Transcript Time Dist Units

Definitions of Time
Newton: “I do not define time, space, place and
motion, as being well known to all”
Time (Merriam–Webster dictionary): A period
during which an action, process, or condition
exists or continues.
Period (Merriam–Webster dictionary): An
extent of time.
Definitions of Distance
Newton: “I do not define time, space, place and motion, as
being well known to all.”
Length (MW): a measured distance or dimension
Distance (MW): a measure of separation in space
Measure (MW): the dimensions . . . of something ascertained by
measuring
Dimension (MW): measurement of extension (as in length)
“God’s Coordinate System”
“Absolute, true, and mathematical time . . . flows
equably without regard to anything external; relative,
apparent, and common time is some sensible and
external measure of (time) by the means of motion,
which is commonly used instead of true time; such as
an hour, day”
“Absolute space . . without regard to anything external,
remains always similar and immovable. Relative
space is some movable dimension or measure of the
absolute spaces . . . Absolute and relative space, are
the same in figure and magnitude”
Evolution of the meter
1 meter = 1 ten–millionth of the distance from the
equator to the North Pole
Distance between scratches on a bar kept in Serves,
France
1,650,763.73 wavelengths of orange light from 86Kr.
One inch = 2.54 cm exactly
Evolution of the second
One second = 1/86,400 of a day
Amount of time it takes a pendulum one meter long to
swing from one side to the other
9, 192, 631, 770 transitions between the hyperfine levels
in 133Cs. (1967)
Means one 133Cs vibration is 109 ps (picoseconds)
Derived Quantities
Speed = distance ÷ time
Acceleration = speed ÷ time
Force = mass × acceleration (Newtons)
Energy = Force × distance
Speed of light is special
c = 3 × 108 m/s = 186,000 miles/sec
(measurement)
Define c ≡ 299, 792, 458 m/s exactly
One meter is distance light travels in
1/299,792,458 seconds ( = 3 ⅓ ns )
( = 30.66 133Cs vibrations).
Modern Definitions of Standards
1 second = 9, 192, 631, 770 transitions in 133Cs
Speed of light = 299, 792, 458 m/s ≈ 3 × 108 m/s.
1 kilgoram is the mass of a standard bar in France
1 meter = distance light moves in ≈ 3⅓ ns. (derived)
Other Things
We are very familiar with the idea of magnitude:
“How Much?”
Things like time and mass don’t have direction
associated with them: scalars
What about Direction?
Some quantities require more than just
magnitude in order to completely define
them.
Quantities with both magnitude and direction:
vectors.
Force is a vector
Complications
Distance is a scalar; Displacement is a vector.
Speed is a scalar; Velocity is a vector;
the
difference is very important. The magnitude of
velocity is speed.
Not so complicated
Acceleration, Force, Momentum, Angular
Momentum: Vectors!
Mass, Time, Energy, Power: Scalars!