Lecture_13_(Student_Handout)

Lecture_13_(Student_Handout) - Phys 172: Modern Mechanics...

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Phys 172: Modern Mechanics Summer 2009 sys sys surr sys net net pFt E W Q L t τ Δ= Δ Δ = + Δ GG Lecture 13 – Energy in Macroscopic Systems Read 6.8 – 6.11
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Open and Closed Systems Today: Energy in Macroscopic Systems Energy In Atomic Bonds Thermal Energy and Specific Heat
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Chemical Bonds in Solids 2 s 1 Perfect spring: U= k s 2 S E U for two neutral atoms Atoms in solids stay close to equilibrium positions (lattice spacing = d). In vicinity of d, atomic potential looks like perfect spring potential!
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Energy in A Solid At Rest 2 solid solid EM c = • binding energy (like K+U inside hydrogen atom) • interaction energy between atoms/molecules • kinetic energy of atoms/molecules (jiggling) chemical energy thermal energy 2 , , 1 2 ij i i i i particles mc UK = =+ +
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Macroscopic Systems & Thermal Energy Even if a block of metal is at rest, the individual atoms have K (they’re jiggling) and the bonds have U spring . jiggling spring atoms bonds thermal energy KU ⎛⎞ += ⎜⎟ ⎝⎠ ∑∑ Keeping track of 10 23 atoms (K) and 10 46 bonds (U s ) isn’t so easy. Lump it all together:
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CLICKER QUESTION #1 Two lead bricks moving in the +x and x directions, each with kinetic energy K , smash into each other and come to a stop.
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This note was uploaded on 09/14/2009 for the course ENGR 126 taught by Professor Oakes during the Fall '08 term at Purdue University-West Lafayette.

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Lecture_13_(Student_Handout) - Phys 172: Modern Mechanics...

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