Saturday, December 20, 2008

Coriolis Effect

The Coriolis Effect is the apparent deflection of a moving object when viewed from a rotating frame of reference. The effect is named after the French scientist who first described it in 1835. The effect is most commonly associated with the rotation of the Earth. Objects that travel in a straight path appear to veer right in the northern hemisphere and left in the southern hemisphere. In actuality the object stays on a straight path and only appears to curve due to our rotating due to our rotating frame of reference on the Earth.

The apparent force causing a Coriolis Effect is a fictitious force because the effect is only obtained in a rotating frame of reference. When visualized from the inertial frame of reference it is apparent that there is not actual force working on the object. However, despite the fictitious nature of the force, it can be describes in mathematical terms.

F= -2mΩ x v

Where: F is the Coriolis Force; m is the mass of the rotating object; v is the velocity of the particle; and Ω is the angular velocity vector of the rotating object.

Mathematically explaining the Coriolis Effect is important in order to make predictions on the observed path of objects on the Earth. Two common uses of the Coriolis Effect are in long range ballistics and meteorology.

Coriolis Effect on Ballistics

The Coriolis Effect has implications on long range ballistics, such as artillery shells. Due to the rotation of the Earth, the ballistic will appear to hit to the right of the target in the Northern Hemisphere. The ballistic itself is not curving but following a straight path. It is the rotation of the Earth that makes the ballistic miss.

An object that moves longitudinally along the Earth will appear to deflect to the right because of the eastward rotation of the Earth. In order to compensate for this deflection, the artillery round must be aimed to the left of the actual target in order to hit the target.

The principles of the Coriolis Effect are best exemplified on a smaller frame of reference. This animation of two figures passing a ball on a moving carousel demonstrates the principles of the Coriolis Effect as seen on Earth. When the one figure passes the ball from the center of the rotating carousel to the outside, the ball's trajectory will remain straight; however it will miss the recipient because of the rotation of the carousel. When both figures are on the outside of the carousel and pass the ball, the ball will travel straight but will appear to swerve in relation to the figures on the carousel.

Coriolis Effect on Meteorology

Air tends to flow from low pressure areas to high pressure areas. However, when we observe the actual flow of air masses notice a tendency to flow perpendicular to low pressure areas. This phenomenon can be explained by the Coriolis Effect. As the following video shows, we would predict the flow of air to go directly towards the low pressure zone. However, since the Earth is rotating, we observe an air flow perpendicular to the expected path. Meteorologists need to account for this effect when making weather forecasts.

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