Surface tension is one of water's most important properties. It is the reason that water collects in drops, but it is also why water can travel up a plant stem, or get to your cells through the smallest blood vessels. You can experiment with surface tension using just a few household items.
Surface tension creates the 'skin' on top of the water, but it is also what causes water to stick together in drops. Observe how these drops stick together by experimenting with water and a penny. All you need is a cup of water, a penny, and a medicine dropper. First make a prediction: how many drops of water do you think you can fit on the top surface of the penny? Add one drop. After seeing how much room it takes, do you want to rethink your first prediction? Now continue carefully adding drops until the water spills off the penny. Try this three times, recording the number of drops each time, and then find the average number of drops that can fit. Surface tension is the reason you can fit so much water on the penny. The water molecules attract each other, pulling together so the water doesn't spill. Try this experiment with different-sized coins. Predict how many drops you can fit on a quarter compared with the penny.
For one final surface tension experiment, start with a full glass of water. Predict how many pennies you can add to the water without the glass overflowing. Gently add pennies one by one. Because of surface tension, the water will rise above the rim of the glass before it spills! Compare your original prediction with the number of pennies you were able to add.
Have you ever wondered why rivers and lakes freeze in the winter, but oceans do not? In this experiment we will see that it is the presence of salt in the ocean that makes it less likely to freeze.
How did the water freeze when surrounded only by saltwater? The salt broke apart the bonds between the water molecules in the ice, causing it to melt, but the temperature remained below the freezing point for pure water. Salt (and other substances dissolved in water) will always lower the freezing point. This is why water in the ocean rarely freezes.