AP B Physics notes
Mr. Elia
Physics? - the study of how nature behaves
Mechanics - the study of how objects react when forces are applied to them
for example the simple act of pushing a toy car causes it to move...
The motion alone may be analyzed by observing items like speed, distance and time.
These items are inter-related, but ultimately the motion was caused by a force.
Kinematics is the study of motion alone without regard for the forces that caused that motion.
Length, mass, and time are three basic quantities fundamental to the study of mechanics.
SI system ( system internationale in french) begins in 1960 - the system of units we use for the
fundamental quantities in science.
SI units:
Length in meters, m
Mass in kilograms, kg
Time in seconds, s
the “m k s” system is a subgroup of the SI system
Length - the meter today is the distance traveled by light in 1/299792 seconds
previously it was defined as 1 ten millionth the distance from the equator to the north pole (1799)
Mass - the kilogram is based on a cylinder of a platinum-iridium alloy in Sevres France (a suburb
of Paris)
when the metric system was first devised it was one thousand cubic centimeters of pure water
Time - the second ... before 1960 it was based on a fraction of the solar day but now it is based
on a cesium-133 atomic clock
A dimension is a physical nature of a quantity like length, mass or time.
Dimensional analysis 1. Used to check if an equation is correct
for example. Is d = vt ?
m = m/s* s
L = L/T * T so L = L (Length = Length ) and it checks out
2. To derive a formula ex. - m/s represents speed so the formula for speed must be
Length/Time also known as d/t for distance over time
speed = d/t
Uncertainty in measurement
for  and  round the final answer to the least # of sigfigs of the numbers that went into the
calculation
ex. l = 16.3 cm, w = 4.5 cm and area = l X w = 16.3 cm x 4.5 cm = 73.35 cm2
rounded area = 73 cm2 to 2 sigfigs based on the number 4.5 cm
but, this is assuming we knew the length and width exaclty.
Realistically, we may only know each to a certain degree of precision.
Ex. 16.3  0.1 cm and 4.5  0.1 cm
therefore A = l x w = (16.3  0.1 cm) x (4.5  0.1 cm)
which could = as high as 16.4 cm x 4.6 cm = 75 cm2
or as low as 16.2 cm x 4.4 cm = 71 cm2
so A = 73  2 cm2
scientific notation resolves the ambiguous nature of writing numbers out
ex. If the number 1500g had 3 sigfigs make it 1.50 x 103g instead of 1500 with a dash over the
first zero
With + or - consider the least # of decimal places
ex. 123 + 5.35 is not  128.35 it is 128
ex. 1.0001 + 0.0003 = 1.0004
ex. 1.02 - .998 = 0.022 but rounded correctly is 0.02