Transcript Temperature in Thermal Systems

Temperature in Thermal Systems
1.4.1
Objectives
• Define thermal energy.
• Name the property of a body that determines its
temperature.
• Given Celsius or Fahrenheit temperatures and the
formula for conversion, find the equivalent
temperature on the alternate scale.
• Explain the difference between heat and thermal
energy.
Work and Energy
• Work on an object can change its position or
speed.
• Energy – property that enables an object to do
work.
• Increasing energy doing work:
• hammer by lifting.
• gas by compressing.
• recharging a battery by forcing electrons in
the reverse direction.
Forms of Energy
• Potential energy – a change in position can
cause an body to gain energy resulting in a
potential to do work.
• Kinetic energy – the energy of motion; an
body in motion has the ability to do work.
• KE as a model of random motion of atoms and
molecules.
• Rate of this motion determines state of matter.
• Thermal motion – random motion of an objects
atoms and molecules.
• Thermal energy – total energy of the thermal
motion of all particles that make up an object.
Temperature
Less thermal energy
More thermal energy
Thermal energy always flows from “hotter” to “colder” bodies.
• Temperature – measure of the average
kinetic energy of thermal motion in an
object.
• Size of pie and thermal energy and average
thermal motion (KE; see p. 66)
Measuring Temperature
• Thermal energy, as all forms of energy, is
measured in Joules (J).
• Temperature is measured in degrees.
• Thermometer – device used to measure
temperature; uses the expansion and contraction of
a liquid, usu. colored alcohol or mercury (Hg).
• Thermal equilibrium – when the average
KE between to bodies is equal.
Temperature Scales
To convert from Fahrenheit to Celsius:
5
TC  (TF  32 )
9
To convert from Celsius to Fahrenheit:
9
TF  TC  32
5
Heat
• Heat – Q, the energy that flows from one object to
another because of a temperature difference.
• Again from higher avg. KE to lower avg. KE.
• Not another word for thermal energy.
• Thermal energy in transit; measured also in
Joules (J).
• Three ways in which heat is transferred:
• Conduction
• Convection
• Radiation
• The greater the temperature difference
between two bodies in contact, the greater
the heat transferred.
• Prime mover in thermal systems.
Exercises
• Answer 1-12, pp. 76-78.