August 13, 2010
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 »
April 29, 2010
by: Allison A. Bailes III, PhD
A great new tool for home performance diagnostic testing has come onto the market – The Wizard Stick. It’s basically a small, hand-held theatrical fog machine that uses the same non-toxic fluid as its larger, more prolific brethren.
For the home energy auditor or the home performance contractor, this device provides an effective way to find air leaks and a compelling way to demonstrate them to homeowners. With a Blower Door depressurizing the home, you can walk around with the Wizard Stick, pull the trigger, and watch to see if the smoke just hovers near where it’s released or is blown away by air being pushed into the house through a leak.
It makes a nice stream of smoke and produces it quickly when you pull the trigger. Although it doesn’t have the neutral buoyancy that chemical smoke puffers have, I haven’t noticed that it’s far enough away from neutral to be a problem for home energy auditors. And of course, it has the big advantage of not being toxic. The common chemical smoke puffers available use titanium tetrachloride, which is very corrosive. Several years ago, I kept one of these in a metal locker, and even though it was in a plastic bottle inside a plastic bag, the inside of that locker showed significant corrosion after a short time. I’m happy to find a non-toxic smoke device that works. Read the rest of this entry »