Transcript Slide 1

Review for Test:
velocity=(change in position)/time elapsed
acceleration=change in velocity/time elapsed
Meaning of force:
Total force on an object F= Massx Acceleration
Basic kinds of Force: gravitational and
electromagnetic
Kinetic energy of an object = (1/2)M v2
Gravitational potential Energy= Mgh
Energy is always conserved:
Energy never disappears, though it can change
type.
Thermal Energy
Mechanical Energy
Random atomic
Coherent atomic
motion or displacement motion or displacement
Kinetic and potential
energy
Kinetic and potential
energy
Kinetic energy
per molecule
measured by T
Kinetic energy
=1/2 Mv2
Change in total
thermal energy=
massxspecific heatx
temperature change
Gravitational
potential energy=
Mgh
In the part of the course emphasized in test 2
we emphasized types of conversion of
energy from one form to another:
Mechanical Energy -> Thermal Energy
Thermal Energy -> Thermal Energy
(conduction, convection, radiation)
Thermal Energy -> Mechanical energy
Key points about these are reviewed in the
next panels
Mechanical Energy -> Thermal Energy
(Lab 4, HW 3, Ch 4B-C)
Mechanical Energy is converted to Thermal
energy by the performance of work done
by frictional forces.
Work is the amount of energy transferred =
Fd where F is the part of the force acting
along the direction in which it acts and
d is the distance through which the force acts.
If there is no freezing or boiling, the temperature
rise is related to the thermal energy added by
Thermal energy increase =massx(specific heat)x
temperature increase
Thermal Energy -> Thermal Energy
(Lab 5,6, HW4B,Ch 4D)
Thermal energy change =massx(specific heat)x
temperature increase
Specific heat depends on the kind of material
Energy is conserved in the transfer
If there is boiling or melting then the thermal
energy change (without change In temperature) is
Mass converted from
solid to liquid (in melting)
or from liquid to gas
(in boiling)
X
Latent heat
of melting or
vaporization
Thermal Energy -> Thermal Energy: Modes and
Rates of energy transfer(HW4, Lab5, Ch5,6)
Modes are Conduction, Convection and Radiation
Rate of conduction= (Area x Temperature difference)/R
= Area x( Temperature difference)k/thickness
Thermal Energy ->Mechanical energy
(Lab 7Ch 4EF,Ch 7)
Energy is conserved:
QH=W+QC
Conversion is
never complete:
Efficiency =W/QH <1
Maximum efficiency=(1-TC/TH)