Why do spinning fidget spinners skip on water? I saw a recent video on a fidget spinner skipping at water after its angular velocity was raised to a high rate. I know spin has something to do with stabilizing the spinner, but what exactly does the spin have to do with skipping the fidget spinner on water and why does it not work at low speeds?
 A: If you get the angle right, say you throw the spinner at less than 20 degrees to the water, it should skip, 
Conservation of momentum says that as the stone drops into the water and forces some of it downwards, the stone is forced vertically upwards.   So it should skip if you bend down along the edge of the water to throw it.
Skipping Stones

Each time the stone skips the surface of the water it is reflected upwards, its downward velocity is reversed, and its horizontal velocity is reduced. Since the trailing edge of the stone typically breaches the water first, it is also pitched down slightly.  This brief downward pitching affects the direction of the stone’s path.  Each subsequent bounce slows it down until it penetrates the water surface rather than skipping over it.  The height from which it is thrown, the angle, the impact attitude, and the condition of the water’s surface - all are additional factors that affect how many skips occur and how quickly the stone splashes down.

So why do we need to spin it as well?
If after it bounces,  the stone is spinning, it is more likely to stay roughly parallel to the surface, (so it is set up the way you threw it originally) so more chance of more bounces.  Spin motion induces a stabilizing torque that can maintain the angle (less the 20 degrees) that you first threw it at.  This is the point of spining it as fast as you can, you get more skips.
