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This experience shows how the charging and discharging electrostatic processes in a small metalic ball originate an oscillatory movement of the ball which moves as a pendulum
The device consists on two aluminium refreshment cans joined at the top by a fixed insulating bar in each end to one of the cans. A small metalic ball hangs from the bar suspended by a fine thread
The small ball is formed by folding foil
The part of the can surface where the small ball will collide is polished to promote the charging and discharging processes
The cans are connected to the terminals of a power supply
When the power is switched on, one of the cans becomes positively charged and the other negatively charged, and an uniform electric field is established between the two cans
Within the electric field, an electric charge distribution is originated on the ball surface and it behaves like an electric dipole
The side closest to the positive polarity can becomes negatively charged, and the opposite side becomes positively charged
The electrical atraction force between charges of opposite sign, given by Coulomb's law, causes a displacement of the ball toward the positively charged can. When it collides with the can, the ball becomes positevely charged and it is repelled, starting its movement in the opposite direction, toward the negatively charged can
Then, the small ball collides with the negatively charged can, becoming negatively charged, and it is again repelled and driven back to the opposite side
The process is repeated, resulting in an oscillatory movement of the ball colliding between both cans
This movement can be aproximately described as a simple pendulum movement
and it will remain while the electric field exists