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Quiz information on the course website Include : Quiz answers (posted by ~5pm Tuesdays)

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

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Quiz information on the course website Include : Quiz answers (posted by ~5pm Tuesdays)

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  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)

  2. 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.

  3. Quiz 3 8:30-8:50am TODAYHave your calculator readyClosed book Next lecture February 5Quiz 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.

  4. Energy systems so far KE Speed Emass-spring Distance from the equilibrium position Ethermal T Ebond Phase Eelectric PEgrav height Enuclear 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.

  5. Conservation of Energy Etot = 10 Joule 5 3 2 Nature happens…

  6. Energy Interaction Model Etot = 10 Joule 7 2 1

  7. Energy Interaction Model Etot = 10 Joule 7 2 1 (-3J) + (+5J) + (-2J) = 0 ∆Eorange + ∆ Emelon + ∆ Egrape = 0 Etotal =Eorange + Emelon + Egrape

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

  9. 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

  10. 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

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

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

  13. Bowling Ball a c b When is the speed of the bowling ball maximum? Starting point (b) When rope is vertical (c) At point c.

  14. a c b When is the speed of the bowling ball maximum? Bowling Ball (b) When rope is vertical

  15. a c b When is the PEgravity of the bowling ball maximum? Bowling Ball Starting point When rope is vertical At point c

  16. a c b When is the PEgravity of the bowling ball maximum? Bowling Ball Starting point (c) At point c.

  17. Consider a simple pendulum: Conservation of Energy 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 v2 Conservation of Energy dictates that: PEgravity = - KE mgh = - (1/2) m v2 Etotal = PEgrav + KE = constant All of the PE goes into KE, and then back again!

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

  19. Bowling Ball Final Initial (In motion) KE Speed PEgrav Height

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

  21. 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, x, from its equilibrium position. • k is a measure of the “stiffness” • of the spring, with units [k] = kg/s2. • x: Much easier to stretch a spring a little bit than a lot! PEspring = (1/2) kx2 x

  22. Mass-Spring Systems PEmass- spring = (1/2) ky2+C • k is a property of the spring only • PEmass-spring does not depend on mass • PE = 0 arbitrary

  23. Mass-Spring Systems KE Speed PEmass-spring ∆y

  24. Mass-Spring Systems KE Speed PEmass-spring ∆y

  25. Conservation of Energy • Just like a simple pendulum: • At the peak of the amplitude, the object is at rest. PEmass-spring = (1/2) m y2(define y from the equilibrium position) • At the equilibrium position, the object is moving quickly, and y=0. KE = (1/2) m v2 Conservation of Energy dictates that: PEspring-mass = - KE (1/2)k y2 = - (1/2) m v2 Etotal = PEspring-mass + KE = constant All of the PE goes into KE, and then back again!

  26. 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?

  27. ∆PEgrav = x Potential Energy and Forces: Springs, Gravitational • The indicator is how much the spring is stretched or compressed, x, from its equilibrium position. PEspring = (1/2) kx2 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) h

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

  29. PE vs displacement: Force direction of force [-] Displacement from equilibrium y [+]

  30. PE vs displacement: Force direction of force [-] Displacement from equilibrium y [+]

  31. PE vs displacement: Force On this side force pushes down Forces from potentials point in direction that (locally) lowers PE Equilibrium On this side force pushes up [-] Displacement from equilibrium y [+]

  32. 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

  33. r What does this to do with real world?? Why does it take more energy to vaporize than to melt? Whst is Ebond? • Three-phase model of matter • Energy-interaction model • Mass-spring oscillator • Particle model of matter • Particle model of bond energy • Particle model of thermal energy • Thermodynamics • Ideal gas model • Statistical model of thermodynamics We will model real atoms of liquids and solids as oscillating masses and springs Particle Model of Matter

  34. r Introduction to the Particle Model Potential Energy between two atoms PE Repulsive: Atoms push apart as they get too close Flattening: atoms have negligible forcesat large separation. separation Distance between the atoms

  35. Closed Book Make sure above boxes are filled!

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