3lecture2a08

3lecture2a08 - Physics 2A Lecture 3: Jan 11, 2007 Vivek...

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Physics 2A Lecture 3: Jan 11, 2007 Vivek Sharma UCSD Physics
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Announcements • Resistar’s office is still working on Monday’s PB schedule. Pl. check class website on Monday for news. • 2C section DI Friday, 14:00 in CNTR 119 • When emailing phys2a@physics.ucsd.edu . –please be sure to put in your Section # & your course code # in the subject line • Yes, you absolutely need 2 nd edition of the textbook
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Multiplying Vectors • In mechanics, can express many physical relationships by using vector product • Vector product is not like multiplying #s • Two different kind of vector products –scalar product yields a value that’s scalar –vector product yields another vector !
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Scalar Product Of A & B G Definition : A B ABcos | A || B| cos = φ= φ G G G G i Bco = ( s )A φ Aco = ( s )B φ A B magnitude of B x proj of A on A B magnitude of A x proj of B on B A = = G G i G G i Zero when Largest wh A B ˆˆ ˆ en A || B ˆ ; ; G G i G i i G i ii= ij = j 1= j j i=0
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Scalar Product Of A & B G xx yy zz AB A B A B A B ⋅= + + G G
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Finding Angle Between Two Vectors ˆˆ What 's angle between them? φ G G A=2i+3j+k ; B=-4i+2j-k, x xx yy zz xy yz z 1o AB ABcos AB A Dot prod uct Formula -3 cos = 0.175 14 21 cos ( 0.175) 10 : B 0 ++ ⇒φ = = =− ⇒φ= = G G i
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Vector Product Of A & B: Definition G A B Vector to plane containing A & B with magnitude C | ABsin C| ×= = G G G G G G Right Hand Rule Always two directions perpendicular to a plane, which one to choose ? Follow right hand rule Æ direction of thumb or advance of a right hand screw when vector A sweeps towards vector B Need to practice this until obvious !
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Vector Product Of A & B G As a Result of the Definiti A B - o (B ) C A n ×= = × GG G
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Vector Product Of A & B: Definition G A B Vector
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3lecture2a08 - Physics 2A Lecture 3: Jan 11, 2007 Vivek...

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