Using Blocks of Cheese to Teach the Concept of Density

MANY phenomena in this world make us wonder, How can it happen? Some of the common questions asked are:

(1) Why don't oil and water mix?
(2) How can a big and heavy ship float in the sea?

These questions were teasers for students before they got into a lesson on density. The questions were asked by Subroto, S.Pd, M.Pd, a Physics teacher of SMPN 1 Jatinom Klaten, when doing teaching practice at MTsN Klaten, with Nurhadi, a Science teacher from SMP 1 Tahunan Jepara.

To answer the questions and to understand more on the concept of the density, Pak Broto divided the class into six groups. To each group, he gave a worksheet, which told the students how to determine the density of a substance. The materials for the experiment were brought from home by the students. Each group had to find the density of two kinds of objects. The first kind of object had a defined shape and consisted of blocks of iron and cheese. The second type of object second did not have a defined shape and consisted of cooking oil, water and gravel. Each student in the group did their respective tasks. Some of them weighed, measured and some wrote down the data they had got from the observation. Pak Broto supervised the process and assisted them when necessary. The students were absorbed with their work and did it well. At the end, they had to prepare their presentations.

From the presentations, there were some interesting points to notice: (A) Objects made of the same substance, although of different sizes, have the same density. (B) Objects made of different substances, though having the same sizes and weight, have different densities. And from this data it was concluded that objects can be distinguished from each other by knowing the density of each substance. Students found out when oil and water are mixed, the oil floats above the water because of differences in density. Based on this the students were able to understand why a ship can float in water. Applause echoed in the classroom as a tribute to the best group in carrying out the experiment, the results and their presentation. A bell sounded to mark the end of the activities. Pak Broto did not forget to close the lesson "Ok class, time is up. Thanks for your attention. See you next time."