Phys141 Principles of Physical Science Chapter 16 Place and Time Instructor: Li Ma Office: NBC 126 Phone: (713) 313-7028 Email: malx@tsu.edu Webpage: http://itscience.tsu.edu/ma Department of Computer Science & Physics Texas Southern University, Houston Nov. 15, 2004

Topics To Be Discussed Cartesian Coordinates Latitude and Longitude Time Skip §16.4 - §16.6

The Concept of Place and Time In physical science we observe and examine events in our environment Events occur at different places and at different times, so they are separated in place and time Space and time are related – Albert Einstein Place – location of an object Time – reference to periodic changes

Cartesian Coordinates The location of an object in our environment requires a reference system with one or more dimensions 1-D: one number line, the Celsius temperature scale 2-D: two number lines, perpendicular to each other, the point of intersection is assigned as the origin

Cartesian Coordinates (cont) The 2-D reference system is known as Cartesian coordinate system or rectangular coordinate system x-axis: the horizontal line y-axis: the vertical line Every position or point in the plane is assigned a pair of coordinates (x,y) The x and y coordinates give the distances from the y and x axes

Latitude and Longitude Any position on a rectangular plane can be located using Cartesian coordinate system We can also determine the location of any position on the spherical surface using two reference circles They are analogous to the Cartesian coordinate axes Latitude and longitude on the surface of the Earth

Latitude and Longitude (cont) A coordinate system known as latitude and longitude can be used to determine the location of an object on the spherical surface of the Earth Equator: an imaginary line circling the Earth at the surface, halfway between the north and south geographic poles The equator is a great circle

Latitude and Longitude (cont) Parallels: imaginary circles drawn around the Earth parallel to the equator Parallels are not great circle Meridians: imaginary lines drawn along the surface of the Earth running from the north geographic pole, perpendicular to the equator, to the south geographic pole A meridian is half of a great circle

Meridians Equator Parallels

Latitude and Longitude (cont) The latitude of a surface is defined as the angular measurement in degree north or south of the equator The latitude angular is measured from the center of the Earth relative to the equator The latitude angular is measured along a meridian Parallels are lines of equal latitude Equator 0°, the North pole 90°N, the South pole 90°S

Latitude and Longitude (cont) The longitude is defined as the angular measurement in degree east or west of the reference meridian This reference meridian is called Greenwich, or prime meridian 0° at Greenwich meridian (minimum value), 180° east and west are the maximum values The pair of latitude and longitude can determine the location on the Earth’s surface

Latitude and Longitude (cont) Parallels become smaller as the distance from the equator becomes greater The meridians are half circles, portions of a great circle Most maps are drawn with north at the top, south at the bottom, east at the right, and west at the left

Time The second is the standard unit of time For everyday purposes, the day is an important unit of time The day has been defined in two basic ways: The solar day is the elapsed time between two successive crossings of the same meridian by the Sun

Time (cont) The sidereal day is the elapsed time between two successive crossings of the same meridian by a star other than the Sun Because the Sun is much closer to the Earth than other stars, the solar day is longer than the sidereal day by about 4 minutes The Earth rotates 365.25 times during a revolution, revolves 0.985° in a day

Time (cont) Different local solar time is defined according to the position of the Sun 12 noon (local solar time) is the time when the Sun is on this meridian Ante meridian (A.M.): the hours before noon Post meridian (P.M.): the hours after noon

Time Zone Standard time zones: this scheme theoretically divides the surface of the Earth into 24 time zones, each containing 15° of longitude or 1 hour The first zone begins at the prime meridian All places within a zone have the same time, which is the time of the central meridian of that zone

Time Zone (cont) International Date Line (IDL): Traveling west into a different zone, you will “save an hour” – need to move the hour hand of your watch back 1 hour Traveling east into a different zone, you will “lose an hour” – need to set the hour hand of your watch ahead 1 hour International Date Line (IDL): was established at the 180° meridian

Time Zone (cont) When one crosses the IDL traveling west-ward, the date is advanced to the next day When one crosses the IDL traveling east-ward, one day is subtracted from the present date Practical problem regarding to time zones: find the time and date in a distant city when knowing your local standard time and date

Assignment Homework Assignment Reading Assignment Review Questions (page 433 – 434): 1,6,14,17,18,24,25,29,30 Exercises (page 435): 2,4 It’s due Monday, 11/29/04 Reading Assignment Chapter 17