DL-Fluid Mechanics

Demo - Pascal vs psi.  I show students just how small a Pascal is with a 1 N weight and a square meter, and how big a psi is with a 1 pound weight and a square inch.

Demo - Cubic Meter - I hand out 12 meter sticks and have 6 students hold up a cubic meter.  I point out it is 1000 liters - 1000 smart water bottles would fill it.  It would have then a mass of 1000 kg, so the density of fresh water is 1000 kg m^-3.  I also like to point out that the air in that space has a mass of 1.2 kg - which is fairly substantial.  If you compressed and cooled it to largely liquid nitrogen, it would occupy a cube about 4.5 inches on a side.  A Semi at highway speeds pushes about 400 cubic meters aside per second - which is about a half a ton of air per second.  Airplanes fly at 30,000 feet to find thin air.

Demo - Volume Estimation - I have students predict how high the Smart Water bottle will fill the graduated cylinder, and then how many times the cylinder will fill the (10 cm)^3 cube.

Demo - Balloon in a Bottle - you inflate a balloon in a short necked Florence flask with a pluggable hole in the bottom.  If you inflate the balloon, plug the hole, and take your mouth off the balloon, it stays inflated.  I mention an interesting demo that Chemistry Teacher George Penk showed me where he put He gas in the space between the partially inflated balloon and the glass.

Demo - Madonna, I mean Magdeburg Hemispheres - the classic demo of atmospheric pressure.

Demo - Can Crush - When you invert an aluminium can full of water vapor into cold water, the water vapor instantly condenses, and before water from the bucket can rush in to fill the vacuum, the atmospheric pressure outside of the can crushes it.  You really want the water boiling like crazy before you do this. (It's dramatic)  Dr Stan at UO does this with a giant steel barrel.

Demo - Density of Diet vs Regular Coke.  A can of Diet Coke floats - Regular Coke sinks.  

Demo - Two boxes - one full of air - the other full of gravel.  Hand the air one to a kid, and then casually hand the gravel one, and they will drop it.

Demo - Hillbilly Level - A siphon between two beakers keeps the water in each at the same level

Demo - Water Level Tubes - The water stays at the same height despite the geometry of the container.

Demo - Hot air Balloon - A paperclip weighted trash bag over a toaster.

Demo - Two Ton Jack - I demonstrate a hydraulic jack in the context of Pascal's Principle.

Demo - Mazuku.  I generate CO2 with baking soda and vinegar, and pour just the CO2 it into a jar with a lit candle, putting it out.  I show the Mazuku video on YouTube.

Demo - Cartesian Diver.  Classic.  I ask the kids if it is possible with a static clamp to have the diver stay right in the middle.  (It's not stable)

Demo - Egg in the Middle.  I have a cut off Smart Water bottle with an egg floating stably in the middle.  (The trick is that the bottom is salt water, the top is fresh.  The egg floats in salt water, but sinks in fresh.)  I talk about estuaries where the salinity varies by depth.

Demo - Hydrometers - I put a hydrometer in water, and another in a saturated salt solution.  The hydrometer doesn't have to sink as far into the salt water to float.  

Demo - Ice Melt -Will an ice cube melt faster in ice water or salt water?  Have them make predictions, put it under the Doc Cam and watch.  It's surprising and not what you think.  The answer lies in density and convection - which you can visualize if you repeat the demo, but this time put a couple of drops of dye in next to the ice cube.   Kosher salt is much more clear dissolved in water than the iodized easy flowing stuff.  I usually make up a flask of saturated salt water for this unit.

Demo - Venturi Demo - the air pressure drops in a constriction where the air must go faster

Demo - Bernoulli Straw - I use a blower to blow across the top of a tube in colored water.  The atmospheric pressure pushes the  water up the tube because of the Bernoulli Principle.  I moisten the kids in the front row accidentally.

Demo - Why Does the Pressure Drop in a Constriction? - I just outline why there has to be lower pressure in a constriction using Newton's Second Law.  I saw this in Lewis Carroll Epstein's book "Thinking Physics" which I highly recommend.  I think the Cartoon Guide to Physics explains it too.

Demo - Ball And Funnel - the ball in the funnel stays when you blow through the funnel because the air is moving faster behind the ball, and therefore the room pressure is more than the pressure behind the funnel

Demo - Blower and Cardboard - Air from a blower makes a sheet of cardboard adhere to a whiteboard because of the Bernoulli Principle.  I first demonstrate the force of the air stream by showing how it pushes the cardboard away - but when you press it against the whiteboard, and the air is rushing behind it, the room pressure is more than the pressure behind it.

Demo - Two Billiard Balls - you blow air between them and they move together because of the Bernoulli principle

Demo - Ball on Blower - The Classic - a ball will stay in the stream of air because the pressure outside the stream is higher than the pressure in the stream

Demo - Sheet of Paper - Blow across the top of a sheet of paper and it will rise.  If you blow hard enough, it will flap in the wind.  This is related to Kelvin Helmholtz instability  - so I show them this video:

https://www.youtube.com/watch?v=qgamfo86FQo

Which explains more than most 5 minute segments of any class ever.

Demo - stuff

Lab - stuff