1. Phys141 Principles of Physical Science Chapter 16 Place and Time
Instructor: Li Ma
Office: NBC 126
Phone: (713)
Webpage:
Department of Computer Science & Physics
Texas Southern University, Houston
Nov. 15, 2004

2. Topics To Be Discussed Cartesian Coordinates Latitude and Longitude
Time
Skip § §16.6

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. Meridians
Equator
Parallels

10. 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

11. 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

12. 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

13. 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

14. 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 times during a revolution, revolves 0.985° in a day

15. 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

16. 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

17. 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

18. 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

19. 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