler in the process!

28. Heat & Technology One of the major uses of heat is air conditioning! • Definition: air conditioning system - a machine used to transfer thermal energy into or out of an area.

29. Refrigerants • Ever wondered how a refrigerator works? • Definition: refrigerant – a substance that is used to cool an area by evaporation. • A refrigerant can easily absorb thermal energy and evaporate. Refrigerators use refrigerants in order to cool the inside.

30. Refrigerators • A refrigerant absorbs thermal energy in order to evaporate. • Evaporation causes the air to cool.

31. Heat Engines • Heat engines are our major source of travel…what is a heat engine? • Definition: heat engine – a device that converts chemical PE into thermal energy, then into mechanical energy. Internal Combustion Engine