When we put a little pin on the surface of water, it floats; is this because of surface tension or buoyancy? Can somebody also draw a force diagram for me to explain how surface tension of water supports an object. And anybody has any advise for me that I can do any simple experiment to demonstrate water-surface tension?
The pin floats on the surface of water because of water's surface tension. When a pin is delicately placed on the surface of still water, it creates a small depression on the water's surface. If the pin is of unit length, then through out its length, the water's surface experiences a force T. If $\alpha$ is the angle of depression, then there is a net upward force $2T\sin\alpha$ that balances the pin's weight. You may refer to the figure for the meaning of symbols.
The blue circle is the transverse section of the pin. That is, the pin is placed perpendicular to the screen.
The force $2T\sin\alpha$ is analogous to the normal reaction of a solid surface.
Surface tension provided by the surface molecules of water and its buoyancy together are responsible for the floating of the pin...they are generally related in such situations. Moreover Surface tensions is a combined factor of buoyancy in certain terms.
Hope that helps you in brief.
When someone floats on water, it’s all done with the help of surface tension and buoyancy. When someone relaxes gently on water, it creates a small depression on the water's surface. Surface tension and buoyancy both work together to keep the person or object a float. Surface tension keeps the person or object from falling into the water; but buoyancy pulls up the person or object. Surface tension is made by the molecules in the water.