Announcements
Today we will do:
• Exam I is one week from tomorrow (Oct. 14)
– Covers everything in text up to “Power”-what we
finished last week: Ch. 1 through Ch. 5.5
– Formula sheet: Both sides of a single, letter sized
(8.5”x11”) paper in your own handwriting, no copies, no
printed material. You can even write down entire
problems provided they are in your own handwriting.
– Calculator: All calculators allowed provided they are
NOT communication devices.
– Room assignments will be posted on web.
– Last year’s Exam I with solutions will also be posted on
web.
Nonconservative Forces and Energy
Wnc = ( KEf − KEi ) + (PEi − PEf )
Wnc
or
= (KEf + PEf ) − (KEi + PEi )
The energy can either cross a boundary or the
energy is transformed into a form of nonmechanical energy such as thermal energy
(friction or direct collisions)
•
•
•
•
Energy Transformations
Power
Examples
Fuel
Transferring Energy
• By Work--applying a force--Produces displacement
of the system
• Heat--The process of transferring
heat by collisions between molecules
• Mechanical Waves--disturbance
propagates through a medium
Examples include sound, water,
seismic, electricity
• Electromagnetic radiation--electromagnetic waves
Light, microwaves, radio waves, gamma rays,
X-rays
Energy and Quantum Mechanics
Schroedinger’s Equation = Conservation of Energy
( KE + PE )ψ = Eψ where ψ(r) is the wave function
Predicts shapes of electron clouds around nuclei in atomswhat you learned in chemistry
Why was energy a good concept to learn?
Because it was conserved.
Physicists love conservation
(KE + PE) is conserved. KE =
PE is electrostatic (PHY2054)
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Grand Statement:
Conservation of Energy
Power
• We can neither create nor destroy energy
– Another way of saying energy is conserved
– If the total energy of the system does not remain
constant, the energy must have crossed the boundary by
some mechanism
– Applies to the whole universe and everything that
happens in it
• The rate at which energy transfer takes
place
Work F ∆x
P =
=
= Fv
∆t
∆t
• SI units are Watts W =
J kg m2
=
s
s23
• Motors (US) 1 hp = 550 ft lb = 746 W
s
There is only one Universe by the observation of
Conservation of Energy
Table 5.1, p. 147
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