An apparent force (→ inertial force) that acts only on moving objects in a rotating coordinate system. It was discovered by G. Coriolis in 1828. In a rotating system with angular velocity ω, the Coriolis force for an object of mass m moving at speed v has a magnitude of 2 m ω v sin θ and a direction perpendicular to the axis of rotation and the velocity vector. θ is the angle between the axis of rotation and the velocity vector. If a ball rolling on a smooth rotating plate appears to be moving in a straight line when viewed from the outside, it will move in a spiral motion in the opposite direction to the direction of rotation when viewed from the plate. This is because the Coriolis force acts in a coordinate system that rotates with the plate. Since the Earth is a rotating coordinate system that rotates on its axis, a Coriolis force acts diagonally upward to the south on a train traveling from west to east along a latitude line at a speed of 250 km/h, with a magnitude of about 1/1000 of gravity. The Coriolis force is small for small-scale movements, but its effect becomes apparent when it accumulates over a long period of time. In the Northern Hemisphere, the vortex of a typhoon rotates counterclockwise when viewed from above, and in all oceans, warm currents rotate in the same direction as the Kuroshio Current due to the effect of the Coriolis force (opposite direction in the Southern Hemisphere). In 1815, J.-B.-L. Foucault demonstrated the rotation of the Earth by performing an experiment in Paris in which the plane of oscillation of a long pendulum (→Foucault's pendulum) slowly rotates east, south, west, and north due to the Coriolis force. This is called the Foucault experiment. In the Southern Hemisphere, the direction of rotation of the plane of oscillation is reversed. Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information |
回転座標系において運動物体にだけ働く見かけの力 (→慣性力 ) 。 G.コリオリが 1828年に見出した。角速度ωの回転系では,速さ v で動く質量 m の物体に関し,コリオリの力は大きさ 2mωv sin θ で,方向は回転軸と速度ベクトルに垂直である。 θ は回転軸と速度ベクトルのなす角である。なめらかな回転板の上を転がる玉が外から見て直進するならば,板上に乗って見れば回転方向と逆回りに渦巻き運動する。これは板とともに回転する座標系ではコリオリの力が働くためである。地球は自転する回転座標系であるから,時速 250kmで緯度線に沿って西から東へ進む列車には重力の約1/1000の大きさで南へ斜め上向きのコリオリの力が働く。小規模の運動であればコリオリの力は小さいが,長時間にわたり積重なるとその効果が現れる。北半球では,台風の渦が上から見て反時計回りであり,どの大洋でも暖流が黒潮と同じ向きに回るのはコリオリの力の効果である (南半球では逆回り) 。 1815年 J.- B. -L.フーコーはパリにおいて,長い振り子 (→フーコーの振り子 ) の振動面がコリオリの力によって東,南,西,北の順にゆっくり回転することを実験して,地球の自転を実証した。これをフーコーの実験という。南半球では振動面の回転の向きが逆となる。
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