Lecture7 - Physics 7A – Lecture 7 Winter 2010 Prof. Robin...

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Unformatted text preview: Physics 7A – Lecture 7 Winter 2010 Prof. Robin D. Erbacher 343 Phy/Geo Bldg [email protected] • No Quiz today, Quiz 5 is next week. • Join this Class Session with your PRS clicker! • Check Physics 7 website frequently for updates. • Turn off cell phones during lecture. Review Multiple- Atom Systems: Particle Model of E bond , Particle Model of E thermal Example: H 2 O What is E bond in terms of KE and PE of individual atom (atom pair)? What is E thermal in terms of KE and PE of individual atom (atom pair)? Magnitude of E for a substance is the amount of energy required to break apart “all” the bonds Separation (10-10 m) E bond ≈ -40 x 10-21 Joules Energy required to break a single pair of atoms apart: +8x10-21 J =5 bonds. ⇒ A B KE A pair of atoms are interacting via a atom-atom potential. Only these two atoms are around. In two different situations, the pair have a different amount of total energy . In which situation is E thermal greater? E b) Situation B has a greater E thermal KE Initial Final Okay. Now let us look at the same problem from the perspective of the KE and PE of individual atoms . Which situation is correct in going from initial to final states? Initial Final Okay. Now let us look at the same problem from the perspective of the KE and PE of individual atoms . Which situation is correct in going from initial to final states? • The energy associated with the random motion of particles is split between PE and KE . PE avg = KE avg = E tot /2 Energ y position E tot PE KE thermal not E . Equipartition of Energy • If the atoms in the molecule do not move too far, the forces between them can be modeled as if there were springs between the atoms. • Each particle in a solid or liquid oscillates in 3 dimensions about its equilibrium positions as determined by its single-particle potential. • Another way of stating: Each particle has six “ways” to store the energy associated with its random thermal motion. • We call this “way” for a system to have thermal energy a “ mode ”. Gas Liquids and Solids Modes : Ways each particle has of storing energy....
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This note was uploaded on 08/21/2011 for the course PHYS 7A taught by Professor Erbacher during the Winter '10 term at UC Davis.

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Lecture7 - Physics 7A – Lecture 7 Winter 2010 Prof. Robin...

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