A ballistic pendulum was an apparatus formerly employed for ascertaining the velocity of military projectiles, and consequently the force of fired gunpowder. A piece of ordnance was fired against bags of sand supported in a strong case or frame suspended so as to swing like a pendulum. The arc through which it vibrated was shown by an index, and the amount of vibration formed a measure of the force or velocity of the ball. Research Ballistic Pendulum
 
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