Question

why pendulum clocks generally go faster in winter and slow in summer​

Answer 1

During summer, length of the pendulum increases due to which the time period T increases and pendulum takes more time to complete one oscillation. Thus it slow in summer. During winter length decreases, decreasing the time period. Consequently pendulum gains time and dock becomes fast.

Answer 2

In summer length of the pendulum is increased as earth goes near the sun...as length increases time period also increases.