Chapter 9

1. Chapter 9 Thermal Energy Presented by April Senger

2. Thermal Energy • Thermal Energy in a substance is the total energy of all it atoms and molecules • It consists of both PE & KE of the particles in the substance • All particles are vibrating Presented by April Senger

3. To distinguish how warm or cold an object is we use temperature The most common temp is measured in Celsius (0 freezing, 37 body temp & 100 boiling) Fahrenheit is common in the US (32 freezing, 98.6 body, & 212 boiling) Kelvin is the SI unit for measuring temp Degrees C and F are not the same size How does a thermometer work? What does that have to do with KE? Temperature Presented by April Senger

4. Concept Check • True or False… • Temperature is a measure of the total kinetic energy in a substance • False…it is the average temperature of the substance Presented by April Senger

5. Absolute Zero • The lower limit of temperature is called absolute zero • This is the temp that theoretically all motion and vibrations would stop = no KE • -273 degrees Celsius is A. Zero • 0 K is also A. Zero • To convert C to K – Add 273 to the temperature in Celsius • This is because C and K have the same size of degree markings • Caution: we do not use the work degree with the Kelvin scale Presented by April Senger

6. Hot Stuff! • Heat is the thermal energy transferred from one substance to another due to a temperature difference between the substances • Substance contain thermal energy NOT heat • Heat is thermal energy that is moving to another object • Thermal energy flows from higher temps to lower temps Presented by April Senger

7. Cool It.. • If you step out of the pool on a 100 degree day, why do you feel cold? • If you feel cold, it is because your thermal energy is leaving your body • Corona of the sun example… Presented by April Senger

8. Concept Check • Suppose you apply a flame to 1 L of water and its temperature rises by 3 degrees C. If you apply the same flame for the same length of time to 3 L of water, by how much will the temp rise? • 1 degree C • When you touch a cold surface, does cold travel from the surface to your hand or does the energy travel from your hand to the cold surface? • It travels from hot to cold. Your hand to the cold surface Presented by April Senger

9. Thermal Expansion • Thermal expansion results from the molecules moving faster and apart in a warm substance • Where might some thing in our society expand or contract? • Bridges, railroads, buildings, dentists • The Law of Conservation of Mass says that matter cannot be created or destroyed • The Law of Conservation of Energy says that energy cannot be created or destroyed Presented by April Senger

10. Concept Check • When you can’t loosen a metal lid on a glass jar, how can you use the concept of thermal expansion to rescue the situation? • Hold it under hot water to expand the lid faster than glass • A Concorde supersonic airplane is 20 cm longer when in flight than when parked on the ground. Why? • Traveling at the speed of sound creates great air friction and heat thus expansion Presented by April Senger

11. What’s Up with Water? • Water does contract until it reaches about 4 degrees C • If forms a unique crystal shape that traps air between the molecules making it less dense • Below 4 degrees C, water begins to expand again • This is why ice floats • Why is it so important that ice floats on our lakes? Presented by April Senger

12. Concept Check • What is the coldest water at the bottom of a frozen lake can be? • 4 degrees C because it is the most dense and will sink towards the rocks • Temps below 4 begin to expand and range up to 0 near the ice Presented by April Senger