An electrical method for the study of impact applied to the struck string

In the study of impact the time during which the two bodies are in contact and the pressure variations during that time are of considerable importance. For the experimental determination of the duration of the impact the electrical method introduced by Pouillet is usually used. This consists in allowing an electrical circuit to be completed by the contact between the two impinging bodies, and in measuring the total quantity of electricity which passes through the circuit, by means of a ballistic galvanometer, during the impact. An essential part of the calculation is the assumption that the electrical resistance of the circuit is constant, and in order to justify this assumption a large non-inductive resistance is usually included in the circuit. It is then supposed that the variation in the electrical resistance of the contact, due to the variation in mechanical pressure which is known to be present, may be neglected. The main feature of the experimental method used in the present research is that here a Duddell oscillograph has been substituted for the ballistic galvanometer used in the researches of previous workers. By this means advantage is taken of the variation in electrical resistance to obtain information about the corresponding variation in mechanical pressure.