Science Buddies: "Ask an Expert"

My 4th grade daughter is doing paper recycling for her science fair project. We have background research that says that repeated recycling reduces the size of paper fibers. (Something we can measure, great!) But, how do we measure the length of the fibers? We have a digital microscope that I'm guessing will be reasonably accurate for measurements from .25 mm and up to maybe 3mm (then the fiber would go off the screen). If the on-screen measurement doesn't work, the back up plan is to get relative measurements by printing off pictures (all at the same magnification level) and measuring with a ruler. (This would tell us which sample has larger fibers, just not their exact length.)

We put paper and water in the blender and attempted to make microscope slides, but the fibers are still very tangly and curly and hard to isolate to measure. Any suggestions how to untangle them enough to make sure we are measuring one fiber at a time? Also, the fibers clearly vary in length, so we will need to make multiple measurements and do an average or scatter-plot or something. Any suggestions what an appropriate data-set size should be for a 4th grade project?

--Janet

Hi Janet,

This is a great project, but you have already discovered that the measurement process for this experiment is going to be challenging. If you are doing an experiment where you need to measure the size of the particles, it would be best to measure 100 fibers. Doing multiple samples or 100 fibers each would exceed the patience of all of the 4th graders I know, so you will need to work with your daughter and determine how much time she is willing to spend on each sample without losing interest in the project. You want to encourage her interest in doing a scientific investigation and make sure this will be a good experience for her. So maybe 10 fibers for each sample would be a good number for a 4th grade project.

Using the microscope to measure the fibers doesn't sound like a good method since one fiber can fill up the entire field of view. Making a photograph and measuring the fibers with a ruler sounds like an idea that would work, you should be able to measure within + or - 1 mm. One idea would be to have more than one person in the family measure each sample to find out how reproducible the measure method is.

For a scientific approach, you need to pick a measurement method and fibers to be counted, and describe the method in the procedure section of the board. Then use the same method and count the same number of fibers for each sample. You can report the results as a mean for each sample, and show your daughter how to a bar graph to show the particle size distribution in the samples.

Donna Hardy