EARTH’S ROTATIONEARTH’S ROTATION

CHAPTER 4.2CHAPTER 4.2

ObjectivesObjectives

Give evidence of Earth’s rotation.Give evidence of Earth’s rotation. Relate Earth’s rotation to the Relate Earth’s rotation to the

day-night cycle and the time day-night cycle and the time zones.zones.

22

LIKE US TODAY,

EARLY OBSERVERS , WATHCHED THE SUNRISE IN THE EAST

AND SET IN THE WEST

EVIDENCE FOR EVIDENCE FOR ROTATIONROTATION PENDULUM, 1851 PENDULUM, 1851

JEAN FOCAULT NO JEAN FOCAULT NO FORCE ON SWING, FORCE ON SWING,

NO NO DIRECTIONAL CHANGE = EARTH CHANGE = EARTH TURNING BENEATH TURNING BENEATH PENDULUMPENDULUM

CORIOLIS EFFECT – CORIOLIS EFFECT – WIND DIRECTIONAL WIND DIRECTIONAL CHANGECHANGE

EVIDENCE FOR EVIDENCE FOR ROTATIONROTATION

CORIOLIS EFFECT – CORIOLIS EFFECT – WIND DIRECTIONAL WIND DIRECTIONAL CHANGECHANGE

RIGHT IN THE RIGHT IN THE NORTHNORTH

AND LEFT IN SOUTHAND LEFT IN SOUTH

Examine evidence of Earth turning about an axis

AXIS AND RATE OF AXIS AND RATE OF ROTATIONROTATION

ROTATION – COUNTERCLOCKWISE SPIN OF THE EARTH ABOUT IT’S AXIS.

TILTED 23.50 FROM PERPENDICULAR

1 ROTATION = 24 HR = 1 DAY

3600 / 24HR = 150 PER HOUR

10 / 4 MIN

AXISAXIS

RATE OF ROTATIONRATE OF ROTATION

LOCATION CIRCUMFERENCE ROTATIONAL RATE

POLES 0 MILES 0 MI/HR 420 NORTH 18,720 MI 780 MI/HR

EQUATOR 24,044 MI 1002

MI/HR

EFFECTS OF ROTATIONEFFECTS OF ROTATION

DAILY CHANGE DAILY CHANGE DAY TO NIGHTDAY TO NIGHT

SUN APPEARS TO SUN APPEARS TO RISE IN EAST RISE IN EAST AND SET IN AND SET IN WESTWEST

PENDULUM AND PENDULUM AND CORIOLISCORIOLIS

Day and Night VideoVideo

MEASURING TIMEMEASURING TIME

USED THE SUNUSED THE SUN RISE IN EAST SET IN WESTRISE IN EAST SET IN WEST EARTH ROTATES COUNTERCLOCKWISE WHEN EARTH ROTATES COUNTERCLOCKWISE WHEN

VIEWED FROM ABOVE NORTHPOLEVIEWED FROM ABOVE NORTHPOLE SUN MOVES IN AN ARC IN THE SKYSUN MOVES IN AN ARC IN THE SKY HIGHEST POINT IN ARC = SOLAR NOON = SUN HIGHEST POINT IN ARC = SOLAR NOON = SUN

DIRECTLY OVERHEAD TO AN OBSERVERDIRECTLY OVERHEAD TO AN OBSERVER– BECAUSE EARTH ROTATES, SOLAR NOON DOES BECAUSE EARTH ROTATES, SOLAR NOON DOES

NOT OCCUR AT THE SAME TIME DAILY NOT OCCUR AT THE SAME TIME DAILY – EX. PHILLY 75EX. PHILLY 7500 W AND DUBOIS 78 W AND DUBOIS 780 0 WW

ALTITUDE OF

SUN

HORIZON

EAST WEST

SOLAR NOON

Explore a model of Earth's daily rotation.

STANDARD TIME STANDARD TIME ZONESZONES TIME MERIDIAN – EACH 150 FROM

THE PRIME MERIDIAN. CENTER LINE OF A TIME MERIDIAN 7 1/2O.

EACH TIME MERIDIAN (150) IS 1 HR DIFFERENCE IN TIME

EARTH ROTATES 3600 IN 24 HRS 3600/ 24 HOURS = 150 PER HOUR THEREFORE EACH TIME ZONE IS 150 OF LONGITUDE

The prime meridian

SUNLIGHT

A time meridian

A standard time zone is 15° wide.

RULES FOR TIME ZONES

EAST – ADD TIME

WEST – SUBTRACT TIME

iF THE TIME IN DUBOIS IS 1:00 PM, WHAT IS THE TIME IN:

LA, DETROIT AND DENVER?

US TIME ZONESUS TIME ZONES

EASTERN (75EASTERN (7500 W) W)

CENTRAL (90CENTRAL (9000 W) -1 W) -1

MOUNTAIN (105MOUNTAIN (10500 W) -2 W) -2

PACIFIC (120PACIFIC (12000 W) – 3 W) – 3

INTERNATIONAL DATELINE IDL – 1800 MERIDIAN

– OPPOSITE THE PRIME MERIDIAN WHEN TRAVELING:

– EAST ACROSS DATELINE – SUBTRACT A DAY

– WEST ACROSS DATELINE – ADD A DAY

only at midnight on the international dateline does earth have the same day!

How dateline works

Traveling Across Time Zones