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Mathematical expressions have been constructed that allow the large-scale global convection characteristics of the high-latitude ionosphere to be reproduced. The model contains no discontinuities in the ion convection velocity and as such should be useful in F region chemical models. The number of variables in the model allow such features as the dayside throat and the Harang discontinuity to be modeled. The applicability of the model to magnetospheric physics is limited by the exclusion of largemagnitude small-scale flow features associated with discrete arcs and by the inability of the model to produce separate flow cells at the same local time.

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Two samples of nominally identical material will usually charge each other if they are rubbed together asymmetrically, e.g. in such a way that a small region of one rubs across a large region of the other. It has previously been supposed that the asymmetric rubbing induces some physical difference, in particular a temperature difference, between surfaces, which in turn causes charge transfer. However, experiments on polymers (reported in the preceding paper) are not easily reconciled with this explanation. In this paper we show that it is not necessary to invoke any physical distinction between the two insulators to explain charge transfer. Certain electron distributions can result in net charge transfer during asymmetric rubbing even though the temperature (and other physical properties) remains exactly the same for the two surfaces. We present a quantitative model and we show that it is capable of explaining a wide range of experimental facts about charge transfer between identical insulators.

A mechanism is proposed for the transfer of charge from a metal to a polymer which leads to a natural explanation of the (previously unexplained) linear relationship between the charge density and the metal work-function. In the simplest case of a single non-sliding contact it is found that the charge density does not depend on the metal. But if the contact is repeated many times, or if the metal slides on the plastic, the final charge density varies linearly with the metal work-function. In a single (non-sliding) contact electrons are believed to tunnel from the metal into trapping levels a short distance from the interface; thermodynamic equilibrium is not achieved because the difference in electrostatic potential across this thin layer of charge is not sufficient to raise the energy of the trapping levels up to the Fermi energy of the metal. But repeated contacts (or sliding contacts) transfer charge to greater depths and make equilibrium possible. This hypothesis predicts an equilibrium charge density linearly dependent on the metal work-function.

The author has measured the electrostatic charging of two metal bodies which have been brought into contact and then separated. The charge Q is found to be given by Q=C0Vc, where Vc is the contact potential difference and C0 is the 'contact capacitance'. A technique for measuring C0 is described, and it is shown that C0 is simply related to the height of surface asperities. The charge is not affected by the velocity of separation or by sliding during separation in contrast to the findings of previous investigations. Tunnelling of electrons during the initial stages of separation does not appreciably reduce the final charge.

No abstract

Nominally identical samples of the same material frequently charge each other when they are rubbed together. It has previously been supposed that the charge transfer is associated with the temperature difference (due to frictional heating) which results when one sample slides over the other. We find that charge transfer is not influenced by sliding speed and we conclude that it cannot be the result of a temperature difference. On the other hand. charge transfer is strongly affected by the preparative treatment of the surface, and in particular seems to be associated with surface damage. The results presented in this paper form a general description of the phenomenon. Any theoretical model must account for these observations: in the following paper we develop such a model.