How does surface tension support objects if the force is only acting within the liquid?

Question

When a needle is placed on the surface of water what force is balancing the needle ? Surface tension is acting within the liquid, but how is this force acting on needle to keep it balanced?

Answer 1

There are electrostatic forces repelling the atoms of the liquid and the atoms of the needle as they get closer together. The surface tension forces just keep the atoms of the liquid together enough such that the needle can't simply fall through.

You can think of the surface tension like the surface of a trampoline. As the needle moves downward, the electrostatic forces partially hold it up, so it and the surface of the liquid sinks. This starts to build up the stress we call surface tension, just like the elastic forces that get built up in the springs of the trampoline. Eventually they pull hard enough to actually stop the needle's downward movement, and that's where the needle finally rests.