The note played by the bar is said to have a long sustain . With time, the organized motion of the atoms of the rod which we hear as sound turns into the disorganized motion of thermal energy, warming the rod imperceptibly. Some energy goes into sound in the air. Different materials have different rates at which organized motion is turned into heat. Aluminum bars ring for a long time.
Steel bars ring for a shorter time and lead bars ring for a shorter time still.
Hold the bar in the center and tap it downward near the end. Notice that the lower note is louder than before. Even in this case, the lower note eventually goes away, and the high note remains. Hitting the bar straight into the end makes the bar vibrate along its length, the resulting vibrations are called longitudinal vibrations they make the high note that you hear. Do the following then do each of the activities below.