Lecture04

Lecture04 - Physics 7A-2 (C/D) Professor Chertok Fall, 2008...

Info iconThis preview shows pages 1–22. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Physics 7A-2 (C/D) Professor Chertok Fall, 2008 Lecture 4 Original presentations copyright M. Chertok 2008. All rights reserved. Questions? Outline for today Conservation of Energy: T or F? Recap of DLM 5-6 Ch. 3 -- the particle model Quiz 4 M. Chertok, Physics 7A 3 Which of the following can be valid? Use your clickers By the way... if you Which of the join the session before following c(forbe valid? an the 9am I restart it lecture) this might make your clickers not Use your clickers function properly Which of the following can be valid? Use your clickers Eth + Eb = Q M. Chertok, Physics 7A 5 Eth + Eb = W M. Chertok, Physics 7A 6 ΔEth + Eb = Q M. Chertok, Physics 7A 7 ΔEth + ΔEb = W M. Chertok, Physics 7A 8 ΔKE + ΔPE = W M. Chertok, Physics 7A 9 ΔKE + ΔPE = 0 M. Chertok, Physics 7A 10 ΔKE = W M. Chertok, Physics 7A 11 Eth + Eb = W M. Chertok, Physics 7A 12 KE = W M. Chertok, Physics 7A 13 ΔKE + ΔPE = Q+W M. Chertok, Physics 7A 14 ΔKE + ΔPE = Q-W M. Chertok, Physics 7A 15 Recap of DLM 5 & 6 DLM 5 2.1.3 - FNTs from DLM 4 Rocks thrown in different directions cars launched from springs bucket of water on rope 2.1.4 - Another new energy system Rotational KE 2.2.1 - Modeling with quantitative expressions... linear vs. quadratic indicators modeling a thrown ball M. Chertok, Physics 7A 17 DLM 6 2.2.2 - Followup of FNTs from DLM 5 Modeling thrown ball - entire process vs. two subprocesses. Is the result the same? Show that for ball thrown upward, speed at some height going up = speed at same height going down Redefine y=0 as hand, not floor. Any change in result? Water balloon dropped from building. Thermal energy plus mechanical energy Mass-spring: find work, find speeds at various points M. Chertok, Physics 7A 18 DLM 6, (ii) 2.3.1 - Graphically representing energy relationships PE+KE=Etot is equivalent to ΔKE + ΔPE = 0 Falling ball: Graph PE, Etot, KE for different choices of y=0. What changes and what remains same? Why plot PE and Etot first? Mass-spring: Can we set y=0 wherever we want? No! M. Chertok, Physics 7A 19 Changing (location of) y=0 y=5 y=2 y=0 By changing y=0, we change the PEg as well as Etot So, graphs of these will look different But: maximum height above floor unchanged! M. Chertok, Physics 7A 20 Changing (location of) y=0 y=5 y=2 y=0 y=0 By changing y=0, we change the PEg as well as Etot So, graphs of these will look different But: maximum height above floor unchanged! M. Chertok, Physics 7A 20 Changing (location of) y=0 y=5 y=3 y=2 y=0 y=0 By changing y=0, we change the PEg as well as Etot So, graphs of these will look different But: maximum height above floor unchanged! M. Chertok, Physics 7A 20 Changing (location of) y=0 y=5 y=3 y=2 y=0 y=0 y=-2 By changing y=0, we change the PEg as well as Etot So, graphs of these will look different But: maximum height above floor unchanged! M. Chertok, Physics 7A 20 Changing (location of) y=0 y=5 y=3 y=2 y=0 } what is Etot here? y=0 y=-2 By changing y=0, we change the PEg as well as Etot So, graphs of these will look different But: maximum height above floor unchanged! M. Chertok, Physics 7A 20 DLM 6, (iii) 2.2.3 - Checking understanding with a new phenomenon Vertical pulley with string and two unlike hanging masses Which will accelerate faster? M=220 g, m=200 g or M=70 g, m=50 g M. Chertok, Physics 7A 21 Don’t call it “Atwood’s Machine”! Q: which set of masses will win? Hint initial state: just as you release masses final state: masses have moved distance d and have speed v How many bubbles in the E.I.D.? Closed or open system? M m M. Chertok, Physics 7A 22 Chapter 3 Particle model of matter Main idea of chapter: investigate “magic” spring Try to apply as basis for bond energy Remember connection between force and PE Which was...? M. Chertok, Physics 7A 24 Force: gravity Potential Energy ( J ) PE height above ground (m) What is the strength and direction of force of gravity? M. Chertok, Physics 7A 25 Force: gravity Potential Energy ( J ) PE height above ground (m) What is the strength and direction of force of gravity? M. Chertok, Physics 7A 25 Force: gravity Potential Energy ( J ) PE height above ground (m) What is the strength and direction of force of gravity? M. Chertok, Physics 7A 25 Force: gravity Potential Energy ( J ) PE height above ground (m) What is the strength and direction of force of gravity? M. Chertok, Physics 7A 25 Force: gravity Potential Energy ( J ) PE height above ground (m) What is the strength and direction of force of gravity? Strength: constant. Direction: toward Earth M. Chertok, Physics 7A 25 Force: regular spring Energy PE -y displacement from equilibrium +y M. Chertok, Physics 7A 26 Force: regular spring Energy PE -y displacement from equilibrium +y Where is force greatest? M. Chertok, Physics 7A 26 Force: regular spring Energy PE -y displacement from equilibrium +y Where is force greatest? Where is force weakest? M. Chertok, Physics 7A 26 Force: regular spring Energy PE -y displacement from equilibrium +y Where is force greatest? Where is force weakest? What is the direction of the force? M. Chertok, Physics 7A 26 Force: regular spring Energy PE -y displacement from equilibrium +y Where is force greatest? Where is force weakest? What is the direction of the force? Force is negative of derivative of PE graph! M. Chertok, Physics 7A 26 Force: regular spring Energy PE -y displacement from equilibrium +y Where is force greatest? Where is force weakest? What is the direction of the force? Force is negative of derivative of PE graph! (Force is in direction that tries to lower the PE) M. Chertok, Physics 7A 26 Force: regular spring Energy PE -y displacement from equilibrium +y Where is force greatest? Where is force weakest? What is the direction of the force? Force is negative of derivative of PE graph! (Force is in direction that tries to lower the PE) M. Chertok, Physics 7A 26 Force: regular spring Energy PE -y displacement from equilibrium +y Where is force greatest? Where is force weakest? What is the direction of the force? Force is negative of derivative of PE graph! (Force is in direction that tries to lower the PE) M. Chertok, Physics 7A 26 Force: regular spring Energy PE -y displacement from equilibrium +y Where is force greatest? Where is force weakest? What is the direction of the force? Force is negative of derivative of PE graph! (Force is in direction that tries to lower the PE) M. Chertok, Physics 7A 26 Force: regular spring Energy PE -y displacement from equilibrium +y Where is force greatest? Where is force weakest? What is the direction of the force? Force is negative of derivative of PE graph! (Force is in direction that tries to lower the PE) M. Chertok, Physics 7A 26 Force: regular spring Energy PE F=0 -y displacement from equilibrium +y Where is force greatest? Where is force weakest? What is the direction of the force? Force is negative of derivative of PE graph! (Force is in direction that tries to lower the PE) M. Chertok, Physics 7A 26 Graphs of Two-Object system Energy -y displacement from equilibrium +y ??? separation, r (m) M. Chertok, Physics 7A Energy 27 Graphs of Two-Object system Energy -y displacement from equilibrium +y ??? separation, r (m) M. Chertok, Physics 7A Energy 27 Graphs of Two-Object system Energy 0 separation, r (m) That’s better! Can’t have negative separation M. Chertok, Physics 7A 28 DLM 7 - Starts Today 2.3.2 FNTs from DLM 6: Ball thrown straight up, mass-spring, horizontal mass-spring with friction, skier, masses on pulley 2.4.1 Connection between Force and PE Graphing PE versus distance for PEgrav, massspring |F| = |d(PE)/dr| (“r” is direction coordinate) 2.4.2 Two objects connected by a spring M. Chertok, Physics 7A 29 Two-object system r M. Chertok, Physics 7A 30 Two-object system r r: distance between objects M. Chertok, Physics 7A 30 Two-object system r r: distance between objects r0: distance between objects when spring relaxed (equilibrium position) M. Chertok, Physics 7A 30 Two-object system r r: distance between objects r0: distance between objects when spring relaxed (equilibrium position) We will study this in great detail M. Chertok, Physics 7A 30 Atomic hypothesis ... I believe it is the atomic hypothesis... that all things are made of atoms-little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another... M. Chertok, Physics 7A 31 PE for 2-atom system e en ship Potential Energy (in units of well depth, ") Pair-wise or Atom-Atom Potential (as modeled with the Lennard-Jones Potential) 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 Pair-wise Potential (as modeled with the Lennard-Jones Potential) hat . tion um rticle -1.2 distance between centers of atoms, r (in units of particle diameter, ! ) M. Chertok, Physics 7A 32 PE for 2-atom system e en ship Potential Energy (in units of well depth, ") Pair-wise or Atom-Atom Potential (as modeled with the Lennard-Jones Potential) 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 Pair-wise Potential (as modeled with the Lennard-Jones Potential) a/k/a Lennard-Jones Potential hat . tion um rticle -1.2 distance between centers of atoms, r (in units of particle diameter, ! ) M. Chertok, Physics 7A 32 PE for 2-atom system e en ship Potential Energy (in units of well depth, ") Pair-wise or Atom-Atom Potential (as modeled with the Lennard-Jones Potential) 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 Pair-wise Potential (as modeled with the Lennard-Jones Potential) a/k/a Lennard-Jones Potential hat . tion um Think about -1.2 rticle strength and direction of force distance between centers of atoms, r (in units of particle diameter, ! ) M. Chertok, Physics 7A 32 PE for 2-atom system e en ship Potential Energy (in units of well depth, ") Pair-wise or Atom-Atom Potential (as modeled with the Lennard-Jones Potential) 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 Pair-wise Potential (as modeled with the Lennard-Jones Potential) a/k/a Lennard-Jones Potential Note location of 2.6 2.8 x-axis 3 hat . tion um Think about -1.2 rticle strength and direction of force distance between centers of atoms, r (in units of particle diameter, ! ) M. Chertok, Physics 7A 32 PE for 2-atom system e en ship Potential Energy (in units of well depth, ") Pair-wise or Atom-Atom Potential (as modeled with the Lennard-Jones Potential) 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 Pair-wise Potential (as modeled with the Lennard-Jones Potential) a/k/a Lennard-Jones Potential Note location of 2.6 2.8 x-axis 3 hat . tion um Think about -1.2 rticle strength and direction of force Note location of PE minimum distance between centers of atoms, r (in units of particle diameter, ! ) M. Chertok, Physics 7A 32 Particle Model of Matter Feynman’s quote |F| = |slope of PE(r)| Direction is such that it reduces the PE Pair-wise PE: general form shown on graph Strong repulsion when too close Attractive when separation greater than equilibrium Attractive force is short range. Attraction becomes weaker as particles separate further M. Chertok, Physics 7A 33 Particle Model, (ii) For system of many particles, phase (s,l,g) depends on Etot High energy: particles unbound -- gas Average separation is much greater than r0 Low energy: particles bound -- solid or liquid Average separation ~ r0 M. Chertok, Physics 7A 34 Particle Model, (iii) Graph is 1-D. However, every particle interacts with all its nearby neighbors. Result is 3-D PE for a given particle. Its minimum defines equilibrium position of particle in solid or liquid. “single particle PE” Each particle in solid or liquid oscillates in 3-D about this equilibrium position M. Chertok, Physics 7A 35 DLM 8 next week 2.4.3 Follow up from DLM 7 -- FNTs This is fair game for the next quiz FNTs are: PEgrav: Earth versus Moon Graph of Two-mass system if k, r0 change Graph of PEelectrical Detailed graph of Lennard-Jones potential Atomic spacing for solids, liquids and gasses M. Chertok, Physics 7A 36 DLM 8 3.1.1 Particle model: Feynman’s quote 3.1.2 PE graph: how particles interact. Force, PE versus separation 3.1.3 Particle separation for solids, liquids and gasses Water Liquid/gaseous nitrogen! M. Chertok, Physics 7A 37 Quiz 4 Quiz 4 Next Friday! Covers: DLM 1 through... DLM 7 (including FNTs discussed in DLM08) M. Chertok, Physics 7A 39 ...
View Full Document

Page1 / 67

Lecture04 - Physics 7A-2 (C/D) Professor Chertok Fall, 2008...

This preview shows document pages 1 - 22. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online