Monday, April 18, 2011

Simple Machine Experiments for 3rd Graders

 My next engineering and science session is with the third graders.  The third graders in Virginia study simple machines.  Below is a portion of the science standards regarding simple machines.

The student will investigate and understand simple machines and their uses. Key concepts include
    1. types of simple machines (lever, screw, pulley, wheel and axle, inclined plane, and wedge);
    2. how simple machines function;
    3. compound machines (scissors, wheelbarrow, and bicycle); and
    4. examples of simple and compound machines found in the school, home, and work environment.
We will use four stations for this session:  levers, inclined planes, pulleys, and screws.  For the first station, we will look at the three classes of levers: class 1, class 2, and class 3.  In the first station using spring scales, the students will be asked to weigh the bucket of rocks as shown below.  I tested this station using 5 Newtons or 500 grams and a 1000 gram or 10 Newton scale.

 I use a broom stick without the broom attached, of course.  For the class 1 lever, an example of which is a see-saw or crowbar, has the fulcrum or support point located between the load and the force or effort which is where the students will place the spring scale to look at how much effort is needed to lift the load they first measured in step 1.  This result is dependent on where you place the fulcrum and where you place the effort, but for the example shown below we found the force needed to support the load was 0.7N or 200 grams.

For the second class lever, the load is located between the fulcrum and the effort or spring scale as shown below.  Examples of a second class lever include a wheelbarrow, nail clippers, and a stapler.  For the configuration shown below, the effort needed to lift the load was 3.7N.

The third class lever is shown below.  It is a rather strange setup that requires someone to hold the lever at the fulcrum.  The load is placed at the end of the lever, the support is in the middle.  This lever requires more force than the load weighs.  It takes 9 1/2 N to support the load of 5N.  This lever is used to gain leverage when more force is needed at the end of the lever.  An example is a pair of tweezers, where the tweezers can supply more force at the end to get out the splinter than you would be able to provide with just your fingernails.

The next station features inclined planes.  In this station, the kids will be asked to weigh a load using the spring gauge.  There is an inclined plane and the students will measure how much force is needed to pull the load up the plane with a height of 6 inches, and then to repeat the process with a height of 12 inches.  In the experiment shown below, I measure the load hanging on the spring scale as 210 grams, up the 6 inch incline as 100 grams and up the 12 inch incline as 120 grams.

The pulley station has two setups, one for a single pulley, and one for a double pulley.  This station will already be setup, the kids will measure the force needed to lift the load without a pulley, with a single pulley and with the double pulley as shown below.

The final setup will be for screws.  In this setup, I will have a dowel with five inches marked at each end.  The students will be asked to wrap the pipe cleaners around five inches of the dowel.

They can then see that the shorter piece takes fewer turns to go up the five inches, but is steeper.  I will also have two boards or pieces of foam board cut to the same lengths as both these pieces of pipe cleaner.  The students will be able to see that it takes less work to climb up the longer ramp than the shorter, steeper ramp, just as theoretically it would take less work to use a screw with finer screw threads than coarser threads, but it would take more time to screw it in. 

Finally, I will have the kids compare two bolts, one with fine threads, the other with coarse threads.  They will turn the nuts 20 times each for each bolt and see how far that translates into linear distance as shown in the photos below. 

If you would like to receive a write-up of this unit, please get in touch.

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