4. There is a simple pendulum, which has a period of $T=1$ second in summer. In winter, the pendulum length shortens by 0.01 cm. In winter, this pendulum is approximately faster by $\qquad$ seconds in 24 hours (rounded to 1 second).

Note: The formula for the period of a simple pendulum is $T=2 \pi \sqrt{\frac{l}{g}}$, where the period $T$ is in seconds, the pendulum length $l$ is in centimeters, and the gravitational acceleration $g=980$ cm/s${}^2$.
4. 17.

Substituting $T=1$ second into the formula, we get
the summer pendulum length $l=\left(\frac{T}{2 \pi}\right)^{2} g \approx 24.824$ cm, and the winter pendulum length $l^{\prime}=l-0.01 \approx 24.814$ cm. The period of the winter pendulum $T^{\prime}=2 \pi \sqrt{\frac{l^{\prime}}{g}} \approx 0.9998$ seconds. Therefore, in 24 hours, the winter pendulum is faster than the summer pendulum by approximately $24 \times 60 \times 60\left(T-T^{\prime \prime}\right)=17$ seconds.