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The SI base unit of time is the second (s)    . Small and large time intervals can be expressed with the appropriate prefixes; for example, 3 microseconds = 0.000003 s = 3 × 10 −6 and 5 megaseconds = 5,000,000 s = 5 × 10 6 s. Alternatively, hours, days, and years can be used.

Derived si units

We can derive many units from the seven SI base units. For example, we can use the base unit of length to define a unit of volume, and the base units of mass and length to define a unit of density.


Volume is the measure of the amount of space occupied by an object. The standard SI unit of volume is defined by the base unit of length ( [link] ). The standard volume is a cubic meter (m 3 )    , a cube with an edge length of exactly one meter. To dispense a cubic meter of water, we could build a cubic box with edge lengths of exactly one meter. This box would hold a cubic meter of water or any other substance.

A more commonly used unit of volume is derived from the decimeter (0.1 m, or 10 cm). A cube with edge lengths of exactly one decimeter contains a volume of one cubic decimeter (dm 3 ). A liter (L)    is the more common name for the cubic decimeter. One liter is about 1.06 quarts.

A cubic centimeter (cm 3 ) is the volume of a cube with an edge length of exactly one centimeter. The abbreviation cc (for c ubic c entimeter) is often used by health professionals. A cubic centimeter is also called a milliliter (mL)    and is 1/1000 of a liter.

Figure A shows a large cube, which has a volume of 1 meter cubed. This larger cube is made up of many smaller cubes in a 10 by 10 pattern. Each of these smaller cubes has a volume of 1 decimeter cubed, or one liter. Each of these smaller cubes is, in turn, made up of many tiny cubes. Each of these tiny cubes has a volume of 1 centimeter cubed, or one milliliter. A one cubic centimeter cube is about the same width as a dime, which has a width of 1.8 centimeter.
(a) The relative volumes are shown for cubes of 1 m 3 , 1 dm 3 (1 L), and 1 cm 3 (1 mL) (not to scale). (b) The diameter of a dime is compared relative to the edge length of a 1-cm 3 (1-mL) cube.


We use the mass and volume of a substance to determine its density. Thus, the units of density are defined by the base units of mass and length.

The density    of a substance is the ratio of the mass of a sample of the substance to its volume. The SI unit for density is the kilogram per cubic meter (kg/m 3 ). For many situations, however, this as an inconvenient unit, and we often use grams per cubic centimeter (g/cm 3 ) for the densities of solids and liquids, and grams per liter (g/L) for gases. Although there are exceptions, most liquids and solids have densities that range from about 0.7 g/cm 3 (the density of gasoline) to 19 g/cm 3 (the density of gold). The density of air is about 1.2 g/L. [link] shows the densities of some common substances.

Densities of Common Substances
Solids Liquids Gases (at 25 °C and 1 atm)
ice (at 0 °C) 0.92 g/cm 3 water 1.0 g/cm 3 dry air 1.20 g/L
oak (wood) 0.60–0.90 g/cm 3 ethanol 0.79 g/cm 3 oxygen 1.31 g/L
iron 7.9 g/cm 3 acetone 0.79 g/cm 3 nitrogen 1.14 g/L
copper 9.0 g/cm 3 glycerin 1.26 g/cm 3 carbon dioxide 1.80 g/L
lead 11.3 g/cm 3 olive oil 0.92 g/cm 3 helium 0.16 g/L
silver 10.5 g/cm 3 gasoline 0.70–0.77 g/cm 3 neon 0.83 g/L
gold 19.3 g/cm 3 mercury 13.6 g/cm 3 radon 9.1 g/L

While there are many ways to determine the density of an object, perhaps the most straightforward method involves separately finding the mass and volume of the object, and then dividing the mass of the sample by its volume. In the following example, the mass is found directly by weighing, but the volume is found indirectly through length measurements.

Questions & Answers

what is aromaticity
Usman Reply
what is caustic soda
Ogbonna Reply
sodium hydroxide (NaOH)
what is distilled water
is simply means a condensed water vapour
advantage and disadvantage of water to human and industry
Abdulrahman Reply
a hydrocarbon contains 7.7 percent by mass of hydrogen and 92.3 percent by mass of carbon
Timothy Reply
how many types of covalent r there
JArim Reply
how many covalent bond r there
they are three 3
TYPES OF COVALENT BOND-POLAR BOND-NON POLAR BOND-DOUBLE BOND-TRIPPLE BOND. There are three types of covalent bond depending upon the number of shared electron pairs. A covalent bond formed by the mutual sharing of one electron pair between two atoms is called a "Single Covalent bond.
what is an atom
Rabiu Reply
why is an atom
u answer me first
Atom is indivisible particles which take place in chemical reactions
what is neck mi nut
Hernandez Reply
what is half reaction?
Makinde Reply
wat is the chemical formular for zinc hydrozide
Ani Reply
what is atomicity
Simbiat Reply
A 45 ml of ph=1,hcl was reacted with a 55l ml of ph=13, naoh solution . what is the final ph
chamini Reply
what is coordination number
coordination number is the number of atoms or ions immediately surrounding a central atom in a complex or crystal
what is isotope
who is the father of chemistry
Roland Reply
Antoine Lavoisier. Father of modern chemistry
What is geometric isomerism
Imoh Reply
pls I don't really know teach me
geometric isomerism are molecules that are locked into their spatial position with respect to one another due to a double Bond or ring structure
Chromatography is a physical method of seperation where by mixtures that are in two phrases are separated
Lexzzy Reply

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