# Water Properties

Water is wonderful. We drink it. We wash with it. We cook with it. We swim in it and boat on it. We skate on it in winter. It coats our lungs so we can breathe. Let's explore its properties a little this month.

Cohesion
How many drops of water can you put on a penny? Guess. Now try it. Get a penny and a medicine dropper. Put the penny on a desk or table and carefully start putting drops of water on it. How many can you put on the penny before it overflows? Does it matter if you drop the water from high up or from close to the penny? Does it matter which side of the penny is up? Are you surprised at how many drops will fit?

This property of water, the property of sticking to itself, is called cohesion. Try doing this same thing with water with a little soap in it. Does it work the same? Do you think soap changes water’s cohesion?

Put some water in a glass. Try setting a paperclip on top of the water. Can you do it if you are very careful? Try bending another paperclip into an L shape and using this to help you lower the paperclip onto the water. Can you get it to sit on the water now? Try adding a drop of soap or detergent. What happens to the paperclip? The paperclip was not floating, it was being held up by the water’s surface tension caused by the water’s cohesion.

Try putting one drop of water on a piece of wax paper. Put the wax paper over a page of the newspaper. Move the wax paper so the drop is right over one letter on the newspaper page. How does the letter look? You just made a magnifying lens using the cohesion of water.

Do other liquids show the property of cohesion? How could you find out?

Displacement
What happens to water in a container when you put things into the water? Get a cup of water. Put it into a large pan or into the sink so that you don't make a mess if you spill. Mark the side of the cup some way to show the level of water in the cup – maybe use a piece of masking tape. Now, put a penny into the cup. Add another penny. Add ten more pennies. What happens to the water level in the cup? This is called displacement. The pennies are filling the cup, pushing the water out of the way. Sunken pennies displace water. Do floating boats displace water?

Take the pennies out of the cup. Make a small, flat-bottomed boat from a piece of foil. Float it in the cup or a larger container. Be sure to mark the water level on the side. Carefully start putting pennies into the foil boat. What happens to the water level now? Sink the boat by pushing it down with your finger. What happens to the water level after the boat sinks?