Coin's motion under water Need Explanation

[kushubham9]

Homework Statement

There is time-pass game, "Coin in a Bucket".
In this game, we take a bucket full of water, and in the middle there is a small cup.
We are asked to put the coin in the small cup from above the bucket.

Now the point is, that whenever we place the coin from top of the bucket, it tumbles, rotates and gets displaced from the actual position.
I actually need to know what is responsible for this rotation and random movement of coin under water.?

 

[CWatters]

Edit: My initial post was probably too helpful.

Why do you think it tumbles?