Saturday, February 22, 2014

Particle Diffusion (Water and Food Coloring)

So, I may have overestimated SK's attention this week.  We had a good time, but her questions and observations went to a different place.  But, hey!  This is science, not cooking.

First, the science.

All matter is made of molecules.  These molecules are constantly in motion. The motion is random...that is, the movement of each individual particle is unpredictable.  As we zoom out, the pattern holds.  The phenomenon was first observed in 1827 by Robert Brown.  He observed pollen grains in water.  Today, in his honor, we refer to it as Brownian motion.

As we continue to zoom out, the sum of the speed and direction of these particles (physics and math people call these vectors) equal zero.  This makes sense.  The chair you are sitting on, stays a chair.  Its solid.  Even though its particles are in motion, together they stay relatively still.

That's great, but what does this have to do with food coloring?  I thought we were going to make frosting!  Actually, so did the Science Kid.

Stick with me.  Even though the sum total of the particles motion is zero, if there are different types of particles in a mixture, they will ultimately mix.  This process is diffusion.  Particles move form an area of high concentration to low.  You've experienced this when someone wearing to much cologne walks in a room.  Those closest to the offender begin to cough and snicker.  Over time, the cologne diffuses until everyone in the room can smell it.

We took it a step further.  When temperature increases, so does the speed of these particles.  At some point, the speed becomes so great, the molecules of a solid break apart and become a liquid, and then ultimately a gas (some day we'll get to phase changes, don't worry!).

Lesson over...on to the fashion report.  We got safety glasses for today.  Knowing the SK, I knew what I had to do: PINK!  No magic wand or lab coat, but Doc McStuffins was represented on the T-Shirt.

We started with tap water in a glass.  We put two drops of McCormack's Food Coloring (I tested my fancy organic food coloring gel ahead of time and it took FOREVER to dissolve) into the glass.  Instead of stirring, we watched the drops spread throughout the glass.  We talked about how pieces of water, called molecules, were moving all about. SK was not that into it.  She REALLY wanted to stir, so we stirred.  I pointed out the the pieces of water were moving even faster, and that the pieces of food coloring could mix faster.

Next, we did the same with near boiling water.  I explained that the molecules of the hot water were moving SUPER fast.  We watched the food coloring diffuse quickly.  This actually caught her attention, but first more stirring.

Now, we tried water that had been chilling in the fridge.  "If the food coloring spread quickly in the hot water, what will happen in the cold water?"  "It will go sloooooowwww!"  And, so it did.

I then asked her if we were done, but of course we weren't.  There was one more color, so I asked what type of water we should use.  SK thought about it, and said warm.  Makes sense, we did hot, tap and cold water, so warm was next.  Turns out she just wanted to stir more.

Today's lesson may have been more for me, then for SK; go where the questions take you.

So, your homework:

  1. Was your SK into it?
  2. Did you try anything other than different temperatures of water?
  3. You could even try measuring the temperature of the water or measuring the seconds it takes for the the food coloring to diffuse.
There you go...Time to Science!

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