Coriolis Effect - explain why

[alant]

I have just been trying to explain this to someone, that the wind from the North Pole high pressure, initially blowing south, gets redirected west (or right) away from the direction of earth spin by this effect.

No effect at the equator.

They replied, that if you spin a bowl of water quickly, the water will eventually spin in the same direction as the bowl, also if a foodmixer can turn liquid in a bowl the same direction as the beater, why does the the wind near the poles not also do this?

 

[AliM]

That is not the origin of the coriolis effect. The best illustration that makes sense to me is to think about an ant walking radially out from the centre of a record turntable. If the turntable is at rest, its path is straight out along the radius. If it's turning, the ant will follow a spiral track because it's being pushed sideways by the record's rotation and the further it goes, the further sideways it it pushed. At the equator, the ant (on a sphere now) is not moving radially, so there's no effect.

The air in the atmosphere follows the rotation of the earth near the surface, and further up, but its viscosity is quite low and its motion is dominated by pressure and temperature changes. However if a pressure change starts it moving North-south or vice versa, it will also be affected by the Coriolis effect and it will start to move sideways with respect to the earth.

Clear as mud??

 

[CaptainBob]

The flow of air is north to south, but the earth spinning beneath it makes it appear, relative to the observer, to be moving also more and more toward to the west as it gets further and further from the pole. Viscosity however will result in the air at the very surface not apprantly moving west (as your friends suggest, dragged along with the earth's surface) and this effect will progress upwards through the atmoshphere giving a gradient of how great the coriolis effect actually is at any altitude.

This is a guess.

 

[wotayottie]

The circumference of the earth is approx 21600 miles so the speed of rotation on the equator is 900 mph. The speed of rotation at the pole is zero and between pole and equator sped builds form zero to 900.

So relative to the surface of the earth a wind which is heading dead south from the pole will appear to be moving west . It wont do that at 900 mph or anything like cos friction at the surface will drage the wind along with it. Nevertheless, the rotation of the earth will give a westerly component to a wind heading south from the N pole.

 

[huzar30]

To put another way - the air at the equator is moving at the speed of the earth at the equator - around 500m/s. If this air moves north, it keeps its speed. However, the earth at 60°N is moving at only half this speed. Thus the air is now moving faster than the ground, and so will move to the east relative to the ground.

 

[Cornishman]

I have just been trying to explain this to someone, that the wind from the North Pole high pressure, initially blowing south, gets redirected west (or right) away from the direction of earth spin by this effect.

No effect at the equator.

They replied, that if you spin a bowl of water quickly, the water will eventually spin in the same direction as the bowl, also if a foodmixer can turn liquid in a bowl the same direction as the beater, why does the the wind near the poles not also do this?

There are several good videos on You Tube explaining this

 

[alant]

The circumference of the earth is approx 21600 miles so the speed of rotation on the equator is 900 mph. The speed of rotation at the pole is zero and between pole and equator sped builds form zero to 900.

So relative to the surface of the earth a wind which is heading dead south from the pole will appear to be moving west . It wont do that at 900 mph or anything like cos friction at the surface will drage the wind along with it. Nevertheless, the rotation of the earth will give a westerly component to a wind heading south from the N pole.

Both your explaination & Huzar30's make more sense than rolling balls for some reason, ta!