# Video: fun physics phenomena

Bookmarked for my kid!

Hmm, 1 and 5 seem obvious to me, and in 3, it seems like water being attracted to an electrically charged cup is just a matter of distance vs attractive force for three effective point sources (so I don’t know why he’s just saying “nope, that’s not it, ha ha!”). 2 and 4, though, completely elude me.

I believe that the cup attracting the water might happen if the cup were charged or not (now i have to try it!). The fast moving air surrounding the water stream creates an area of low pressure into which things are attracted. If you hold a pingpong ball suspended by a string it will be drawn into the water stream and held there by this pressure gradient. Conversely if you are holding the cup so that IT cannot move into the low pressure the water, which is free to move, may be drawn into the lower pressure space. This will only work for small streams because the force on the water due to the pressure gradient will be small compared to the force of gravity on a larger amount of water.

I was shown the last one with amaretti biscuit wrappers - you sometimes get coloured flames, and you don’t waste tea.

Also, I was taught to balance it on your outstretched flat palm not a plate when you do it - there’s a great moment of terror when it really really feels like it’s going to burn you, and then it takes off just in time. Or at least, it always has for me.

Not to worry, it doesn’t look like any actual tea was wasted.

My guesses:

1 - If there’s an imbalance along the stick, the shorter end is lighter and provides less friction.

2 - When holding in portrait mode, any imbalances due to wind resistance are exaggerated as the weight is spread out away from the axis of rotation. Spinning in landscape mode doesn’t have this effect so much as the weight is closer to the axis. When spinning along the thin edge, the rotation is more stable because any imbalances will tend to correct themselves back to the rotation where there is least wind resistance.

3 - Not really sure, but maybe something to do with what @electronmom2000 said. It doesn’t work for me with a glass though, so maybe it is something to do with the static electricity.

4 - Cereal has added iron, which might be enough to be attracted by a magnet if you take out most of the friction.

5 - You have created an updraft of warm air from burning the tube for a few seconds and the last bit is light enough to travel up it.

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