[kakak91]

I have to find out about the pendulum movement in water, air and vacuum...

Hope that anyone can give me the information as soon as possible...

I have to submit my project work next week>>>

THANK YOU.:)

[Capuchin]

The only difference is the damping effect.

In a vacuum, there is no damping, because a perfect vacuum has no viscosity.
In air, there is slight damping, as you have probably seen in your experiments. If you leave the pendulum swinging it will gradually lose amplitude over many periods until it comes to a stop (after hundreds or more periods).
Water is much more viscous than air, so the damping is much more pronounced. I'm not actually sure how much the damping would be, but I would hazard a guess that it would be something approaching critical damping (you should know what this means). It might come to a stop over tens or fewer periods.
If you went to something even more viscous, like vegetable oil, the damping would be critical.

Now that describes the amplitude - how do you think the period of the pendulum might change?