Water surface tension
Cups, paper clips, needle and paper towel or napkin.
How to make it:
Take cup of water and carefully place your paper clip or needle with small piece of paper towel under it onto water surface.
What to know:
Due to the surface tension, small objects will "float" on the surface of a fluid, as long as the object cannot break through and separate the top layer of water molecules. When an object is on the surface of the fluid, the surface under tension will behave like an elastic membrane.