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Announcements 12/3/12

Announcements 12/3/12. Prayer Wednesday: Project Show & Tell Cade & Seth – musical cadences Tess & Brigham - pvc instrument Tyler - sonoluminescence Ryan Peterson - particle collision simulator Konrie, Dallin, Hsin Ping – hot air balloon

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Announcements 12/3/12

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  1. Announcements 12/3/12 • Prayer • Wednesday: Project Show & Tell • Cade & Seth – musical cadences • Tess & Brigham - pvc instrument • Tyler - sonoluminescence • Ryan Peterson - particle collision simulator • Konrie, Dallin, Hsin Ping – hot air balloon You will present in that order; a 9 minute cut-off for each group. • Wednesday: no reading assignment, but there’s still a warmup quiz • Final exam: Mon, Dec 10 – Thurs Dec 13, in Testing Center • Final exam review: vote on times by tonight Frank and Ernest

  2. From warmup Extra time on? Other comments?

  3. HW 37-3: Elastic Collision 1 kg 2 kg 1 kg 2 kg v1,after = ? 9 m/s v2,after = ? 0 m/s 3 m/s 6 m/s ? Check momentum cons: (1)(9) + (2)(0) = -(1)(3) + (2)(6) 9 = 9  5 m/s 2 kg 2 kg 1 kg 1 kg 1 m/s 8 m/s 5 m/s 4 m/s ? Check momentum cons: (1)(4) - (2)(5) = -(1)(8) + (2)(1) -6 = -6 

  4. Elastic Collision 1 kg 2 kg 1 kg 2 kg 0.3 c 0.9 c 0.6 c 0 m/s ? Check: (1)(0.9) + (2)(0) = -(1)(0.3) + (2)(0.6) 0.9 = 0.9  Is momentum conserved??? 0.5 c 2 kg 2 kg 1 kg 1 kg 0.14 c 0.70 c 0.5 c 0.73 c ? Check: (1)(0.73) - (2)(0.5) = -(1)(0.70) + (2)(0.14) -0.27 = -.41 Х

  5. Relativistic Momentum • “The Truth”:

  6. Momentum, Sgmv, is conserved in every reference frame!!! (disclaimer: has to be elastic collision, or else mass not conserved) Elastic Collision 1 kg 2 kg 1 kg 2 kg 0.78 c 0.9 c 0 m/s 0.40 c g = 2.29 g = 1.09 g = 1.60 ? Check: (2.29)(1)(0.9) + 0 = -(1.09)(1)(0.4) + (1.60)(2)(0.78) 2.06 = 2.06  0.5 c 1 kg 2 kg 1 kg 2 kg 0.73 c 0.5 c 0.46 c 0.75 c g = 1.46 g = 1.15 g = 1.51 g = 1.13 ? Check: (1.46)(1)(0.73) – (1.15)(2)(0.5) = -(1.51)(1)(0.75) + (1.13)(2)(0.46) -0.095 = -0.095 

  7. From warmup • What is the maximum momentum that a particle with mass m can have? • There is no maximum momentum!

  8. Momentum vs. Velocity b Why do they agree at small velocities?

  9. From warmup • I often call "E=mc2" the most misquoted equation in history. Why might that be? • Because E does *not* equal mc^2. E = *gamma* times mc^2. See Eqn 39.26 (8th edition). The quantity mc^2 is only the rest energy.

  10. Relativistic Energy • Momentum  Force (F = dp/dt) • Force  Work (W =  Fdx) • Work  Energy (Ebef + W = Eaft) For mass = 1 kg Result: Correct KE KE (joules) ½ mv2 b Why can’t anything go faster than c?

  11. A Word About Units • eV • MeV • MeV/c2

  12. Clicker question: • Hydrogen atoms consist of one electron which is bound to a proton by electromagnetic forces. If I very carefully “weigh” a hydrogen atom, what will I get? • The mass of an electron plus the mass of a proton • Something a little BIGGER than (a) • Something a little SMALLER than (a) • Something entirely different from (a) Ebef + W = Eaft

  13. Clicker question: • A nuclear power plant generates 10 million Watts of power nonstop for a day. How much less do the fuel rods weigh at the end of the day? • around 0.0001 grams • around 0.01 grams • around 1 gram • around 0.1 kg • around 10 kg Nuclear power is not alone in converting mass to energy, ALL power sources do this!

  14. Elastic Collision 1 kg 2 kg 1 kg 2 kg 0.40 c 0.9 c 0 m/s 0.78 c g = 2.2942 How did I find out the two speeds after the collision? Conservation of momentum: Conservation of energy:

  15. Elastic Collision 1 kg 2 kg 1 kg 2 kg 0.40 c 0.9 c 0 m/s 0.78 c g = 2.2942

  16. Relationship between E and p • Classical: KE = ½ mv2 = ? (in terms of p) • Relativistic: E = gmc2 = ? (in terms of p) What if m=0? ? Proof:

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