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.

Thermal energy always flows from “hotter” to “colder” bodies. 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: To convert from Celsius to Fahrenheit:

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.