Flip Flop Flower (spelled “Flip Flap” on the side!)
Flip flop flower
This is another interesting item that can be bought for about $5 from "$2" type shops or from some gift shops.
When placed in sunlight the central flower head starts to nod rhythmically as the two leaves flip and flop in unison about a central pivot.

I was keen to see what kind of arrangement is used inside to produce the motion. Obviously the photocell on the top shows that there is an electrical basis to the mechanical action. But is there a motor inside? Or is there some other electro-mechanical method used?

Inside the flip flop flower
The flowerpot part can be opened by unscrewing the two deeply seated screws underneath. I was surprised by the mechanism and the clear use of physics principles in generating the motion.

The labeled photo shows that, while the flip flop flower does not use a normal motor, nevertheless the “motor effect” is at the heart of the mechanism.  

The photocell generates around one volt and charges a 220 microfarad capacitor that is connected in parallel with an integrated circuit (IC). The IC’s function is to discharge the capacitor periodically through a coil of fine copper wire. When this happens the magnetic field produced around the coil ‘kicks’ the strong neodymium magnet nearby. The magnet is attached to one of the green leaves which then swings as a result of the kick. The other leaf is mechanically linked to the first one so that it swings in unison.

Detail of flip flop flower mechanism
The flower head is positioned in the centre of the leaf mechanism and acts as a forced pendulum. It is weighted at the bottom by ceramic magnets which themselves are kicked periodically by a neodymium magnet/ceramic magnet combination as they swing. Making the flower head magnetically linked removes the need for further mechanical linkage which would introduce more friction and make the whole apparatus harder to get going and keep going.

Finally, the timing programmed into the IC seems to match the natural period of the leaf mechanism’s swing producing resonance. This means that even under low light the tiny kicks from a weak current through the coil will combine constructively to produce some motion in the flip flop flower.

Here is a link to a YouTube video clip that shows a similar version in motion: Solar Flip Flap Flower - inside

Please feel free to email me if you have any questions or to suggest improvements in this resource.
Cheers, Denis