Obodna hitrost
Obódna hitróst (tudi krožílna hitróst , hitrost kroženja) je hitrost , ki jo ima točkasto telo pri kroženju . Obodna hitrost v ima smer tangente na krožnico in je enaka odvodu poti s po času:
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{\displaystyle v={\frac {\mathrm {d} s}{\mathrm {d} t}\!\,.}
Pot s pri kroženju povezuje s kotom zasuka konstantni faktor r — polmer krožnice , po kateri kroži telo. Zato tudi obodno in kotno hitrost povezuje zveza:
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{\displaystyle v=r\omega \!\,,}
oziroma vektorsko :
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{\displaystyle {\vec {\mathbf {v} }={\vec {\boldsymbol {\omega }\times {\vec {\mathbf {r} }=-({\vec {\mathbf {r} }\times {\vec {\boldsymbol {\omega })\!\,.}
Potek izpeljave:
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{\displaystyle v={\frac {\mathrm {d} s}{\mathrm {d} t}={\frac {\mathrm {d} (\theta \cdot r)}{\mathrm {d} t}={\frac {\mathrm {d} (\omega \cdot t\cdot r)}{\mathrm {d} t}=\omega \cdot r\!\ }
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