Sticky Water
1. News flash: water is sticky. This is a surprise to many people because water does not seem sticky. In fact, it's the first thing that people reach for to wash away stickiness and any other kind of dirt. The second item, of course, is soap.
2. Water and things like glue are sticky in different ways. Glue is sticky in two ways. Water is sticky in only one way. Glue feels and acts sticky. It is used to join objects such as paper, wood, and plastic together. Water does not feel or act sticky.
3. Glue is sticky in two ways. One way is called adhesion. This is when glue, after it is poured on a surface, spreads into tiny holes and dents and hardens. The glue holds the surfaces together like the pieces of a jigsaw puzzle. But for glue to work well, it also needs to stick to itself and hold together. This is called cohesion.
4. Water does not have adhesion. If you pour it on a piece of wood, the wood will absorb the water, but water will not harden to make two things stick together. Water does have cohesion. Water is a unique substance made up of two elements: hydrogen (H) and oxygen (O). Water is made up of two parts hydrogen and one part oxygen. The formula for water is H2O. The hydrogen atoms not only stick to the oxygen, but also to other water molecules, much in the same way magnets stick to metal. Water molecules stick to each other because of "hydrogen bonds." If water did not hold together, it could not be a liquid. It would boil and turn into steam.
5. To see the "stickiness" of water, try the following experiment. This experiment is not dangerous, and it only requires ordinary objects that you probably have at home. However, you will end up spilling some water, so ask an adult if it is okay to do the experiment before starting.
Sticky Water Experiment
6. You will need the following for this experiment:
One short plastic cup (the kind adults use at parties for punch works very well)
One small pitcher of water
At least 20 pennies
A sponge or rag for spills
7. First, fill the plastic cup with water from the pitcher. Make sure you fill the cup all the way up to the rim. Don't spill any water! If you spill water, wipe it up. Make sure the very full glass is sitting on a dry spot.
8. Next, carefully slip a penny into the cup and look closely. Did any of the water spill over the edge? Probably not. Continue adding pennies slowly to avoid splashing. Slip them in gently. Do not throw them in.
9. Keep putting in pennies until water spills over the edge. How many pennies did it take for the water to spill over? It was probably more than you thought. Most people who do this experiment think one or two pennies will make the very full glass spill, but usually it takes more than 10 pennies. The explanation for this is cohesion. Each time you put in a penny, the water molecules hold on tighter and tighter to each other. Finally, when there is absolutely no more room in the glass and they're hanging over the edge of the glass, the water spills. One time, a scientist was able to get 25 pennies into the glass before it spilled! Now that's sticky water!
The author started the story with the phrase "News flash" to attract the readers' attention. The article is about a scientific fact. It is not a breaking news story.
Cohesion is a kind of stickiness in which molecules stick to each other via attraction, much in the same way a magnet sticks to metal.
The point of the experiment is to see how many pennies it takes for an already full glass of water to overflow. That is why the glass must be in a clean, dry place.
Water is sticky because its molecules stick to each other.
A paper clip can float on top of water because the molecules are stuck together and can hold it up.
