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    • A kid looks at me and asks: "what do you do again?". What to answer? Do I bore her with the memory saving hacks I employ to reduce the computational load of a data assimilation scheme in the context of a global hydrological model? I can already see her suppressed yawn. So no, I do not answer her truthfully. I say "this is what I do!". And than I do experiments with her (not on her, that is unethical). Using stuff laying around. To show her what science is and inspire her.

      Monday april 13th I gave a presentation called "5 experiments in 5 minutes". I demonstrate five experiments that anyone can do together with kids. The presentation was recorded and I posted it under this blog.

      Below I wil describe the experiments done, so anyone can do them at home.

      Photoframe raingauge

      prototype acoustic raingauge (disdrometer)

      This experiment demonstrates how to make a copy of the first prototype of the acoustic raingauge that I am developing with colleagues in Delft.

      1. Ducttape glass pane of photoframe to top of frame using ducttape.
      2. Glue piezo-disc to bottom of photoframe.
      3. Solder audio-cable to piezo.
      4. Test raingauge by plugging it into anything that has a microphone input.

      A manual in Dutch can be downloaded here.

      Cake and booze hydrology

      This experiment explains why it is important to know different landscape types if you want to predict floods, which is what hydrology is (mainly) about.

      1. Get two pieces of cake with a dry cake layer and a water-resisting (hydrophobic) icing layer. I find that Starbucks Marble Loaf cake works perfect.
      2. Eat the frosting of one of the two slices of cake. Explain that the cake with frosting is like a city: hard pavements, and the cake without frosting is like farmland: soft soil.
      3. Use a spray bottle filled with a strongly coloured liquid (I use Blue Curacao liquor) and spray the top of the cake.
      4. Show that the frosting-cake has liquid running of it, and dry cake. The non-frosting cake has no standing water, and soggy cake. This is the differences between rain on a city and rain on farmland: rain on a city leads much faster to water in nearby rivers. So it is important to know landscape type when predicting floods.

      Making CO2

      This shows how to make carbon dioxide: CO2, which can be used to extinguish fires.

      1. Fill a 1 liter bottle with 250 millilitre of cheap but strong (cleaning) vinegar.
      2. Fill a balloon with 2 tablespoons of baking soda. Use a funnel if you have one.
      3. Put the balloon on the bottle, and hold the balloon above the bottleneck, dropping the backing soda into the vinegar.
      4. If you have a tea light candle and a small glass container that is barely larger than the tea light, you can extinguish the tea light using the CO2. Carefully remove the balloon. Any oxygen that was in the bottle at the start of the experiment is now in the balloon, since it is lighter than CO2.
      5. Carefully pour the invisible CO2 in the glass container to extinguish the tea light.

      Plasma cutter

      This experiment was thought up by the Slow-mo guys. (Or at least, I saw it first on their youtube channel). You can watch their video here.

      1. Daisy-chain (connect plus to minus) six 9V batteries.
      2. Cover a cup with aluminium foil.
      3. Connect a wire with crocodile clamps from the minus to the aluminium foil.
      4. Connect another wire from the plus to a pencil lead (which is made of graphite, not lead!). Touch the aluminium carefully with the pencil lead: plasma!

      Elephant toothpaste

      My final experiment is one that can be found all over the internet: making elephant toothpaste. Mixing hydrogen peroxide with liquid soap and adding yeast results in an explosion of very stable foam that looks like toothpaste that an elephant would use. I like this video, that focus on using ingredients that you can get at home. He uses clear-hair-developer as his source of peroxide. This one includes an explanation of the reaction and is much more spectacular, but they use 35% peroxide, which may be hard to get. Warning: do not get peroxide on your skin! If you do, wash directly away with water. Hairdressers do not use gloves without a reason when applying peroxide to peoples hair!

      So those are "5 experiments in 5 minutes". Have fun!