Timing Falling Bodies

Time

Ships at Sea• Latitude – position North/South

equals the height of the North Star above the horizon 1/60 degree = one nautical mile

• Longitude – position East/WestThe stars rise in the east and set in thewest.

• At the equator you are going 1000 mph• To know your longitude you needed to know

the exact time.

Galileo

• In 1582, while praying in a church, Galileo observed the chandeliers swinging. He timed the swings against his own heartbeat.

• The period of the pendulum does not change with the size of the arcof the swing. (approximately)

U.S. Naval Observatory• Washington, DC• Today: Atomic Clocks• Vice President’s

Residence

Electricity

• Which side is positive?• The positive side alternates

60 times each second• Positive to negative and back

is one cycle• The period is 1/60 second• Oscillates 60 cycles/sec

The Philadelphia Electric Company Provides Electric Energy and Timing Signals