1.2. Fundamental Units and Standard Units http://www.ck12.org
1.2 Fundamental Units and Standard Units
Objectives
- List and use fundamental units in the study of mechanics.
- List and use standard units in the study of mechanics.
- Use dimensional analysis.
Vocabulary
- dimensional analysis:Checking your mathematical equations by keeping units with every number, or pre-
dicting units based on the relation of other units. - length:The measurement of the extent of something along its greatest dimension.
- mass:A property of matter equal to the measure of an object’s resistance to changes in either the speed or
direction of its motion. The mass of an object is not dependent on gravity and therefore is different from but
proportional to its weight. - meter stick:A ruler exactly one meter in length.
- scalar:A quantity, such as mass, length, or speed that is completely specified by a single number. It is said to
have magnitude, but no direction. - SI units:The most modern version of the metric system, also known as the International System of Units (SI).
- time:An ordered continuum in which events occur in succession from the past through the present to the
future. - vector:A quantity, such as velocity or force, that must be completely specified by both a magnitude and
a direction. For example, if an object is moving, we must know both the amount of motion as well as the
direction of motion to know the vector quantity velocity.
Equations Including Units
Mathematics is central to science in general and especially physics. The math in physics is always connected to real
physical quantities, however. In a math class, an equation might read:
24 −^12 × 10 ×( 2 )^2 = 10
However, in physics all numbers represent a specific physical quantity and they have units.
24 m−^12 × 10 ms 2 ×(2 s)^2 =4 m
Each of the quantities in the equation has abbreviations for units beside it. For example, this is the formula for how
high an object would be after dropping for two seconds from the top of a six-story building.
Standard Units—SI Units (Standard International Units)
Especially in scientific work, it is vital that we use a consistent and logical set of units. For almost all scientists, that
system is theInternational System of Units, abbreviatedSI. This the most modern form of the metric system. It
is used universally for all scientific work. It is also used on a daily basis in almost all the world. The three countries
that do not officially use metric units in some form today are Burma, Liberia, and the United States.