Surface Tension
Surface Tension is the thin, stretchy skin that forms on top of water because water pulls itself together.
Water has a thin, stretchy layer on its surface, like plastic wrap stretched across a bowl. Small, light things like a paper clip can rest on top without sinking. The water at the top pulls toward itself, forming a skin that holds the weight. Push through that skin, and the object drops to the bottom.
Explaining surface tension by grade level
Water has a thin skin on top. That skin is strong enough to hold up small things. When you add soap to water, it breaks that skin. That is why soap bubbles pop when the skin gets too weak.
Projects that explore surface tension
Water molecules cling tightly together — that pull is surface tension, the force that holds a water surface together. It keeps oil floating in a separate layer, no matter how long you stir. When you add liquid soap, it breaks that hold and lets the oil blend into the water.
Milk has surface tension just like water — a thin skin on top that holds everything in place, including drops of food coloring. When you touch dish soap to the milk, it breaks that surface tension. As a result, the colors spin and race away from the soap, swirling toward the edges in seconds.