This is my version of a well-known activity: seeing how many drops of water will fit on the top of a penny before it overflows. This is a great introduction to the scientific process of testing a hypothesis. The lab report includes directions and a rubric. I have also included a short description of each part of a scientific report (Problem or Question, Research, Hypothesis, Experiment, Results, Conclusion, and Reflection).
One great thing about this activity is that the materials are inexpensive and easy to come by. This would be an activity that would work for a substitute teacher. I use this at the beginning of the year to talk about the ways scientists work and to give the students a look at how we will be presenting our findings throughout the year.
If you have not done this activity, it is fascinating. The surface tension of the water allows many more drops of water to fit on the penny that most students will hypothesize. Then when you repeat the experiment with some soap (any kind) on the penny, the soap breaks the surface tension, and the water overflows much sooner.
As an extension for older students, have them investigate what soap is. Soap has both a hydrophilic (water-loving) and hydrophobic/lipophilic end (water-repelling/oil-loving). This is what allows soap to work. One side of the soap molecule bonds to the oil in our clothes or on our dishes while the other bonds with the water and allows it to carry the dirt away.
For this activity you will need a penny for each student, a plastic pipette or dropper for each, and some paper towels to clean up. Any kind of soap will work for the second part of the experiment. If you have small graduated cylinders, it is interesting (and good practice) for the students to see how many drops of water are in 5ml. Note that the size of the drop depends on the diameter of the dropper, so keep that in mind (another interesting extension for older students). You don’t need a graduated cylinder for each student. I have them work in pairs.
If you want to incorporate some math, have a look at the data set of the number of drops each student counted in 5ml. This is also an opportunity to discuss sources of error. There may be variation in the size of the drops, and there are also sources of user error in reading the graduated cylinder and counting the drops.
I have included both Word and PDF files, so you can modify the text to suit your needs if you like.