Friday, December 24, 2010

A Fluid Christmas Tree

   In the previous post (Fluid Play for Young and Old), you learned that food coloring is heavier than water and falls through water, in a straight line, with little mixing, just like salt and sand falls through air in a stream. A more accurate term than 'heavier' is density.
   Density is the mass per unit volume of a substance and provides a method for directly comparing substances. The volume of a kilogram of marshmallows is much much greater than the volume of a kilogram of lead. Therefore, the density of lead is greater than the density of marshmallows. 
   In this activity, the food coloring is denser than water but salt water is denser than both the food coloring and water.
   Gather the kids and the following materials and let them grow a fluid Christmas tree.  You may want to do the cutting for the kids and let them take over once you have the apparatus ready to go.                         

Materials
Glass eyedropper
Green food coloring
Card stock 2-inch square
Plastic margarine or whipped cream top
Two-liter bottle, empty and clean

   Depending upon the ages of your young learner's, you can either prepare the apparatus or supervise their doing the cutting and punching.
• Cut the top from the two-liter just below the curve of the neck
• Trim around the neck so that the neck sits level (see picture)
• Cut a straight line to near the center of the plastic lid
• Punch a 1⁄4-inch hole near the center of the lid
• Cut a two-inch square of card stock or thin cardboard and punch a hole near its center
Now it’s time to setup the apparatus to grow the tree.
Ask the kids to:
•   Pour enough water into the plastic two-liter bottle to so that it is about 1⁄3 full
•   Add table salt, one teaspoon at a time, stirring constantly, until no more will dissolve
•   Let the water sit for about 15 minutes
•   Place one hand, palm up on the surface of the water and carefully pour tap water into the palm, raising the hand to keep it on the water's surface, until the container is almost full (important – do not stir the water!)
•   Slip the glass eyedropper through the hole in the cardboard square
•  Half-fill a teaspoon with red, blue, or green food coloring and use the eyedropper to suction up as much food coloring as possible
•  Place the bottle neck over the hole in the lid and carefully set the eyedropper in the bottle’s neck

   Soon, a thin stream of food coloring starts flowing from the tip of the eyedropper. If there's an air bubble in the tip, gently and slowly  squeeze the rubber bulb until the food coloring starts flowing. 
   For the first few minutes, the green food coloring looks messy, as shown in this picture. Notice that the food coloring is still being contained vertically.
 
   After an hour or so, the food coloring appears to be collecting in a blob near the bottom of the bottle but is not mixing with the greater volume of fluid.
    Now, everyone can do other things while the tree grows. It takes about four hours for the tree to grow but, as the following picture shows, it's well worth the wait. After an hour or so, the food coloring appears to be collecting in a blob near the bottom of the bottle but is not mixing with the greater volume. As the tree grows, the horizontal branches broaden.
   As Christians, Christmas is the time we celebrate the birth of our savior, Jesus Christ. Grandadscience and grandmother math wish every believer in the the true meaning of Christmas, a very Merry Christmas.

Postscript
This 'tree' effect was demonstrated by grandadscience and a prominent Los Alamos physicist at a conference of fluid dynamicists. Attending physicists were challenged to offer an explanation but to date, none has been offered. Certainly the collision of the higher density food coloring with the even higher density salt water is at the heart of the effect.

Sunday, December 19, 2010

Fluid Play for Young and Old


   If you’re fortunate enough to spend time with the grand kids (or your kids) this holiday season, here’s a science activity that’s easy to set up, quick to do, and extends the kids scientific knowledge about the states of matter.
   Kids learn that matter exists in one of three states: as a solid, a liquid, or a gas. They are taught a set of characteristics they can use to distinguish one form of matter from another form. For example, a characteristic of a solid is that it holds it shape. It's a characteristic of a liquid that it takes the shape of its container. A gas also takes the shape of its container. Taking the shape of its container becomes a method for distinguishing a solid from a liquid.
   But a solid can exist in many forms. Take a rock, hit it with a hammer to break it into smaller rocks, pound the smaller rocks into sand, and grind the sand into a powder. But sand will fill the shape of its container and also pours, like a liquid! A powder can also take the shape of its container but, unlike sand, does not flow like a liquid! 
   To the scientific eye, there’s much more to learn about the states of matter than just classifying matter as either a solid, a liquid, or a gas. It's time for the kids to explore!
   Ask the kids to fetch the carton of table salt from the cupboard. Tell them to lift the spout and pour a small amount of salt into a cup. 

   Ask them:
   “Is salt a solid or a liquid?” [solid]
   “Which is heavier, salt or air?” [They will of course tell you that salt is heavier than air.]
   “Did the salt fall through the air?” [Yes.]
   "Does salt pour like a liquid?" [Yes.]
   "Why do you think the salt fell through the air?" [it's heavier than air]
   Ask them to fetch a small funnel and to put the salt back into the carton.
   Here’s a picture of sand streaming from the tip of a funnel. Salt and sand are called granular solids. To provide the kids another example of how a granular solid flows like a liquid, show this picture.

Materials
Glass eyedropper (if you have a plastic eyedropper, wrap thin  wire around the tip end so that it will float vertically)
Food coloring (use red, blue, or green, not yellow)
Two-liter soft drink bottle (remove the wrapper and use a commercial goo remover or citrus juice to clean off the glue)
      Have the kids follow these steps:
1.   Fill the two-liter bottle with cold tap water, all the way to the top.
2.   Half-fill a teaspoon with red, blue, or green food coloring.
3.   Use the eyedropper to suction up as much of the food coloring as possible.
4.   Carefully lower the eyedropper into the neck of the water-filled bottle (see picture) and wait.

5. Soon, the food coloring will flow from the tip of the eyedropper. Have the kids observe the motion of the food coloring.
6. Talk with the kids about what they've just done.
    The food coloring is slightly heavier than water so, like sand falling through air, the food coloring falls, in an almost straight line, through the water until the flow line becomes turbulent and mixing starts.
   In this science experience, food coloring, a liquid, falls through water like salt or  sand falls through air!
   To a scientist, a fluid can be either a liquid or a gas. An important branch of science is called fluid dynamics and fluid dynamicists study the  motion of fluids.
   In the next post, just before Christmas, I’ll show you and the grand kids how to grow a fluid Christmas tree in a bottle of water.


Tuesday, December 7, 2010

Grandmother Math in the Wind Tunnel

   In iFly, the early November 2010 post, grand kids Joshua and Jordan were featured flying in the vertical wind tunnel at iFly South Bay, near San Francisco.
   Our daughter Winona lives in Georgia with her husband, Dr. Gene, and our two wonderful preschool- age grand kids, Asher and Kate. Winona saw the iFly post announcement on the grandadscience Facebook page, viewed the post, and asked to see grandmother Math flying in the wind tunnel.
  Winona, here is the video.

Didn't she fly like a pro!