CBSE Class 9 Answered

When you draw the pendulum bob to one side, you are displacing it from it's equilibrium position.

Since there is effective vertical displacement. The bob gains PE. As we release the PE is expended to reach towards equilibrium position. So KE increases at the expense of PE. And once at equilibrium position, the KE is maximum.

The KE is now expended to go over the other side. And it again gains the PE. Now KE is completely converted into PE.

And energy interplay cycle repeats itself ideally, but since air molecules present a problem. Each time the bob swings the air molecules are hit. They gain some KE and hence the KE of bob not only is used to increase the PE of bob but towards the air molecules increased KE also.

This we know as friction.

So eventually as we see the energy is converted into PE to KE and back again. But some KE is also dissipated due to friction. But energy is conserved.

Regards,

Team,

TopperLearning.