## New Demos: Buoyancy and Electromagnetic Forces

We have introduced several new demonstrations recently, in a variety of topic areas. Be sure you take some time to visit our website occasionally and see what's new! Here are brief introductions to two of them.

Electricity and Magnetism: Forces Between Current-Carrying Coils

Check out K1-07 Interacting Coils, developed by student (now alumna) Sarah Monk! This is a new way of illustrating the forces between parallel current-carrying coils. This attractive new tabletop demonstration will be easier to use in many classes. Challenge your students to predict how changing the direction of the current will change the motion of the coil.

This demonstration was itself developed in conjunction with classwork, as part of a final project for PHYS411 last semester. There are many different ways to explore incorporating demonstrations and hands-on learning activities into your classes – not only using demonstrations to illustrate concepts, but advanced students can learn a great deal by developing systems and devices themselves!

Buoyancy, Density, and Pressure

At the suggestion of Mark Eichenlaub, we have also added F2-27 Buoyancy Paradox: Two Spheres. Two identical beakers of water sit on the pans of a pan balance. In one, a ping-pong ball is tethered to the bottom of the beaker so the ball floats submerged in the water. In the other, a steel ball if the same size hangs from an overhead hook, submerged at the same height. Invite your students to predict whether the pans will remain balanced, or will show one as heavier!

This demonstration was first developed for use in a presentation for AAPT's US Physics Team. Every year AAPT trains high school students for the International Physics Olympiad, and UMD Physics hosts their training camp in the early summer, with demonstrations and problem solving exercises.

Physics demonstrations can enhance learning and student engagement in a wide variety of contexts. What experiments could you use to expand student interaction in your classes?