; Quiz 3 830-850am TODAY Have your calculator ready Closed book
Documents
Resources
Learning Center
Upload
Plans & pricing Sign in
Sign Out
Your Federal Quarterly Tax Payments are due April 15th Get Help Now >>

Quiz 3 830-850am TODAY Have your calculator ready Closed book

VIEWS: 0 PAGES: 35

  • pg 1
									Quiz information on the course website
Include :
Quiz answers (posted by ~5pm Tuesdays)
Quiz problems
Quiz rubrics (posted by 5pm following Tuesdays)
Quiz score will also be posted by the end of the
following week.


Quizzes will be returned in your DL section that
meet after the following quiz. (I.e. Quiz3 will be
returned later next week)
What about Quiz 1?              Average 8.69
Those who has not gotten them back will get them in the first
DLM this week. Answer, rubrics are on the course web site.

Request regrade? => Submit your quiz along with Quiz Re-
evaluation Request Form (available from the course
website) to me AFTER the lecture by lecture 6 (Feb12)


What about Quiz 2?
Quiz 2 will be returned in DLM 7 this week.
       Quiz 3 8:30-8:50am TODAY
       Have your calculator ready
              Closed book


          Next lecture February 5
 Quiz 4 will cover the material from today’s
 lecture, FNT’s from DLM 5, material from
DLM6&7 this week, including FNTs for DLM7
         but NOT FNT’s for DLM8.
         Energy systems so far

                                                   Emass-spring
  KE                Etherm         Ebond            Distance from
 Speed                  al         Phase           the equilibrium
                        T                              position


                                PEgra
             Eelectri              v              Enuclea
                c                height                r


Energy is converted from one form to another, but
NEVER created nor destroyed.
If the energy of an object increases, something else must have
given that object its energy.
Conservation of Energy
            Etot = 10 Joule




 5
                              3
                   2



     Nature happens…
Energy Interaction Model
         Etot = 10 Joule




                7
  2                        1
Energy Interaction Model
                Etot = 10 Joule




                         7
  2                                        1


        (-3J) + (+5J) + (-2J) = 0
      ∆Eorange + ∆ Emelon + ∆ Egrape = 0
      Etotal = Eorange + Emelon + Egrape
         Conservation of Energy


FNT 2.1.-1
             Equal mass, identical initial speeds
             Which rock has the greatest speed just
             Before it hits the ground?
              Conservation of Energy
     FNT 2.1.-1

                                         Equal mass, identical initial speeds
                                         Which rock has the greatest speed just
                                         Before it hits the ground?

   Increase in the KE system is the same as the decrease in the PEgrav system
                            ∆PEgravX + ∆ KEX = 0
          (PEgravX)final - (PEgravX)initial + (KEX)final - (KEX)initial = 0
              0           - (PEgravX)initial + (KEX)final - (KEX)initial = 0
            =>
                  (KEX)final = (KEX)initial + (PEgravX)initial

Wait a minute! (KEX)initial = (KEY)initial = (KEZ)initial
                (PEgravX )initial= (PEgravY )initial= (PEgravZ )initial
           Conservation of Energy
  FNT 2.1.-1

                                    Equal mass, identical initial speeds
                                    Which rock has the greatest speed just
                                    Before it hits the ground?

Total energy of the system remains unchanged
                 EtotX = PEgravX + KEX = Constant

How do the total energies of the three rocks compare initially?

                                   Same

How do the total energies of the three rocks compare finally
(or at anytime) ?
                           Same
   Bowling Ball


What is the height of
the bowling ball after one full swing?
           (a) Same
           (b) Higher
           (c) Lower
   Bowling Ball


What is the height of
the bowling ball after one full swing?
           (a) Same
           (Assume friction is negligable)
   Bowling Ball


                        c               a
                               b
When is the speed of the bowling ball
maximum? (a) Starting point

            (b) When rope is vertical
            (c) At point c.
   Bowling Ball


                       c                a
                               b
When is the speed of the bowling ball
maximum?

            (b) When rope is vertical
   Bowling Ball


                         c               a
                                b
When is the PEgravity of the bowling ball
maximum? (a) Starting point

             (b) When rope is vertical
             (c) At point c
   Bowling Ball


                         c            a
                               b
When is the PEgravity of the bowling ball
maximum? (a) Starting point


             (c) At point c.
      Conservation of Energy
    Consider a simple pendulum:
      At the height (peak) of the amplitude, the object is
      at rest. PEgravity = mgh (define h above the low point)

      At the bottom of the motion, the object is moving
      quickly, and h=0. KE = (1/2) m Dv2

    Conservation of Energy dictates that:
              DPEgravity = - DKE
           mgDh = - (1/2) m Dv2
      Etotal = PEgrav + KE = constant
All of the PE goes into KE, and then back again!
Bowling Ball


                                Initial
                    Final
                    (Still in
   KE      PEgrav   motion)
   Speed   Height
Bowling Ball


                    Final
                            Initial

   KE      PEgrav           (In motion)
   Speed   Height
Bowling Ball


                    Initial
                              Final
                              (Still in
   KE      PEgrav             motion)
   Speed   Height
          Potential Energy: Springs
• Springs contain energy when you stretch or compress
them. We will use them a lot in Physics 7.

• The indicator is how much the spring is stretched or
compressed, Dx, from its equilibrium position.

               DPE spring = (1/2) kDx 2
                                                    x
• k is a measure of the “stiffness”
of the spring, with units [k] = kg/s2.

• Dx: Much easier to stretch a spring a little bit than a lot!
  Mass-Spring Systems

DPEmass- spring = (1/2) kDy2 +C
 • k is a property of the spring only
 • PEmass-spring does not depend on mass
 • PE = 0 arbitrary
Mass-Spring Systems


    KE      PEmass-
            spring
    Speed
                  ∆y
Mass-Spring Systems


    KE       PEmass-
    Speed     spring
                ∆y
      Conservation of Energy
      Just like a simple pendulum:
      • At the peak of the amplitude, the object is at
      rest. PEmass-spring = (1/2) m Dy2(define y from the
      equilibrium position)
      • At the equilibrium position, the object is moving
      quickly, and Dy =0. KE = (1/2) m Dv2

    Conservation of Energy dictates that:
            DPEspring-mass = - DKE
          (1/2)k Dy2 = - (1/2) m Dv2
   Etotal = PEspring-mass + KE = constant
All of the PE goes into KE, and then back again!
   Graphing Energies

What are the x-axis, y axis? Units?
      x axis (independent variable: height)
      y axis (dependent variable: PEgrav)

Which quantity (energy) is the easiest to graph?
  Etot ? PEgrav? What about KE?

   Where should the origin (0) be placed?
   Where does it most make sense?
     Should the floor be 0m?
        Potential Energy and Forces:
           Springs, Gravitational

The indicator is how much the spring is stretched or compressed,
Dx, from its equilibrium position.
                                                     x
              DPEspring = (1/2) kDx2

   The indicator is the change in vertical distance that
    the object moved (I.e. change in the distance between the
    center of the Earth and the object)


                  ∆PEgrav =                     h
PE vs displacement: Force




  [-]   Displacement from equilibrium y [+]
PE vs displacement: Force




                 direction of force




  [-]   Displacement from equilibrium y [+]
PE vs displacement: Force




                      direction of force




  [-]   Displacement from equilibrium y [+]
               PE vs displacement: Force




On this side
force
pushes
down
                                                    Forces from potentials
                                                       point in direction
                 Equilibrium                        that (locally) lowers PE

On this side     [-]   Displacement from equilibrium y [+]
force
pushes up
    Potential Energy vs r and Forces


• Force is always in direction that decreases PE
• Force is related to the slope -- NOT the value of PE
• The steeper the PE vs r graph, the larger the force
What does this to do with real world??
                                            Why does it take more
• Three-phase model of matter               energy to vaporize than
                                                   to melt?
                                                Whst is Ebond?
• Energy-interaction model
                                             r
• Mass-spring oscillator

• Particle model of matter
    Particle model of bond energy
    Particle model of thermal energy
                    We will model real atoms of liquids
                and solids as oscillating masses and springs
•Thermodynamics            Particle Model   of Matter
• Ideal gas model
• Statistical model of thermodynamics
Introduction to the Particle Model
      Potential Energy between two atoms
P
E

    Repulsive:
    Atoms push apart as they
    get too close

                                    Flattening:
                                    atoms have negligible forces
                                    at large separation.

                                  separation

                                                  r



                               Distance between the atoms
         Closed Book




Make sure above boxes are filled!

								
To top