Measurement of Mass, Length, and Time
Consider the following statement: “Beer costs ten.”
If we’re talking about a beer for ten dollars, it’s a little steep.
Ten Euros, it’s a
The problem is compounded when we realize the amount of beer is also unknown.
settle on $10, questions remain about this deal if
for a single draw, a can, a case or a keg.
Anything that can be counted has a
Without a unit, measured
values are meaningless.
After all, the point of a measurement is to tell us how much
systems of units
exist around the world.
You are probably most familiar with the
of feet for distance and pounds for force.
MKS (meter, kilogram,
is another system used globally for science and is part of the
International System (SI)
Four fundamental units
length, time, mass and charge
are not the only physical quantities, but they
are the most basic.
Velocity (m/s), Acceleration (m/s
), Force (N or kg m/s
), Energy (J or kg m
real physical quantities
, but they are made (derived) from relationships between the most basic units.
Because the units for these
can sometimes get to be large and cumbersome, we give
them special names like Newtons (N) or Joules (J).
Anytime you must perform a calculation,
include the units in your work and break them down to their most basic forms if necessary to cancel any
Units in calculations can always signal when something might be wrong, such as a velocity that
comes out in
hours per miles
because we performed the calculation upside down!
Most of the time when reporting measurements we will do so in standard units (m, kg, s).
measurements are small, they will often be recorded in smaller units (cm, mm, g, etc.).
It is important to
know how the metric prefixes modify the base units, and to be able to convert them accordingly.
Modification to Base Unit
or ÷ 1 trillion
0.3pF = 3 × 10
or ÷ 1 billion
532nm = 5.32 × 10
or ÷ 1 million
m = 3.6 × 10
or ÷ 1,000
256ms = 0.256s
or ÷ 100
2.5cm = 0.025m
or × 1,000
78.5g = 0.0785kg
or × 1 million
500MJ = 5 × 10
or × 1 billion
8.21GW = 8.21 × 10
or × 1 trillion
2TB = 2 × 10
Special Note: Even though kg are not the base unit, in SI
the “kg” is the standard unit.
It is a mystery.