Fluid resistance to moving spheres

Abstract

In a previous paper on the resistance of air to falling spheres, attention was drawn to the value of supplementing that work by observations on the fall of solid spheres in liquids, and the present paper gives the results of such experiments. They confirm our previous conclusions as to the increased resistance to accelerated motion and they give more precise values for the resistance to uniform motion, a problem which can now be regarded as fairly solved on its experimental side. In these experiments, spheres of steel, bronze and lead, up to 5 cm. in diameter, were allowed to fall freely in water through distances up to 200 cm. The water was contained in a special steel tank, with two opposite faces of plate glass; its cross section was square, 45 cm. in breadth. Each ball was released from supporting rings beneath the surface of the water, and the measured fall ceased when it struck a small platform which could be set at any desired depth. At the instants of release and striking, a phonic chronograph (as previously described) was started and stopped by appropriate electrical devices, and the time of fall for a series of distances was then recorded for each ball.