© 2003 David J. Ritchie
Permission is granted for use as long as credit to "The Website of David J. Ritchie" at http://www.DavidJRitchie.com/ is clearly given. Note: Play-doh ® is a registered trademark of Hasbro (http://www.hasbropreschool.com/playdoh/).
The goal is to communicate to the student the search for the answer to the question "Is there a smallest piece of matter?" and if so, "What is it?". A subsidiary goal is to communicate the scientific method as an way of exploring the world in which we live. By "scientific method" here I mean simply asking a question and then doing an experiment to find out the answer. This lesson plan was oriented towards students early in their third grade year and so I felt that keeping the sense of the scientific method to just that was appropriate for the age group.
When the splitting has occurred down to the smallest amount allowed by the plastic knife, the group is asked to stop and raise their hand to indicate that they have finished.
They are asked to bring their "smallest piece of Play-doh ® " (their Play-doh ® atom) up to the front of the room where they place it on a piece of paper on the opaque projector so that everyone can see it. Next to it, the instructor writes the number of times they had to split it to get it to this size. This is a good point at which to ask the members of the team whether they saw anything unusual happening during the experiment, etc. They are told that this is called "publishing the results of their experiment" to others -- in this case to the other experimenters (the students) and teachers in the room.
What you are looking for here is a student to say that the reason
they
couldn't split it into smaller pieces was that the knife was too
big. When (if) you get something like that, you say "yes!". You
then
describe that scientists make machines to split things into very tiny
pieces.
A 
machine at Fermilab
has been made to split things
into very tiny pieces to get the smallest piece of matter out. The
picture shows a ring called the "Tevatron" in the foreground, a ring
called the
"main injector" in the background, and Wilson Hall, a 16 story
building, near the intersection between the two. The Tevatron ring has
a radius of 1 kilometer (or 5/8-ths of a mile) and a circumference of
6.28 kilometers or about 4 miles around.
Near Wilson Hall, in an enclosure called the pre-accelerator, hydrogen atoms are torn apart using electrostatic fields (These fields are like the static shock that you receive when you shuffle your feet across a carpet in winter -- only much stronger). One part of the hydrogen atom (the proton) is sent into a tube (about four inches in diameter) that leads to the Main Injector ring shown in the picture. All the air has been pumped out of the tube so that it will not interfere with the protons. (Yes, that means that the tube without any air is more than four miles in length because it has to go through the entire Main Injector and the entire Tevatron without anything getting in the way.)
The protons, which would go straight if we didn't do any thing to
them, are
steered by magnets around the Main Injector ring. At a particular spot
on the Main Injector ring, the protons go through microwave cavities
(the tube without air is built right into the cavity). A microwave
cavity is like the microwave oven that you have at home except that
instead of
giving your food energy by heating it up, the microwave cavity gives
the protons energy by accelerating them (speeding them up) in one
particular direction.
The microwave cavities are much more expensive than the magnets are
to
make so that's why we arrange the accelerator to be in a ring. We want
to re-use the microwave cavities over and over again. We send the
protons around the Main Injector ring so that they go through the
microwave cavities many times. After enough times, they end up
getting lots of energy which means they are going very fast. After they
are going as fast as the Main Injector's magnets will allow (the speed
just below where the magnets could not keep them in the Main Injector
ring), they are switched into the Tevatron ring. In the Tevatron, the
same procedure is repeated until they are going as fast as the strength
of Tevatron's magnets will allow.
The number of protons in the Tevatron at this point is about 10 Million Million (a 1 with 13 zeros after it). The speed of the protons is very close to the speed of light (186,284 miles per second = 300,000 Kilometers per second). This means they go around the Tevatron's 4 mile circumference about 50,000 times a second (186,284 divided by 4.).
When numbers of protons and speeds are just right, we make the protons hit particles going the opposite direction in the same tube. The particles going the opposite direction are anti-protons and are made in a different part of the accelerator. They have previously been put into the Tevatron where they circulate just next to the protons going the other way. By adjusting the magnets, the two circulating beams of protons and anti-protons are made to collide at a few spots around the Tevatron.
The protons are our knife. The anti-protons, which were there first,
are what our knife is
splitting. The
pieces that come out give us clues as to what the protons and
anti-protons are made of.
I did this unit with two combined third grade classes and two teachers and one teacher's aide. The group consisted of 40 students--two-thirds boys and one third girls.
Based on the letters from the kids, they really enjoyed it. They liked the "hands-on" part the best. They also seemed very impressed with my having come in on my "day off" to speak with them about splitting atoms..
I was worried as to whether the kids would become engaged with the activity or just use it as an opportunity to play. They became very engaged. I and the teachers tried to make sure that the teams of four were giving everyone on the team a fair chance to do some of the splitting--particularly, that the boys were giving turns to the girls but also that some of the more shy kids were being given a chance.
After all the teams published their results and we discussed what was going on and how Fermilab was an instrument similar to their plastic knife for splitting things (this took about a half-hour or thirty-five minutes), I just answered questions. There were some really good ones:
These questions lasted for some fifteen minutes and then the unit was over--having lasted approximately 50 minutes. Based on their letters and the reactions of the teachers (and anecdotal comments from one of the mom's), the unit was very successful and seems to have stuck with them.
The cost for ten regular size containers of Play-doh ® was approximately $12.95 at the local K-mart. Though it wasn't necessary for this unit, I was able to find Play-doh ® in ten different colors. I thought that it might turn out to be relevant in the lesson; however, it wasn't. By the time the Play-doh ® was split down to its smallest piece, it all seemed to be the same color regardless of what color one started with. (Actually, come to think of it, that is an interesting observation and experimental result that one of the students might have made.) That might go on a list for further investigations. Making up and having such a list would be a good thing to encourage the students to do in the lesson as it motivates being careful about observing -- you can develop a proposal for your next experiment while you are doing the current one.
I would like to thank Naperville School District 203's Ellsworth Elementary School
Third Grade Teachers Bruce Randolph and Katherine Smith for inviting me to conduct the "Splitting the
Play-doh ® Atom" unit and acknowledge their efforts in
conducting the lesson with me. Additionally, I would like to thank
Ellsworth Principal Sharon Ligman for her continued support. Finally, I
would like to thank Eric M. of Mr. Randolph's Third Grade class for
recommending me to his teacher as "someone who knows a lot about
splitting atoms."