Why can you walk on water?

Water mixed with granular starch is shear thickening, it appears thicker the faster you stirr it. Click on the image on the right for a YouTube film displaying the phenomenon.

This is how it works:

Granular starch, for example potato flour, consists of small particles, like very small rubber balls. There are so many of them that they all the time collide. When you run on the surface they collide so fast that they always touch another particle. They seem to be stuck to each other and the surface apperas solid.



 

When you stand still you will slowly sink. The starch particles collide less frequently and have time to move before hitting another particle. The mixture appears fluid.

 


Click here for a film demonstrating how you can walk on a starch dispersion.

 

Hints on how to do it yourself