Chapter 21: Temperature, Heat, and Expansion

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

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

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

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

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

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

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

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

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

Controlling world climates Deserts Why are summer & winter late? Why do people want to live in California? Deserts – hot during day – cold @ 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

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

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

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 -