Approximate Times of Familiar Events
Age of Earth
2 x 10
Human Life Span
2 x 10
Earth Rotation Around Sun
3 x 10
Earth Rotation Around Axis
8.64 x 10
Time Between Heart Beats
Most physical quantities have units that are combinations of the three fundamental dimensions
of length, mass, and time. When these dimensions or measurements are combined, they produce
what are referred to as derived units. This means that they have been "derived" from one or
more fundamental measurements. These combinations of fundamental measurements can be the
combination of the same or different units. The following are examples of various derived units.
Area is the product of two lengths (e.g., width x length for a rectangle); thus, it has
the units of length squared, such as square inches (in. ) or square meters (m ).
1 m x 1 m = 1 m2
4 in. x 2 in. = 8 in.2
Volume is the product of three lengths (e.g., length x width x depth for a rectangular
solid); thus, it has the units of length cubed, such as cubic inches (in. ) or cubic meters
(m ). The MKS and CGS unit systems have a specific unit for volume called the liter
(l). One liter is equal to 1000 cubic centimeters (1 l = 1000 cm ).
2 in. x 3 in. x 5 in. = 30 in.3