Although the electrical charging of objects brought into contact has been observed for at least two thousand years, the details of the underlying mechanism are still not yet fully understood. The present paper deals with the very basic process of contact electrification between two metals. We have developed an experimental method to follow the charge of a small sphere bouncing on a grounded planar electrode on a time scale down to 1 µs. It reveals that the sphere is discharged in the moment of contact which lasts about 6-8 µs. However, at the very moment of disruption of the electrical contact it regains charge far beyond the expectation according to the contact potential difference. The excess charge rises with increasing contact area.

To study the motion and the contact electrification, gold spheres with 1 mm in diameter are dropped through a small orifice into a parallel plate capacitor. The spheres bounce on the lower plate which is virtually grounded by a charge amplifier measuring the induced as well as transferred charges. The self-built high bandwidth charge amplifier has a voltage gain of 12.06 and an input capacity (sum of setup + amplifiere input) of 21.4 pF. The output of the amplifier was recorded by Picoscope 5444D digital scope using a sampling rate of 31.25 MHz at a sensitivity of 20 mV. The CSV output of the PicoScope 6 software was used to store the data.

The datafile 20201211-0025.csv can be read by any standard software able to handle .csv data files. e.g.  Origin etc.

The first column gives the time in (ms), the second the signal in (mV). The dataset is large, with 31 million data points.