1. Chapter 21: Temperature, Heat, and Expansion

2. Temperature
Temperature is a measure of the avg KE of particles in the substance
Three Scales used
Celsius
Fahrenheit
Kelvin
Thermometers detect KE
Talk about origin of 3 temperature scales – Fahrenheit created a salt water bath (coldest thing he could) – set that as zero
Celsius – based on water – like most metric- makes our life easy – was called centigrade – 100 degrees
Kelvin – best scale – uses real definition of temperature – 0 Kelvin in no KE in particles

3. High Quality H2O Water boils at Water Freezes at 100oC 212oF 373 K 0oC
Need to memorize these 6 values – then can convert anything

4. Absolutely Cool Absolute Zero
Temperature at which KE is no longer present
0 K = -273oC
Unreachable – Measuring temperature adds KE
Calculated it by extrapolating data

5. Is It Getting Hot in Here
Matter contains energy, not heat
Paperclips
HEAT is : Energy that is transferred from high temperature substances to low temperature substances
Hand out paperclips – twist back & forth till it breaks – hold end – its hot!
KNOW THIS DEFINITION!!!!
Like water flowing downhill – energy flows from hot to cold

6. Let’s Turn Up the Heat
Thermal Contact: energy flow from one object to another when touching
Thermal Equilibrium: two objects in contact have the same temperature
NATURE LIKES EQUILIBRIUM!!!
Contact – heat can flow – touching
When you are not sure what will happen – assume system will move toward equilibrium

7. Measurement of Heat Heat is measured in calories Joules – SI unit
A calorie is the amount of energy needed to raise 1 g of water 1o C
Joules – SI unit
1 calorie = 4.18 Joules
Food calories are ‘C’alories – 1000 science calories

8. Let’s Be More Specific
Specific Heat capacity is quantity of heat needed to raise temperature of one gram by 1oC
Different substances have different specific heats
Q=mcΔT
Some things are harder to heat than others – Way to remember - examples – M-cat

9. Practice with the Q= mcΔT
How much energy is needed to heat 46 grams of water 30.0 degrees? Specific heat of water is 1 cal/g°C
How much will 500. calories of energy raise the temperature of a 65 gram mass of iron? Specific heat of iron is .11cal/g°C
6000. Joules changed the temperature of a container of water 40.0°C. What is the mass of the water? Specific heat of water 4.18 Joules/g°C
1380 calories
70 C
35.9 grams

10. Water Water Everywhere
Water has a very high specific heat capacity
Advantages
Useful for cooling
Useful for warming
Holds a lot of energy in its temperature
U of I – chilled water cooling – send cold water out in summer – heat of air absorbed into it
Hot water heat – same idea – opposite direction – house I grew up in – this building – hot water bottle in bed
Cars use ‘coolent’ to remove heat from the engine – basically water- talk about anti-freeze later

11. Controlling world climates
Deserts
Why are summer & winter late?
Why do people want to live in California?
Deserts – hot during day – night – sand has low capacity – water high
Thermal Lag – water on earth takes time to warm up/cool down – swim in August, not June, cold in February, not December
Live by a big ocean – California & Florida & England mild – Middle of Continent is hot & cold – kansas – cooler by the lake - Chicago

12. Let’s Expand Our Horizons
Most matter expands when heated
Gases fastest, then Liquids then Solids
Hot-air balloons
Ring & Sphere demo
Bi-metal strip
Thermal rate of expansion
Hot air balloons – air spreads out, less dense – weight is less – buoyancy overcomes
Bi-metal strip – different things different coefficents of expansion

13. Expansion examples How thermostats work Railroads, power lines
Bridge joints
Thermal pipe joints
Show example of thermostat – basicly long piece of metal
Why railroads are built like they are – click-clack

14. Exceptions to the Rule Water is different from other substances
Water expands when temperature is above or below 4oC
Water is smallest and most dense at 4oC
This is why Ice floats – draw graph of density vs. Temperature -