A ballistic or compound pendulum is used either to determine the velocity of a projectile or as a laboratory tool to teach impact momentum and principle of work and energy. It also lends itself well to the study of energy losses caused by the inelastic impact of a projectile with a medium. One useful application of the latter use of these pendulums is in the investigation of the effects of medium characteristics on the energy loss and the design of more effective lethal weapons.
A compound pendulum has been designed, instrumented and used to measure the energy losses during the plastic impact of a projectile with an arbitrary medium. The energy loss is calculated from the projectile velocity just before impact and the pendulum angular velocity immediately after impact or the pendulum maximum angular displacement. The angular displacement and velocity measurements are performed by a precision potentiometer and a PC-based data acquisition system in an automated manner to enable collection of extensive data in a reasonable period of time. The PC-based data acquisition used in this study is an in-house developed one that is capable of handling and storing massive amount of data and providing the ability to perform statistical and other computational analyses.
This paper discusses the procedure for designing the impact pendulum, in particular the selection of proper transducers and the data acquisitions system, and gives an overview of the software that has been developed to fully automate the energy loss calculation.