Science Buddies: "Ask an Expert"

Tireless Tides: Extracting Energy from Ocean Tides.

I am working on this experiment and encountered a situation where as the water was draining from the bucket, the water would change direction and instead of draining out clockwise it would change directions and drain out counterclockwise. I have searched the internet trying to understand this scientifically. Either I'm asking the question incorrectly or this was unique to my experiment but I can't find anything to define the situation. I know that I needs to write it up as part of my findings but would like to get more "science info" on it. Can you help me out and either give us a resource or the science name for the change in direction? Thanks

Hi DFalconer,

Did you observe this in all three holes, or just in one particular hole? If it only happened with one particular hole, then I would suspect that something about the way that particular hole was drilled or shaped is the cause of the direction switch. But, if you observed the switch for all of the holes, then I'll need to do some more thinking about what might be at work. Does this happen every time you do the experiment? Or only intermittently? One thought - are the bucket's supports level? The change in direction is probably related to the vorticity of the water. The math describing vorticity involves vector calculus, which is defintely beyond what I would expect for a middle school-level science project! Basically, vorticity is related to the spinning of a fluid (like water).

Looking forward to your reply!

Thank you so much for your help. Vorticity...no wonder I couldn't find it on the internet.

i apologize for the lack of details. My son modified the experiment to only have one hole - he wanted to focus on the types of propellers on his experiment....looking at different shapes ro see if one is more effective. The problem only occurred intermittently; out of a total of 15 trials only occurred twice. In his Data Anaylsis he wanted to explain the anomaly but was having trouble giving it a name and explaining why it happened. The bucket was completely level - I know that because he used a level when he set it up to ensure the water flow but we'll double check it. Strange this is that the bucket never moved. He just added removed the bucket from the bottom to dump back into the top to run the next trial. He had several propellers which he changed out by simply pulling up the propeller axle.

I think that your definition for Vorticity is the 100% dead on. We will do further research to be able to explain it on the project as well as at the judging next month.

Thank you so much for your post..Debbie

I'm glad it was helpful! And, kudos to you & your son for making the project your own.

Since the switch in direction happened occasionally, I suspect that it was related to an outside variable of some sort. If it were related to something in the experimental setup or procedure, I would expect the switch to have happened more frequently. It could be something as simple as the side of the bucket the water was added to. I think the thing to do is to note that this happened sometimes (which you did) and explain that you're not exactly sure what caused the switch to happen. But, that it may be related to some unknown factor(s) changing the vorticity of the water as it drained out of the bucket. That way you show the judges that you thought carefully about your experiment, and were able to suss out the important patterns from the background, chance variations.