Goop by any other name....

Last week I started our round of engineering and science activities for the year.  I am kept busy this year with one to two sessions each week now that I have grades K-5 participating.  Recruiting volunteers remains a challenge...But onto the important stuff.

We started third fourth out this year making homemade silly putty.  I found three different recipes on the web and decided to let the kids test them out to find out which worked the best.  My intention, you know the idea, "the best laid plans..."  and "the road to h___ is paved" with good ones, did not result in what I had hoped.  Making the transition from teaching college kids to elementary school kids is challenging.  I forget how much they can take in at one time and still tend to bombard them with information.  In any case, I had intended that we test the three different formulas to see how they performed, and how well they mixed up.  I think the kids just got that they could mix up the putty and have fun and I am not sure they got anything out of it other than that.

I had intended that the take a logical approach to making and testing different formulations and scientifically decide which was better.  Control of the mixing and product was difficult.  Let me explain why.  Here are the three formulations we used:

	Formula A (red)	Formula B (green)	Formula C (blue)
Glue	1 teaspoon	1 teaspoon	1 teaspoon
Water	1 teaspoon	2 teaspoon	1 teaspoon
Borax Solution			1 teaspoon
Borax powder	1 teaspoon	2 teaspoons

When I did this at home I did not use food coloring.  I would definitely suggest you use the food coloring.  If you don't all the samples are white and it is really hard to tell them apart.

It makes for a bit more mess, but it is easier for the kids to keep up with everything.

First, we talked about safety.  Borax is a really safe detergent booster, but if ingested, a lot of it could make you sick.  There is that occasional child who likes to taste things....  We then talked about the attributes of silly putty.  The commercial silly putty is very stretchy, bouncy, and can take up images from newspaper really well.  I told them that these are the things we wanted to test for in our formulations.  I told them that we were looking for the best recipe for them to make again and to recommend to their friends.  Finally, I then asked the kids if they knew what a chemical reaction was and how to look for it.  They had covered this in class, and had several suggestions on looking for reactions:  blows up, bubbles, fizzes, changes color, smokes.  Very few had the idea that the mixture could give off heat.  I suggested they look for changes including heat. That of course is what happens when you mix the water and borax, you get some warming.

I then had the kids mix up the samples in the following order:  first mix the water and borax until it is really mixed up, last, add the glue and mix some more until it begins to ball up.  You can add the color at any time, but an adult should drop in the color.  We used two forms of borax: straight powder and a solution, which was 2 tablespoons of borax mixed with 1/2 cup of warm water.  The mixing process is a bit messy and can vary a LOT from child to child.  We did have some issues of the formulas not coming together or being too crumbly.  One child would have a great mixture, and at the next table the same formula would look totally different.  

Once the formulas were mixed and rolled into balls we tested them.

	Formula A	Formula B	Formula C
Bounciness	cm	cm	cm
Imprint Retention	sec	sec	sec
Stretchiness	cm	cm	cm
Pull
Ink Transfer	good  fair   poor	good  fair   poor	good  fair   poor

Again, as in the mixing of the formulations, the testing accuracy varied greatly.  I had the kids divided into teams of three and were supposed to work together the make the test the various formulas.  However, team work is hard for them.  They tended to work independently, but they had to help each other with some of the tests.

Here is a list of the tests we performed:

1. Form the putty into a ball and see if you can bounce it.  Using a meter stick, see how high the ball bounces when dropped from 1 m. high.  Record on Activity sheet.  Do this for each formulation.
2. Take your pencil or handle of spoon and make an imprint in the ball.  Record how long it takes for the imprint to disappear.
3. Roll each ball into a 2 inch rope and slowly pull the rope and record how far it stretches before it breaks.  How far can you stretch it?  Measure with meter stick.
4. Quickly pull each formulation and record the results.
5. Flatten into a pancake, using a sheet of newspaper, test how well each formulation picks up the ink off of the newspaper.  Can you read it?  Record the results.

There were a couple of problems with the testing.  Imprint retention was VERY subjective.  The idea was to let the students see that silly putty acts a bit like a liquid in that with time it slowly moves to take the shape of its container like a liquid.  Then, if acted upon quickly like in the pull test, it will break more like a solid.  I believe the kids were too focused on playing with the putty to think and compare their results.  

The stretch test was a bit easier to perform if the kids followed directions, which of course many didn't. We laid the two inch rope of putty on a meter stick and slowly pulled.  Overall this test went well.

Finally, I had newspaper laid out for testing transfer of ink.  None of these formulas really transferred any ink to speak of.

In the end, the kids were not able to detect a clear winner on which formulation was the best.  It was so dependent on how well the kids measured and mixed that we didn't really take away what I had intended from this lesson.  I am not sure how I would change this for next year.  

As for me, there was a clear winner in the three formulations shown above.  The one made with the borax solution was a bit messier to mix, but in the end was more consistent than the other two formulations.

One thought for next year is to let the kids decide how to formulate the putty using the following table:

	Control (red)	Formula A (green)	Formula B (blue)
Glue	1 teaspoon	1 teaspoon	1 teaspoon
Water	1 teaspoon	x teaspoon	xx teaspoon
Borax Solution	1 teaspoon	y teaspoon	yy teaspoon

One thought for next year is to let the kids come up with a variation on the control formula and use the borax solution approach.  I have not tested this procedure, but will have to look into it.

In any case, the kids had fun.  Half the battle at this age is to get them to have fun with science and engineering and to inspire them to learn more.  In that light, the activity was a great success.