A totally unexpected result was obtained with the silly
putty ball. Silly putty has the property that it stretches easily
when stretched slowly, it breaks when stretched quickly and
bounces when dropped on a surface. When the silly putty
ball was dropped on the piezo, it was discovered, with some
initial astonishment, that the piezo generated a negative output
signal commencing about 30 ms before the ball made
contact with the piezo, as shown in Fig. 4. No other ball had
this effect, and the effect was observed only with a freshly
prepared silly putty ball, created by stretching the putty and
rolling it into a ball. The effect was traced to electrostatic
charging of the ball to about 1 kV when it was stretched. The
effect was simulated by charging a plastic rod and moving it
toward or away from the piezo. The capacitance between the
ball and the piezo was only a few pF, but this was sufficient to generate a voltage of about 0.2 V across the piezo. The
ball was able to hold its charge for about 20 min, despite
repeated handling and dropping of the ball.
A totally unexpected result was obtained with the sillyputty ball. Silly putty has the property that it stretches easilywhen stretched slowly, it breaks when stretched quickly andbounces when dropped on a surface. When the silly puttyball was dropped on the piezo, it was discovered, with someinitial astonishment, that the piezo generated a negative outputsignal commencing about 30 ms before the ball madecontact with the piezo, as shown in Fig. 4. No other ball hadthis effect, and the effect was observed only with a freshlyprepared silly putty ball, created by stretching the putty androlling it into a ball. The effect was traced to electrostaticcharging of the ball to about 1 kV when it was stretched. Theeffect was simulated by charging a plastic rod and moving ittoward or away from the piezo. The capacitance between theball and the piezo was only a few pF, but this was sufficient to generate a voltage of about 0.2 V across the piezo. Theball was able to hold its charge for about 20 min, despiterepeated handling and dropping of the ball.
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