Hooked on Science: Singing rod

You can make an aluminum rod sing with a few items from around the house.

Materials

* Aluminum rod

* Rosin

Instructions

STEP 1: Rub the rosin on your pointer finger and your thumb.

STEP 2: Pinch the rod with the other hand at exactly the middle point and hold the rod into the air.

STEP 3: Gently stroke the aluminum rod from the center to the end of the rod using your rosin-coated finger and thumb. Repeat and slightly increase the pressure of your stroking hand until you hear a high-pitched tone.

Explanation

When you hold the aluminum rod in the center and stroke it with rosin-coated fingers, your fingers slip and stick as they slide along the rod. This causes the rod to start moving with one of its natural frequencies of vibration -- a half-wave tone. As you continue to stroke the rod, the vibrations and the loudness increase. The node is a place on the object that is not moving. An anti-node is a place on the object with maximum vibration. Touching a node will not dampen the sound; touching an anti-node will.

Jason Lindsey is a science outreach educator with Hooked on Science. Check out his website www.hookedonscience.org for webcasts and experiments that might get you hooked on science. Send him your science questions at jlindseyhookedonscience.com.