# Other fluids education resources II – online videos

There are far too many videos out there to list here. Below is a list of some that I use in class. Obviously FYFD! has links to others. I apologize if some of the links die. I have mixed opinions about using videos in class. They can provide a break, show interesting phenomena, and surprise students, but they also are hard to directly, quantitatively re-connect to the class material, that is, they are often hard to analyze.

Shear thickening fluids – this is a fun video of people running over or settling into a paddling pool filled with water and corn starch. I used to make up a batch in a pain can for students to stir, but only very few students bothered. I think this is one case where the video is more effective for demonstrating a shear thickening fluid.

Surface tension and bouncing droplets – I know that I do not understand all the physics going on here, but my students always love watching the tiny droplets re-bound.

Momentum and jet packs (see also jet pack fail and the cheaper version) – This is one case where you can do some analysis. If you look around online (mainly on the manufacturer’s website) you can find the weight of the pack. If you add to that an estimate of the weight of the person then you can find the force required by the jet pack to keep the person airborne. The nice thing about this jetpack is that it is a steady flow. There is no fluid stored in the pack so the weight does not change with time. If you estimate the diameter of the intake hose and the outlet nozzles you can use the momentum equation to estimate the required flow rate. It is then possible to estimate the power required to operate the pack (that data is also available on their website). Of course you could always buy one for ~\$70,000 and demonstrate it yourself.

Drag and rowing – I use this to discuss drag and the power required to overcome drag. Some level of analysis is possible here. The simple version is to write down the drag equation and explain that the power required is the velocity multiplied by the drag and therefore the power scales on the cube of the velocity. This result can be used to explain why races are often very close as a 1% increase in speed requires a 3% increase in power. It is possible to go into a little more depth if you estimate the surface area of a rowing shell and the frontal area of the rowers. Treat the shell as a smooth flat plate boundary layer drag problem and the rowers as a bluff body drag problem. You will need a velocity estimate (about 6 minutes for 2,000 m is decent for a good crew). From there you can estimate the power required per rower.  A more humorous rowing video is here.

Drag and ember flight – Ember flight from wild fires is a major cause of home destruction. The embers are lofted and transported downwind by aerodynamic drag forces. There is not a whole lot of analysis to do here, but it is a nice video put out by IBHS and is another example of the application of the drag.

Drag and wind loading on houses – This is another IBHS video. It is a lot more dramatic than the ember flight video. IBHS has a very big wind tunnel in South Carolina and they use it to look at building safety in strong winds. Here they show two houses built to slightly different standards. The video is a lot of fun, but there are also some nice details. For example, in one version of the video there is a moment when the front door blows in. almost immediately the side door blows out and the roof lifts off (due to the internal pressurization of the house). After that it is all over and the house collapses.

For those of you who teach stormwater classes there are videos of

A culvert failure – The video shows the gradual failure of a culvert and resulting road collapse during a storm. The culvert is in trouble right from the start of the video, but the major problem is when a tree is swept into it. It is a fun video to watch, but is also good for discussing failure. I pose the question to the class “is this is a design failure?” It is often a good discussion and the answer is always that there is not enough information. Was the storm in excess of the design event? Was the culvert designed correctly but not maintained? Was the culvert designed correctly but upstream development increased the risk of higher flow rates?

A highway storm sewer failure – Like the culvert video, this is a lot of fun to watch. It is also very dramatic when the 6’-8’ access hole cover gets lifted up into the air and lands on some ones truck. It is a good lead in to discussing HGL analysis of storm sewers. Unfortunately the resolution is quite poor.

The Toowoomba floods from 2010 – I mainly show this because I like listening to the Australian accents on the voiceover. It shows a very dramatic flash flood in Toowoomba, Australia that came from a thunderstorm. It is not clear if the thunderstorm was a design event, but it did occur a day or two after a cyclone (hurricane) came through the region so the soil was saturated and everything ran off. It is a nice video to start off a stormwater class, or to lead into a discussion of the differences between event and continuous modeling of stormwater events.

An index of all the demonstrations posted on this blog can be found here. Don’t forget to follow @nbkaye on twitter for updates to this blog. If you have a demonstration that you use in class that you would like to share on this blog please email me (nbkaye@clemson.edu). I also welcome comments (through the comments section or via email) on improving the demonstrations.