The Ice Dancer
Yup, as we saw at blind science, the `experts' don't really know what makes that Ice Dancer spin faster and faster as she straightens-up, bringing her limbs in, closer to her `axis of revolution'
But she can do it! - Watch any ice-dancer!
So those `experts' just say it's "Conservation of Angular Momentum"
[hoping no-one will ask "Why? - How?"]
A less elegant example is - "swing a brick on a string and then shorten the string by putting a tree in the way"
The brick suddenly accelerates!
[if U try it - maybe use a plastic brick]
Well, we're going to check the phenomenon.
And, hopefully, find its secrets.
First let's look at the Earth.
You know the Earth rotates once in 24 hours.
As it's about 24,000 miles (38,000km) around the equator, that means everything near the equator is moving eastwards quite speedily: at approximately 1,000 mph (1600km/h).
But away to north or south, in cooler climes, things move east at around half that speed - maybe only 500 mph or so (800km/h).
And closer - within spitting distance say - to the Poles, surroundings are moving east at maybe only 1 mph (1.6 km/h).
remember from `inertmass' that objects don't easily move, or stop if they're already moving?
It's always known as inertia if not moving, & sometimes called momentum if moving, but it's the same phenomenon
objects tend to carry on doing what they were doing
That means: pick up a rock at the equator (1,000 mph) and throw it northward [inwards] to a cooler region which only moves east at 500 mph - when the rock arrives it'll be moving at an extra 500 mph eastwards!
[disregarding all kinds of losses - and the fact that nobody's that strong]
So the rock has apparently accelerated eastwards with respect to Earth's spin at that point.
And obviously if you did the opposite: picked up a rock, in Scotland say, and threw it southward [outwards] to the equator - when it arrived it'd be moving westwards at around 500 mph.
So that rock would appear to have decelerated w.r.t. Earth's spin at the equator.
However, in reality - they'd both simply be doing what they were already doing.
[all those apparent moves are in opposite direction in the Southern hemisphere]
Yes - it's the Ice Dancer phenomenon all over again - but Earth-sized this time.
[ move inwards to speed up - outwards to slow down ]
So how does all that affect the winds?
Well, you know a "low" means bad weather - but it also means rising air - 'cos that low pressure allows surrounding air masses to push in. Evenly?
Well, no! It doesn't happen like that theoretical picture above.
In reality, you know that anything going NORTH must also be moving eastwards and anything going SOUTH must also be moving westwards.
[IN NORTHERN HEMISPHERE - OPPOSITE IN SOUTHERN HEMISPHERE]
Here's what really starts to happen whenever there's even a small `low'.
So a rotating wind-system very soon develops around a `low', and the deeper the `low' the faster the winds will rotate, 'cos masses of air are pushing in faster from surrounding areas.
Hey! - don't forget, it'll rotate opposite way in Southern hemisphere.
However, in the wide oceans the effect can build up into huge dynamos of swirling wind and sea. There's a big one below
[guess it's in northern hemisphere - spinning anti-clockwise]
Again - below, here's a rare cyclone in S Atlantic, unofficially called Hurricane Catarina - seen here by coast of Brazil
[check that clock-wise spin]
All storms:- hurricanes or typhoons (low pressure) or Anti-Cyclones (high pressure) begin with that first clockwise or anti-clockwise swing - due entirely to "Coriolis".
This is the biggest Anti-Cyclone we know of.
CLICK for HOMEPAGE
|Applied to wind, weather and various projectiles, this phenomenon was formally named for Gaspard Gustave de Coriolis who discovered the effect - in 1835|
Did you read about
Well, they're on show in some big cities, and they're really only heavy-weight, long-suspension, free-hanging pendulums.
And here's a clue - the farther one is from the equator - the more it appears to try to swing in a complete circle in one day.
In fact - if you hung one at the North or South Pole - it would complete a daily circle with its swings.
Here's one working
It's on the Foucault Pendulum pages of the University of Guelph, Ontario, Canada.
How do they work? What powers their apparent turning - against the spin of the Earth?
Yes, at the North Pole one would appear to turn clock-wise and at the South Pole it would appear to rotate anti-clock.
Here's a step-by-step
Yes - it's the same phenomenon we've been checking for the Ice Dancer, for bathtubs, for thrown rocks and for winds & storms.
Reaction of mass held in rotation, or released:
"Centripetal or Centrifugal Force"
Reaction of mass to varying radius of rotation:
"Conservation of Angular Momentum"
Reaction of mass to varying angles of rotation:
Reactions of mass to other movements:
|The apparent `acceleration' (positive or negative remember?) of the moving body can be approximately calculated by:
2 Å V sin þ
Where Å is the angular magnitude of the angular velocity of rotation of the Earth, V is the speed of the body relative to the Earth's surface, and þ is the latitude.
(courtesy of `Larouse Dictionary of Science and Technology')