Heat CapacityHeat Capacity

Work InWork In

The work - energy principle The work - energy principle applies to all objects.applies to all objects.

• If an object speeds up it If an object speeds up it gains kinetic energy.gains kinetic energy.

• If an object slows down it If an object slows down it loses kinetic energy.loses kinetic energy.

211 )2/1( mvK

Work done on a system

v2v1

222 )2/1( mvK

KW

Heat InHeat In

Temperature change is due Temperature change is due to heat (Q).to heat (Q).

• If an object’s temperature If an object’s temperature increases it gains heat.increases it gains heat.

• If an object’s temperature If an object’s temperature decreases it loses heat.decreases it loses heat.

11,UT

Heat into a system

22 ,UT

TQ

Heat CapacityHeat Capacity

The ratio of the change in heat to the change in The ratio of the change in heat to the change in temperature is the temperature is the heat capacity heat capacity (C).(C).• Depends on materialDepends on material• Depends on the massDepends on the mass• Measured in J/KMeasured in J/K

TCQ

Specific HeatSpecific Heat

The ratio of the change in The ratio of the change in heat to the change in heat to the change in temperature is the temperature is the heat heat capacity capacity (C).(C).• Depends on materialDepends on material

• independent of the massindependent of the mass

• Measured in J/kg-KMeasured in J/kg-K

MaterialMaterial Specific heatSpecific heat

MercuryMercury 140 J/kg-K140 J/kg-K

CopperCopper 390 J/kg-K390 J/kg-K

SteelSteel 500 J/kg-K500 J/kg-K

GraniteGranite 840 J/kg-K840 J/kg-K

AluminumAluminum 900 J/kg-K900 J/kg-K

WoodWood 1400 J/kg-K1400 J/kg-K

IceIce 2100 J/kg-K2100 J/kg-K

WaterWater 4200 J/kg-K4200 J/kg-KTmcQ

Take a ShowerTake a Shower

You are last to use the You are last to use the shower today and the shower today and the temperature in the water temperature in the water heater has dropped to 18 heater has dropped to 18 C C from the normal temperature from the normal temperature of 50 of 50 C. The heater holds C. The heater holds 150 kg and has a 50 kW 150 kg and has a 50 kW heating coil.heating coil.

How long should you wait How long should you wait before starting your shower?before starting your shower?

Find the heat required.Find the heat required. QQ = = mcmcTT = (150 kg) = (150 kg)

(4200 J/kg-K) ( 32 C)(4200 J/kg-K) ( 32 C) QQ = 2.1 x 10 = 2.1 x 1077 J J

Find the time from the Find the time from the power, and set the heat to power, and set the heat to the work.the work. PP = = WW//tt tt = = QQ / / PP (2.1 x 10(2.1 x 1077 J) / (5 x 10 J) / (5 x 1044 W) W) tt = 4000 s = 1.1 hr = 4000 s = 1.1 hr

Equilibrium TemperatureEquilibrium Temperature

Two systems in thermal contact will adjust to reach Two systems in thermal contact will adjust to reach the same temperature - thermal equilibriumthe same temperature - thermal equilibrium

If they are thermally insulated, all the heat goes from If they are thermally insulated, all the heat goes from the hot system to the cold system.the hot system to the cold system.

1 2 0222111 TcmTcm

Doing DishesDoing Dishes

A 1.5 kg aluminum pan is A 1.5 kg aluminum pan is heated to 180 heated to 180 C then placed C then placed into a sink with 8 kg water at into a sink with 8 kg water at 20 20 C.C.

If no water boils, what is the If no water boils, what is the equilibrium temperature?equilibrium temperature?

Setup the equation for an Setup the equation for an unknown equilibrium unknown equilibrium temperature temperature TT..

Solve for Solve for TT..

T = 26 T = 26 CC

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