Homopolar motor
If the wire is electrified, it will produce magnetic field.
This magnetic filed can attract a magnet. So we can make the magnet spin.
This is the principle of a simple motor which called Homopolar motor.
Non-Newtonian fluid
The Non-Newtonian fluid is different form other liquid.
If you punch it, you will be blocked; if you move lightly in the liquid,our hands will feel no resisting force.
This magic effect is from amylopectin,having branch-like molecular structure.
If you punch it hard, the bracnch will be concentrate, blocking you.
Otherwise, it won't concentrate ,and you can move smoothly within the lquid.
Air Cannon
This is formaly called "vortex generator".
Its structure is pretty simple.
It is a barrel with a hole on the bottom and a flexible cover on the top of it.
You can pat the cover slight ly, then fast air flow will be generated form the hole. By Bernoulli Theorem, the air flow will cause an "air ring" on its side, flying for quite a distance.