Tuesday, April 26, 2011

Simple Machines: Experiential Fun

The simple machines unit is a new one that I developed for the third grade.  They have a unit on simple machines in the classroom, and then build a simple machine in class.  These stations that I describe in an earlier post help them further their understanding of some of the machines.  I covered: levers, inclined planes, pulleys, and screws.  I worked the lever station, and had various parents and grandparent volunteers covering the other three stations.  In my station I found some of the kids had a really good understanding of how levers worked, and others really didn't understand them at all.  For example, I had three lever examples that I used: class 1, class 2, and class 3.  In the class 1 lever, I asked, "Where is the load easier for me to hold, at the end of the lever or in the middle?"  Often, the kids thought it would be easier to hold the load the closer I was to the fulcrum.  I let the feel it for themselves, they were often surprised.  I then asked them, "Is the load easier to lift if it is near the fulcrum or farther away?"  Again, even if they answered the first question right, they often assumed that the load would be easier to lift if it were farther away from the fulcrum just as it is easier to apply the effort to lift the load if you have a longer lever arm. 

One thing I found was that none of the kids had any experience with a spring gauge.  Before we started the station rotation, I showed them two different gauges and we talked about how they worked.  Then, they used the gauges in three of the stations to record information about how levers, pulleys and inclined planes worked.

We had two inclined planes set up:  one six inches high, and another twelve inches high.  We had them measure a load by hanging it from a spring gauge, then asked them to guess if it were easier to lift the load, or to pull it up an inclined plane.  Again, often the kids thought it was easier to lift the load even though they had finished a unit on inclined planes and should have remembered that the inclined plane is used to make moving the loads easier. 

Once they were finished with the experiments that I had written for them to do, we often had a bit of time to let them experiment.  You can see them using the spring gauges in the above photos.  One group decided to test my knowledge about inclined planes.  They set the plane up at a very high angle and asked me what I though the bag of rocks would do and why.  I asked if they were asking me to guess how much effort it took to lift the bag up the plane, but they said no, they wanted to know what I thought the bag would do at the top of the plane if they let it go.  It was at a high angle and it was apparent to me that it would slide down.  I answered that it would slide down.  They looked surprised that I knew that.  I asked them if they knew why it slid down.  We then had an impromptu discussion about friction.  I had this class last year run some experiments on ramps in which we had them slide things down a ramp, and then to slide the same objects down a ramp with sand paper on it.  I asked if they remembered the experiments.  They did remember them, and then I asked them why the object slid down the ramp with no sand paper and didn't slide down the ramp covered in sand paper.  Then the light bulbs went off.  It was a fun review lesson.  It is also fun for me to find that they remember the experiments from previous years.

The pulley station went well, but we did not have enough for them to do in that station.  Next year I think I will add a triple pulley.

The last station I had set up was one in which they compared coarse threaded and fine threaded bolts.  I had them turn a nut 20 times on each type bolt and then to measure how far each nut traveled.  We then had them make their own bolts our of pipe cleaners and dowels and to compare the paths up the dowel of the fine threads and the coarse threads.  Finally, I had two pieces of foam board, each one the same length as the pipe cleaner lengths that I had them make their screws out of and we talked about how hard it was to climb up one ramp versus the other.

Overall, these stations were a success.  I would use them again with a bit of tweaking in the pulley station to have them do more hands-on activities in that station.  I would remove the third class lever from the lever station.  The other two stations I would leave as is.

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