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New experiments on the resistance experienced by fish in moving through water
776
CURRENT
TOPICS.
[J. I;. I.
New Experiments on the Resistance Experienced by Fish in Moving through Water. A. MAGNAN AND A. SAINTE-LAGUE. Rendus, Nov. 12, 1929.) In order to avoid the disturbing (Comptes effect of.an arm or cord attached to the fish a method was devised in which all exterior connection was absent. Immediately after the death of the fish it was weighed and its buoyancy determined. Lead was placed in its mouth to make it sink head downward in water. When released it moved downward through the water without appreciable oscillation. Through a network of reference lines a moving picture of the descending fish was taken and also of a swinging pendulum to furnish time data. Twenty-two varieties of fish were thus studied. In nearly all cases the distance fallen through was quite accurately proportional to the square of the time of the fall, as is the case with a body falling freely in a vacuum. Hence, just as the falling body has a constant acceleration, so also does the descending fish. The constant acceleration indicates the action of a constant resultant force. This resultant is in quantity the excess of the weight of the fish with the added lead over the upward force due to immersion in water augmented by the force opposing the motion of the fish. Since the first two of the mentioned forces are constant and since the resultant also is constant the opposing force too is constant. This holds up to velocities of descent of 2 meters per sec. The mackerel is a fish for which the resistance is constant but for the skate the resistance increases G. F. S. with the velocity, as is the case with a falling sphere.
CURRENT
TOPICS.
[J. I;. I.
New Experiments on the Resistance Experienced by Fish in Moving through Water. A. MAGNAN AND A. SAINTE-LAGUE. Rendus, Nov. 12, 1929.) In order to avoid the disturbing (Comptes effect of.an arm or cord attached to the fish a method was devised in which all exterior connection was absent. Immediately after the death of the fish it was weighed and its buoyancy determined. Lead was placed in its mouth to make it sink head downward in water. When released it moved downward through the water without appreciable oscillation. Through a network of reference lines a moving picture of the descending fish was taken and also of a swinging pendulum to furnish time data. Twenty-two varieties of fish were thus studied. In nearly all cases the distance fallen through was quite accurately proportional to the square of the time of the fall, as is the case with a body falling freely in a vacuum. Hence, just as the falling body has a constant acceleration, so also does the descending fish. The constant acceleration indicates the action of a constant resultant force. This resultant is in quantity the excess of the weight of the fish with the added lead over the upward force due to immersion in water augmented by the force opposing the motion of the fish. Since the first two of the mentioned forces are constant and since the resultant also is constant the opposing force too is constant. This holds up to velocities of descent of 2 meters per sec. The mackerel is a fish for which the resistance is constant but for the skate the resistance increases G. F. S. with the velocity, as is the case with a falling sphere.