Surface tension is a property of a liquid that allows it to resist an external force. It is caused by the cohesive forces between molecules in the liquid, which tend to draw the molecules together and make the surface of the liquid behave as if it were a stretched membrane or elastic skin.
Examples of surface tension include:
The ability of a liquid to form a droplet or a bead when it is placed on a surface. The surface tension of the liquid helps to hold the droplet together and prevent it from spreading out.
The ability of a liquid to flow through a small hole or capillary tube. The surface tension of the liquid helps to pull it through the small opening.
The ability of insects such as water striders to walk on water. The surface tension of the water helps to support their weight.
The ability of soap bubbles to hold their shape. The surface tension of the soap solution helps to keep the bubble walls stretched and maintain the bubble's round shape.
The ability of mercury in a thermometer to form a thin, stable column. The surface tension of the mercury helps to keep it together and prevent it from spreading out.