What is seconds pendulum 

<a data-ved="0ahUKEwiyooLvt7TSAhVCOY8KHUShB-sQ9QEIHTAA" href="https://www.google.co.in/imgres?imgurl=https://upload.wikimedia.org/wikipedia/commons/thumb/f/f2/Pendulum2secondclock.gif/220px-Pendulum2secondclock.gif&imgrefurl=https://en.wikipedia.org/wiki/Seconds_pendulum&h=132&w=220&tbnid=xXcb3Ti7ty5QPM:&vet=1&tbnh=105&tbnw=176&docid=Fiqrpi0P8wtiiM&usg=__FXiyBXQQAmRJ6W4z2VCBZZy1HS4=&sa=X&ved=0ahUKEwiyooLvt7TSAhVCOY8KHUShB-sQ9QEIHTAA" id="xXcb3Ti7ty5QPM:" jsaction="fire.ivg_o" role="link" tabindex="0" tag="bia"></a>

A seconds pendulum is a pendulum whose period is precisely two seconds; one second for a swing in one direction and one second for the return swing, a frequency of 1/2 Hz. A pendulum is a weight suspended from a pivot so that it can swing freely.

When a pendulum is displaced sideways from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position. When released, the restoring force combined with the pendulum's mass causes it to oscillate about the equilibrium position, swinging back and forth. The time for one complete cycle, a left swing and a right swing, is called the period. The period depends on the length of the pendulum, and also to a slight degree on its weight distribution (the moment of inertia about its own center of mass) and the amplitude (width) of the pendulum's swing.