Common Rocks
|o an Earth scientist, rocks represent much " more than usable substances. They are the materials of the Earth; understanding their origin and how they change allows us to begin to un derstand Earth and its processes. It is often said that "t
EAS 375
Fall 2010
Lecture questions - Energy
1. There have been a series of energy crises in the past. What were the causes
of these crises?
-1st: Diminishing availability of wood in England in the 12 century.
-alternative was coal.
-2nd: Decline in sperm
iClicker
! Lecture will start with iClicker question
! 5 lectures (2 1/2 weeks) are discarded,
including todays
! 100pt out of 700 total.
5
Thursday, August 26, 2010
Count # of equations and unknown (should be equal!)
T sin = Fc
T cos = Fg
Fg = mg
5=5
2
q
Fc = k 2
d
d/2
sin =
l
eliminate T
eliminate d
74
Thursday, August 26, 2010
Cell phones
! Turn it off.
! If recurring problem, we will introduce a rule If it
rings: you leave the class for the whole lecture.
4
Thursday, August 26, 2010
Count # of equations and unknown (should be equal!)
T sin = Fc
T cos = Fg
Fg = mg
5=5
2
q
Fc = k 2
d
d/2
sin =
l
eliminate d
74
Thursday, August 26, 2010
Highlights
!
http:/www.physics.purdue.edu/academic_programs/courses/phys241/
! Grades In Blackboard
! Register I-Clicker in Blackboard (before the end of term)
! Do Reading Assignments for Lecture
! Complete Homework by 7:00 AM Mondays and
Wednesdays
! Ho
! All administrative/Blackboard/iClicker/
CONNECT PLUS/attendance/scores questions
should be directed to David Koltick,
koltick@purdue.edu
2
Thursday, August 26, 2010
Example - Charged Balls
!
Simplify
!
We divide the two free-body force equations
containing the string tension
!
Thus we eliminate the string tension and get
!
Putting in our expressions for the force of gravity and
the electric force, we get
49
Thursday,
Example - Charged Balls
!
Simplify
!
We divide the two free-body force equations
containing the string tension
!
Thus we eliminate the string tension and get
!
Putting in our expressions for the force of gravity and
the electric force, we get
49
Thursday,
Action at distance: through fields
Charges produce fields, fields act on other charges
another charge
electric eld
electric charge (source of eld)
4
Thursday, August 26, 2010
Action at distance: through fields
Charges produce fields, fields act on other charges
electric eld
electric charge (source of eld)
4
Thursday, August 26, 2010
The Four Forces
! The four fundamental forces work by exchanging
elementary particles (not necessarily real, might be
virtual).
Electromagnetic - photon
Weak - W and Z bosons (observed in 1983)
Strong gluons (observed in 1979)
Gravity - graviton (?) (
Fundamental Forces of Nature
! Unification of forces?
! E.g., electricity and magnetism were thought
different, but actually are two sides of
the same force
! EM & weak forces are also united - electroweak
! Some ideas how to unite electroweak & strong
!
Example - Charged Balls
!
Consider two identical charged balls hanging from the
ceiling by strings of equal length = 1.5 m (in
equilibrium). Each ball has a charge of q=25 C. The
balls hang at an angle ) = 25 with respect to the
vertical. What is the mass
Example - Charged Balls
!
Consider two identical charged balls hanging from the
ceiling by strings of equal length = 1.5 m (in
equilibrium). Each ball has a charge of q=25 C. The
balls hang at an angle ) = 25 with respect to the
vertical. What is the mass
Problem Solving Strategy
1. THINK
Read the problem carefully. Ask yourself what quantities are known, what quantities might
be useful but are unknown, and what quantities are asked for in the solution.
2. SKETCH
Make a sketch of the physical situation to
General Problem Solving Strategies
1.
2.
3.
4.
5.
6.
Write what is given.
Sketch
Write equations
Count # of equations and unknown (should be equal!)
Solve the system (DO NOT PLUG IN NUMBERS!)
Check dimensions (if dimensions are wrong, the answer is
wrong)
General Problem Solving Strategies
1.
2.
3.
4.
5.
6.
Write what is given.
Sketch
Write equations
Count # of equations and unknown (should be equal!)
Solve the system (DO NOT PLUG IN NUMBERS!)
Check dimensions (if dimensions are wrong, the answer is
wrong)