The surface tension of water is enough to hold up light objects like a paper clip (use the smaller size). Fill a glass of water almost to the top. Place a paper clip on top of the water surface. If you have difficulty in making the paper clip float, then place the paper clip on a small (slightly bigger than the paper clip) piece of paper towel (like Bounty paper towel). Place the paper towel with the paper clip on the water surface. When the paper towel becomes fully wet, it will sink, leaving the paper clip on top. Add a drop of liquid soap or detergent close to the paper clip. The paper clip will drop like a brick. The reduced surface tension is no longer sufficient to hold up the denser metallic clip.