If you touch both metal contact points on the UFO ball at the same time you close the circuit inside the ball which causes the ball to light up and make an eerie alien sound. You can produce the same effect by touching one metal contact point and holding hands with someone else as they touch the other metal contact point. The principle of operation here is that the circuit of the ball has to be closed for it to work, just like the circuit of a light switch has to be closed for the light to turn on. Electricity flows through the electronic components of the ball only when the circuit is closed, and when this happens the electronic components turn on and create a dazzling display of light and sound.
Check out a video of a UFO ball:
The electricity used to power the ball is provided by batteries. The ball is designed so that the electricity must travel through an external path before turning on the ball (thus closing the circuit). The external path is provided by any conductor that touches both metal contact points on the ball.
This ball demonstrates that your body conducts electricity, just like a piece of metal does. What happens if you wear gloves and then touch both metal contact points on the ball? What happens if your hands are wet? How many people can join hands and still be able to turn on the UFO ball?
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