Physics 121 11/01/10 Prof. E. F. Redish 1 11/01/10 1 Physics 121 *playing the original cover by Tom Rush 11/01/10 2 Physics 121 11/01/10 3 Physics 121Physics 121 11/01/10 Prof. E. F. Redish 2 11/01/10 Physics 121 4 11/01/10 8 Physics 121 t 1 t 2 t 3 t 4 t 5 t 6 R Period = time to go around once T = 4 (t3 – t1) (Why?) Speed = 2R / T (Why?) t 7 t 8 11/01/10 9 Physics 121 trv=t 1 t 2 1r2rr12rrr=dtrdv=Physics 121 11/01/10 Prof. E. F. Redish 3 11/01/10 10 Physics 121 t 1 t 2 1v2vv12vvv=tva=dtvda=11/01/10 11 Physics 121 t 1 t 2 R 1r1r2r2r2v2v1v1vvr11/01/10 12 Physics 121 R R v t v v a t Similar triangles imply RvaRvvavtaRtv2===Physics 121 11/01/10 Prof. E. F. Redish 4 11/01/10 13 Physics 121 rRvarRrrRvaˆectorposition v ofdirection in r unit vecto ˆectorposition v center in to pointing 22=====11/01/10 14 Physics 121 11/01/10 15 Physics 121 rRmvFrRvmFrRvamFanetnetnetˆˆ ˆ 222====always in order for the object to move in a circle with constant speed. Therefore, to do this, we need a net force. A(n inward) radial net force is needed to maintain circular
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