Centripetal force
\[
F_c = ma_c = {{mV^2}\over r}=m\omega^2 r, \qquad \vec{F_c}\> \|\> \vec{a_c}\> \bot\> \vec{V}
\]
$F_c$ can be provided by:
-
model airplane: $F_c=T$, tension in the wire
-
satellite in orbit: $F_c=G{{mM_E}\over{R^2}}$, Earth's gravity
-
car turning: $F_c=f_s$, static friction (between the tire and the road)
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