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Blowin' in the Wind, Issue #049 Speed Velocity Acceleration and Meteorology - December 1, 2007
November 29, 2007
Hello ,

# Speed velocity acceleration and meteorology

How important are speed velocity acceleration and other physics concepts to meteorologists? They form the basis of our understanding, as we balance forces to come up with stable patterns in the atmosphere. Here is a simple example.

What happens when air blows across a uniform flat motionless surface? It goes straight. What happens when it blows across a moving surface? It may go straight and it may not. That depends on whether you (or your camera) is moving with the surface or not. An observer on a moving surface may see it go straight across, albeit at a different angle. An observer on a rotating surface will even see it curve.

# How so?

A mathematician named Gaspard-Gustave Coriolis gave us a way to calculate the effects when something moves across a spinning object. And since the earth spins, his formulas come in handy for making wind vector calculations on our world.

We call it the Coriolis effect. It describes the path of a straight-moving object as seen from someone on the rotating earth. All objects move tend to straight unless acted upon by some outside force. The person on earth will see the object curve to the right (or left in the Southern Hemisphere) and think it's being acted upon by a force. It's actually moving straight, though, and our earthbound observers (and mathematicians) use this imaginary Coriolis force to explain the change in direction. This force is very weak, depends on the objects mass and velocity and does not make much of a change in the objects path until it travels several kilometres. Therefore it is NOT the driver determining the direction of draining bathtubs as many say.

# And now some physics

The magnitude of the Coriolis force is proportional to both the mass and the speed of the object. That means if you double or triple the mass, the force doubles or triples as well. Same goes for its speed, if you do not change the direction (as the Coriolis force depends on the direction also.) If you understand some basic physics, you would also see that the acceleration caused by the Coriolis force does not depend on the mass of the object, but is still proportional to its speed. Remember, F = ma.

Look up Coriolis force on Wikipedia and you will see some simple demonstrations of the Coriolis effect.

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