I try so hard to model an interest in science, and not just for the kids. Many of my closest friends and family are doctors or science geeks.
My concerted efforts notwithstanding, every once in a while I end up arguing a losing battle.
Early in our relationship, my future husband and almost medical school graduate and I found ourselves in a heated battle over Bernoulli’s Principle. We were on a white water rafting trip in Nepal, and I dared to suggest that we were about to travel uphill.
To this day, twenty years later, my husband never fails to remind me that water can NEVER travel uphill because of something proved by Bernoulli’s Principle. Of course, I never fail to look for instances where it can travel uphill. For all I know, my husband may be totally wrong about this application of the supposedly empirically proven scientific principle.
Anyway, this past week, I embarrassed myself yet again in front of a den of nine-year-olds. Somehow I mixed up an understanding about the three states of matter, and how liquid molecules spread apart when heated, so that vapor takes up more room than ice. I think that’s right, no?
Well, I took that to mean that water in solid form should take up less space than the same in liquid, until the den reminded me that a can of soda explodes in the freezer.
This morning, when we discovered the carcasses of delivered milk bottles that had been left out overnight, Dave graciously reminded me that this proves conclusively that a frozen liquid does take up more room than its liquid counterpart.
Just as graciously, I reminded him that there are instances where water does run uphill. Is it petty of me to have saved these photos from our trip to Blue Spring State Park for just such an occasion?
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{ 7 comments… read them below or add one }
Actually, you’re not totally wrong on both counts.
1 – Water can run uphill if it has sufficient pressure and is in a channel or vessel to prevent it from moving to a lower energy state. This normally doesn’t happen in natural settings, but to say it as a general principle isn’t true, either.
2 – Water is actually a bit unique due to its high polarity. Because of this, it will tend to form a crystaline structure as it solidifies which actually takes up more space than the liquid form. The reason the liquid form is smaller is because of the v-shape of the molecules which slip past each other in liquid form but create a lattice in solid form.
If you take carbon dioxide, however, it is actually denser as a liquid and thus will have a smaller volume. You can look at a phase diagram for a substance to determine which it will be. The slope of the solidus (the line below which a substance is solid) tells whether the the volume increases as the substance solidifies, which is shown as a solidus with a negative slope, or decreases, which is shown as a positive-sloped solidus.
So you obviously DO know what you’re talking about!
What a relief! As my son’s primary educator, I’m always worried that I might scar him with my nonscientific utterances.
Sandra,
Ditto Cherish. Water is one exception that its frozen state takes up more room than its liquid state because of its very high polarity. It forms a crystalline lattice structure upon freezing to keep like-charged atoms as far apart as possible. Sodas, milk, etc. expand and explode when frozen in inflexible containers because they contain so much water.
Try putting a small beaker of 151 rum or 200 proof Everclear in a glass with straight sides. Fill it about half way. A jar can be used instead of a glass. Measure the height of the alcohol freshly poured either with a mark on the glass or with a ruler, then cover it and put in the freezer over night. One, it won’t freeze all the way if at all. Two, it will contract just a little bit. The higher the alcohol content the more dramatic the demonstration will be.
Polarity is also why water boils at a much higher temperature given its structure than say ethanol, which has a higher molecular weight.
Water only runs down hill when the only force exerted on it is gravity. When water is under pressure from being in a channel, or being pumped through a pipe, gravity is not the only force exerted on it, and it will run up hill if the pressure force exceeds the gravity force. Please tell your husband that water in a fast-moving, narrow stream with lots of rocks can indeed move up hill because the water pressure force exceeds the force of gravity.
Sherri
Scientific principles always apply, but you have to understand all the principles at work in your system.
Bernoulli’s Principle isn’t the only law of physics at work in the stream. There is a net force that exceeds the gravity force and that net force is caused by water pressure.
Specific chemistry principles explain the exception of water’s freezing behavior and boiling temperature.
Science always applies. The question is which laws are at work.
Sherri
Thanks, Sherri! This is great example of why it takes a village to raise a child. No one person can possible know & understand everything.
We’ll definitely try the rum experiment. Wikipedia seems to have a good graphical explanation of polarity. Can you think of a better resource for explaining this concept to my son?
http://en.wikipedia.org/wiki/Chemical_polarity
Sandra,
The wikipedia explanation is fine. Actually it’s a bit complicated as a starting point.
I would start the demonstration on polarity using some bar magnets. When two ends of the same polarity are brought together, they repel each other. When opposite polarity ends are brought together, they attract and stick together.
Then I would go into the polarity of atoms in ionic molecules.
Thanks for bringing up this topic. It’s great to get to talk about my primary passions of chemistry and physics!
Sherri
Girl,
You fought over those topics with your then, boyfriend?
The fights I had with mine were always about who was gonna pay for the ice-cream during the date.
I gotta hand it to you–this blog was an educational lesson in disguise!
Keep up the good work!
Nando