## Tuesday, August 5, 2014

### Lab Activity: Hydraulic Jump => finding parameters

Lab Activity: ‘Deep Thinking’ and Parameterizing a Phenomenon: What Does it Depend on?

Goal: We want to gain practice and experience of how to think about and break down a phenomenon or physical situation/event as a scientist would. We will do this using the hydraulic jump.

Why do this?
Most people are not ever formally trained to think about things or observe things as a scientist. Part of the reason is there is no one correct way of doing this. However, one thing scientists tend to do naturally is, when seeing something that is interesting and perks the curiosity, not just to be satisfied with saying it is cool, but rather begin thinking about the parameters the phenomenon depends on.

To really know and understand how something works or behaves the way it does, a scientific study will require observations and measurements of controllable variables, i.e. experiments, which are determined by the physical parameters of the problem. If we can get good at determining the parameters, then this opens the door to a variety of possible studies and experiments. In physics in particular, doing this also opens the door to the development of mathematical models of the system.

Here I am using the definition of parameter = measurable factor on which the phenomenon depends. If it helps, think of it as an independent variable.

How will we do this?
We will spend a few minutes looking at and thinking about a simple, everyday phenomenon, which is also one that we do not fully understand to this day: hydraulic jump.

What to do:
Not much in the way of procedures on this one. To form a hydraulic jump, pour water on a hard, flat surface. That’s it! Then, observe, ‘play’ with it, and think about it.

What does your team need to do?
Observe the jump and ‘play’ with the experiment in any ways you can think of, and develop a list of as many possible parameters as you can think of. That is, what physical quantities might affect the properties and behaviors of the hydraulic jump?

One example that will probably stand out immediately is the flow rate of the stream of water. But think deeper than the obvious – what else might affect the jump? Who cares if it ultimately turns out some more obscure parameter does or does not affect the jump, write down anything and everything that comes to mind, even if you are completely unsure of its effect! There are no wrong answers to this part of the activity!  J

Team Brainstorm: Possible Parameters (just list them! You have 10 minutes)

Class Brainstorm: Possible parameters (anything other teams came up with, and you did not)

This is a process many scientists use to develop their research programs. By carefully dissecting a single phenomenon or event or situation, into an ideally exhaustive list of possible parameters, they can then begin to figure out appropriate experimental designs to determine the effect of one or more of the parameters on that phenomenon.  From the data of those experiments, mathematical fits can be done and empirical mathematical models developed. And so on. We will gain experience throughout the program at doing all of this!

Now it is your turn to try this – you knew this was coming!

In the next three days and with a partner, find a phenomenon, event or physical situation that you are curious about. It needs to be something that is ‘everydayish,’ like a hydraulic jump. It needs to be something that we could do experiments on with accessible equipment, without the aid of something like the Hubble space telescope, a cancer research facility, or a particle detector at Fermilab or CERN

Spend a small amount of time and play with that phenomenon. Make your list of physical parameters that may have an effect on the phenomenon. Be as thorough as you can, using what we just did as a class as a model.

In addition, based on your initial ‘play’ with the system, which parameter has the most significant effect? This may or may not be correct, but which parameter stands out as the most important?

Have fun, and try to find something interesting, perhaps unusual!

To turn in: A description of your phenomenon/situation/event, your brainstorm list of parameters, and a preliminary guess of the most prominent parameter (think about what would you want to test first). Feel free to add photos, diagrams, etc., to show the rest of us what you are talking about.