Temperature in Thermal Systems

1.4.11.4.1

Objectives

• Define thermal energy.Define thermal energy.• Name the property of a body that determines its Name the property of a body that determines its

temperature.temperature.• Given Celsius or Fahrenheit temperatures and the Given Celsius or Fahrenheit temperatures and the

formula for conversion, find the equivalent formula for conversion, find the equivalent temperature on the alternate scale.temperature on the alternate scale.

• Explain the difference between heat and thermal Explain the difference between heat and thermal energy.energy.

Work and Energy

• Work on an object can change its position or Work on an object can change its position or speed.speed.

• EnergyEnergy – property that enables an object to do – property that enables an object to do work.work.• Increasing energy doing work:Increasing energy doing work:

• hammer by lifting.hammer by lifting.• gas by compressing.gas by compressing.• recharging a battery by forcing electrons in recharging a battery by forcing electrons in

the reverse direction.the reverse direction.

Forms of Energy

• Potential energyPotential energy – a change in position can – a change in position can cause an body to gain energy resulting in a cause an body to gain energy resulting in a potential to do work.potential to do work.

• Kinetic energyKinetic energy – the energy of motion; an – the energy of motion; an body in motion has the ability to do work.body in motion has the ability to do work.

• KE as a model of random motion of atoms and KE as a model of random motion of atoms and molecules.molecules.• Rate of this motion determines state of matter.Rate of this motion determines state of matter.

• Thermal motionThermal motion – random motion of an objects – random motion of an objects atoms and molecules.atoms and molecules.

• Thermal energyThermal energy – total energy of the thermal – total energy of the thermal motion of motion of allall particles that make up an object. particles that make up an object.

Temperature

Less thermal energy More thermal energy

Thermal energy always flows from “hotter” to “colder” bodies.

• TemperatureTemperature – measure of the average – measure of the average kinetic energy of thermal motion in an kinetic energy of thermal motion in an object.object.

• Size of pie and thermal energy and average Size of pie and thermal energy and average thermal motion (KE; see p. 66)thermal motion (KE; see p. 66)

Measuring Temperature• Thermal energy, as all forms of energy, is Thermal energy, as all forms of energy, is

measured in Joules (J).measured in Joules (J).• Temperature is measured in degrees.Temperature is measured in degrees.• ThermometerThermometer – device used to measure – device used to measure

temperature; uses the expansion and contraction of temperature; uses the expansion and contraction of a liquid, usu. colored alcohol or mercury (Hg).a liquid, usu. colored alcohol or mercury (Hg).

• Thermal equilibrium – when the average Thermal equilibrium – when the average KE between to bodies is equal.KE between to bodies is equal.

Temperature Scales

)32(9

5 FC TT

325

9 CF TT

To convert from Fahrenheit to Celsius:

To convert from Celsius to Fahrenheit:

Heat

• HeatHeat – – QQ, the energy that flows from one object to , the energy that flows from one object to another because of a temperature difference.another because of a temperature difference.• Again from higher avg. KE to lower avg. KE.Again from higher avg. KE to lower avg. KE.• Not another word for thermal energy.Not another word for thermal energy.• Thermal energy in transit; measured also in Joules Thermal energy in transit; measured also in Joules

(J).(J).• Three ways in which heat is transferred:Three ways in which heat is transferred:

• ConductionConduction• ConvectionConvection• Radiation Radiation

• The greater the The greater the temperature differencetemperature difference between two bodies in contact, the greater between two bodies in contact, the greater the heat transferred.the heat transferred.• Prime mover in thermal systems.Prime mover in thermal systems.

Exercises

• Answer 1-12, pp. 76-78.Answer 1-12, pp. 76-78.