ADVICE OF THE DAY
The sinking starts when the water starts to flow into the glass. The water level for this part of the experiment should be measured in reference to the water level at the beginning of the sinking.
Answer D) (coin begins to rotate) means a rotation comparable to the rotor of a helicopter.
Please make sure that the cloth is soaking wet.
The "10 cm coin" is the one that is 10 cm away from the pivot point, i.e. the pen, the "20 cm coin" is 20 cm away from the pen. It does not matter which number is printed on the rule at the respective position.
Please take a close look at the film and place the object at a sufficient distance from the glass so that you can see the whole object. If you look from diagonally below, the object you are looking at should be further down at the height of the glass foot. We still had to move our heads a little to see the object piece by piece.