Foucault's Pendulum Experiment

I'm reading an introductory book on astronomy called _Discovering
Astronomy_ by William H. Jeffrys and R. Robert Robbins. On page 7 is
a description of the pendulum experiment by Foucault in 1851 designed
to prove that the earth rotates on its axis. Theoretically, the
pendulum should rotate opposite to the Earth's rotation. Question 9
asks: "Why doesn't the plane of oscillation of the pendulum rotate at
the equator?" I don't know the answer. Can anyone tell me why?

Thanks.

--

Cindy Smith Unless the LORD build the house,
they labor in vain who build.
Unless the LORD guard the city,
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