Building a Water Roller Coaster

A flowing siphon.
Water Roller Coaster #1

| Other Newspaper Projects | Water Roller Coaster #2 |

Parents, don't fret. This is perhaps the simplest bit of science that you will ever encounter - and yet one of the most profound in all science. You see, one of the things about Natural Laws is that they are usually supposed to be self-evident, and therefore understandable by even your preschooler - despite all the big scientific words that are attached to these laws. But remember that little children like to use big words, so why not let them amaze their cousins and friends! It'll make you look really good, too! So the big words are written here in red so that you can have a vocabularly list for your child, who probably cannot read or write very well. So YOU have to make the list!

What is nice about this exercise in the use of siphons or syphons is that it is simple and fun for kids who like to splash around in water.

Parental WARNING!
After your children do this experiment, hide the tubing or else you might find water flowing out of the bathroom as the tub is being emptied the wrong way!

Science for Parents

Everything in the universe is governed by just a very few laws - the Laws of Thermodynamics. In street language two of these laws might be termed: "everything prefers to run downhill," and "you don't get something for nothing." So what's new? These should sound very familiar to you and your life, right?! That's because you, are governed by these laws, too.

"Downhill Law" is formally called the Law of Free Energy or the tendency to - well - go downhill! Like I said: self-evident! And the more downhill the better - wheeeee! (But this is not all fun and games: hydroelectric power dams work on this principle, your wind-up clocks do too! And less obviously all submicroscopic chemical reactions do , and cosmic things in galaxies. EVERYTHING IN THE UNIVERSE - large and small. That's why the Laws of Thermodynamics are "universal" and are so important - yet, as "laws", they are so easy to understand.

Thus we get to this lesson on:

Siphons and the Downhill Free Energy Law

There are two goals in this exercise.

One is simply THE law: that of the tendency to go downhill - that the outer end of the tube must be lower (downhill) than the surface of the water inside the container.
The second is to show that the further down the siphon's exterior tube goes, the faster the water flows out.

Now, dear Parent, as your child's teacher and guide, it is up to you to put all this into words your child will understand, but don't be afraid of using the big red-letter words. Your child WILL understand these principles even though your child may be only 3 years old and too young to read. "Self-evident"! After you have run the "wet" experiments with the water, you might then want to ask you child to find the "downhill-ness" in a few other simple things in life such as dropping a ball or in another fun thing kids like to do - make pulleys and run string over things to pull up loads (see end of this page).

THE LAW of wanting to go downhill:
Starting a siphon: Of course you know that when you set up a siphon arrangement, the water will not start flowing on its own. (That's the gist of the next part of these Thermodynamics lessons!) Usually the easiest way to start a siphon flowing when the siphon is a small diameter tube is to position the lower end of the tube outside the container and BELOW the surface of the water, and then kneel down and suck on that end until the water comes. This assumes, of course, that the container, tube and water are all clean and fresh. Another way is to slowly snake the whole tube into the water so that the tube fills with water. Then plug your finger over the end of the tube and lift that end out of and over the rim of the container. Only release your finger from the tube's end when the end is lower than the surface of the water.
Observations: Water will only flow out of the tube IF the end is lower than the surface of the water inside the container. The child's attention should be focused on the water at the end of the tube AND the water at the surface of the container. Forget about how deep the water is in the container - that doesn't matter! If the water at the end of the tube is lower than the surface water - the surface water will want to go over the rim and downhill to be with the water at the end of the tube. BUT if the end of the tube is raised ever so slightly above the surface of the water, then the water and the end of the tube will want to go over the rim and downhill into the container.
Of course, the above could just as easily be demonstrated by placing a smaller paper cup inside of a larger one. If the smaller cup has a hole in its side, water will flow into the smaller cup IF AND ONLY IF the water level in the large cup is higher than that in the small cup. And vice versa. Self-evident!
If the two levels are the same, water will not flow at all. The system is 'in balance.' (This by the way, is what is called the "Zeroeth Law of Thermodynamics" - when the two sides are balanced, there is not net flow of energy or matter. Self-evident!)
Now, for fun, see if you can "balance" your siphon?*

Kinetics*

How can we measure how fast the siphon is flowing? The easiest way to do it is to see how many little paper cups of water can be filled in one minute. This will give your child two very important concepts - the value of counting numbers, and how those numbers relate to measuring something. Both of these concepts are so "self-evident" that you need only show the child how to do it, and the young mind will immediately take it in. Once the child has done it once with the tube at one position, have it done again at levels both higher and lower. As a quiz: ask two questions - (1) At which level did the water flow fastest? (2) How do you know that it flowed fastest at that level?

Now, here is something for you, Parent! Put on your thinking cap and think about this: why does it flow faster and faster the lower the end is placed? Is it because the water in the exterior tube is falling and, just like a car coasting down a hill, will go faster and faster? Let's think about a roller coaster. What would happen if the cars were not hooked together and went over the top? They'd all be pushed up to the top together - touching each other end-to-end, but as soon as the first car got to the crest it would break away and start going faster than the second car. Soon you'd see individual cars racing down the track but with spaces between them. Always car #1 would be going faster than #2, and #2 faster than #3. BUT the roller coaster cars are all hooked together - just like the water flowing through a syphon. So why do longer external tubes flow faster? Hmmmm!!! If you think you know the answer, click and send this website your answer. Hey, you as an adult can also exercise your brain while your child is happily making a wet mess on the porch while observing how Free Energy works!

Pulleys
A really astute child might ask: "If everything is ALWAYS supposed to be going downhill, then how do things get uphill?" Let's make use of broomstick that spans the backs of two back-to-back chairs. Cut a piece of string long enough to go from floor over the broomstick and just a little way back down toward the floor again. To one end attach a small weight - a small stone, for example (fig 1). By pulling on the free end of the string, the stone can be raised up to the broomstick (fig 2). And then, if the free end is let loose, the stone drops to the floor - as expected from the Downhill Law (fig 3).
1 2 3

With the small stone on the floor, now tie a larger stone to the free end of the string (fig 4). If the larger stone is let loose, it will go to the floor pulling the small stone up (fig 5). So that is how things go uphill - they have to be pulled uphill by something larger going downhill. You see the Downhill Law does NOT say that everything must always go downhill. The Downhill Law says that the average of everything in the system must go downhill (or be balanced!).
4 5

Hopefully you don't have an extremely astute child, who will surprise you sometime by asking: "What pulls a car uphill?" Up to now with the pulley system over the broomstick, you have been involved only with "matter." You must now explain to your extremely astute child about the sum of matter and energy, and the energies released in the explosions inside the car's engine. Maybe this is one of the many times you will have to say: "You won't understand until you are older and in high school where the big kids are!"

Next time
"Activation Energy" - the you-don't-get-something-for-nothing Law

* For the especially curious parent, we have so far talked only about the tendency or desire of the water to want to go in one direction of the other. We have not talked about the speed that water would go if given a chance. One of the many ways that the Physics "pie" can be divided is into two realms called "statics" and "dynamics." When nothing is moving (as in the potential to do something such as when the finger is still plugging the end of the tube), then we are speaking in terms of statics. When things are moving, we are talking in terms of dynamics - speed, momentum, acceleration, etc. Dynamics is subdivided. If we talk about the speed of things, we are talking about "kinetics." Thus part II, above, is thus titled "Kinetics."