How does the pendulum oscillates in water?

Question

And why does it oscillates like that?? :)

Answer 1

In water, due to buoyancy, the net downward force on the bob will be less and effective g will be less.

=> time period of pendulum will be more meaning it will oscillate slowly.

Answer 2

Yes, as your other respondent mentioned, the weight of the bob would be less, but actually that would have no effect on the period of oscillation, which is only dependent on the length of the pendulum.

What does have an effect is the viscosity of water. In air, very little energy is lost to the medium the pendulum is in; that is, it does not lose much energy to the surrounding air molecules. In water, it would lose a very great deal of energy to the water. In fact, it would lose so much that it would only manage a few swings before all of the kinetic energy of the moving bob would have been absorbed by the water.