The Effect of Rotation: Foucault's pendulum

To demonstrate Earth’s rotation, the French scientist Jean-Bernard-Léon Foucault conducted an experiment in Paris in 1851. Using a steel wire 220 feet long, he suspended a 62-pound iron ball from the dome of the Panthéon and set it in motion, rocking back and forth. To mark its progress he attached a stylus to the ball and placed a ring of damp

sand on the floor below.

Source: http://physics.nad.ru/Physics/English/top_ref.htm#fouc01

At the latitude of Paris, the pendulum's path would complete a full clockwise rotation every 30 hours; on the Southern Hemisphere it would rotate counter-clockwise, and on the Equator it wouldn't revolve at all. At the South Pole, as the modern-day scientists confirmed, the period of rotation is 24 hours.

The audience watched in awe as the pendulum inexplicably appeared to rotate, leaving a slightly different trace with each swing. Actually it was the floor of the Panthéon that was slowly moving, and Foucault had shown, more convincingly than ever, that the earth indeed revolves on its axis.

P-waves propagate through alternate

compressions and dilations, so that the particle motion is in the direction of wave propagation.

Direction of wave propagation

Direction of wave propagation

S-waves propagate through shearing,on the other hand, with particle motionperpen-dicularto wavepropa-gation.

          

Source:

http://www.physics.orst.edu/~mcintyre/coriolis/North_Pole_GIF.html

Because of the Earth’s spin, surface wind traveling from pole to the equator blows increasingly to the west, against the direction of spin, as itapproachesthe equator. This is Corioliseffect. Equatorial surface wind thus flows to the west.

Coriolis effect:A hockey puck launched north from Equatorial Africa would follow the prime meridian on a stationary earth andarrive in London. On a rotating earth the inertial great circle path of the puck takes it to the east of the prime meridian, which the earthbound observer attributes to the rightward Coriolis force. The puck also ends up south of the target due to the centrifugal force.Source: http://www.physics.orst.edu/~mcintyre/coriolis/North_Lon_GIF.html

Risin

g A

ir(L

ow

pressu

re)

Ris

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Air

(L

ow

P

ress

ure

)

Sinking Air (High Pressure)

Sinking Air (High Pressure)

Ignoring rotation ... Equator receives

more solar heat than the poles.

Gravity at the poles is greater than gravity at equator.

Warm air rises above the equator, therefore, and cold air sinks at the poles, so creating the cells that Hadley had first proposed.

How the Hadley cells are created.

Hadley cells

n The 23½° tilt of Earth’s spin axis means that the two poles do not get the same amount of solar heat at the same time.

n North pole is tilted toward the sun from about March 22 to about Sept 22, when south pole tilts away from the Sun.

n Northern hemisphere thus has its longest day (or summer solistice) around June 22, and the shortest day (or winter solistice) around Dec 22, whereas the opposite occurs in the southern hemisphere.

n Seasons typically characterize the temperate latitudes (23½°– 66½° N and S), therefore, whereas tropics receive Sunlight all year round.

Source: http://vortex.plymouth.edu/sun/sun3d.html

Why do we have seasons?Northern

hemi-sphere

March 21June 22Sept 22Dec 22

Vernal equinoxSummer solistice

Autumnal equinoxWinter solistice

Southern hemi-

sphere

March 21Dec 22

Sept 22June 22

Question:

What if the Earth’s spin axis had no tilt?

•NASA’s Earth’s Seasons

http://www.sfgate.com/getoutside/1996/jun/tides.html

n Spring tides occur during Full Moon and New Moon, when Sun, Moon and Earth are aligned together.

n Neap tides occur during Moon’s first and third quarters, when lunar and solar gravity pulls are mutually perpendicular.

New Moon

Full Moon

1st Quarter

3rd Quarter

Mean absolute sea surface height estimated from 5 years of TOPEX/POSEIDON data rela-tive to the EGM-96 geoid.

Source: http://puddle.mit.edu/~detlef/altimetry/altimetry.html

Hurricane KatrinaLandfall on Aug 29, 2005Devastated New Orleans

Source:http://www.ncdc.noaa.gov/img/climate/research/2005/katrina/katrina-satellite.gif

The Dec 2004 Indian Ocean tsunam

i was produced by perhaps the strongest earthquake of the past 100 years. It occurred in the Java trench, off Bandar Aceh in north-western Sum

atra.This image is a work

of the National Oceanic and Atm

ospheric Administration

Seismicity at the Filled Trench offers the most likely scenario of the western U.S. facing the kind of disaster that the Dec 2004 Asian tsunami, caused by the magnitude 9+ Sumatra earthquake of Dec 26, 2004, wrecked on the Indian

Ocean coasts.

Box 2-3 (A) Water exists in solid, liquid and gas from only on earth

Box 2-3 (B) Hydrological cycle

B

Figure 2-9 Difference of heating over land and oceans

Figure 2-10 Sensitivity of solar heating to land vs. ocean

million years ago

Source: http://www.uwgb.edu/dutchs/EnvSC102Notes/102HowEarthWorks.ppt

The configuration of continents and oceans through these past

750 Ma

Pole-to-equator heating imbalances

Figure 2-11 Convection of heat

0°

90°S

60°S

60°N

30°S

30°N

90°N

                                                                      

                          

The relationship between the masses of the Earth, moon and sun and their distances to each other play a critical role in affecting the Earth's tides. Although the sun is 27 million times more massive than the moon, it is 390 times further away from the Earth than the moon. Tidal generating forces vary inversely as the cube of the distance from the tide-generating object. This means that the sun’s tidal generating force is reduced by 3903 (about 59 million times) compared to the tide-generating force of the moon. Therefore, the sun’s tide-generating force is about half that of the moon, and the moon is the dominant force affecting the Earth’s tides.