Demonstrating Density: Who Knew They Could Be So Dense?

by:  Tami O’Connor

Density is not typically an easy concept for most middle school students and even more difficult for younger students, but it doesn’t need to be.  We all know that D=m/V, but the easiest way I found to explain it to my students was to have them visualize a common dilemma in my home immediately preceding a vacation.  For years, as a poor starving teacher, I only had one suitcase, and it was actually a hand-me-down from my mother.  It was a medium sized Samsonite, hard cased piece of luggage.  When approaching the topic of density in my classroom, down from the attic it came.

My explanation began with an imaginary week-long summer vacation to a low-key resort.  The class and I would brainstorm the items I needed to pack for my trip.  Generally, the list included items such as a few bathing suits, shorts, t-shirts, a pair of flip flops, some PJs, underwear and a few toiletries.  It was obvious by looking at the size of my suitcase that in addition to my meager belongings, I could have probably also fit one of my students in my bag…  ok, perhaps one of the smaller kids.

I explained that when I closed the suitcase, it was hard to see, simply by looking at it, how heavy it was.  The lesson didn’t stop there.  We now planned my one-week ski vacation to Vermont during the February break.  Once again, my students and I made up my pack list.  The list included a couple of heavy sweaters, long johns, gloves, a hat, boots… as you can imagine, the list went on and on.  The question was, where to put it all.  Of course, since I had only one suitcase, the answer was easy. Read the rest of this entry »

Density of Gasses

by:  Tami O’Connor

Why do some objects float while others sink?  Archimedes discovered that an object is buoyed upward with a force equal to the weight of the fluid displaced.  An object will float in a fluid whenever its weight is less than the weight of the fluid displaced; otherwise it will sink…  So what does this mean in English??? An easier way to think about it is that an object that is less dense than the fluid it is in will rise to the top of the more dense fluid.

In demonstrations of liquids of varying densities, the liquid with the greatest density will sink to the bottom of the container while the less dense liquid will remain on the top.  There are wonderful demonstrations you can conduct with your class using immiscible liquids (liquids that do not mix) of different densities, and there are a number of high interest experiments your students can conduct using liquids of different densities.  If you find this topic interesting, please visit the blog we wrote on the W-Tube.

Gasses also have varying densities, but in the elementary and middle school classrooms, students don’t often have the same opportunity to work with gasses as they would liquids, or more often, liquids and solids. Read the rest of this entry »