1. Measurement is used to measure quantities
1.4 Units of Measurement
Unit is the smallest component of a whole
The units used for scientific measurements are those of the metric system
Measurement is used to measure quantities
Quantity is something that has magnitude, size, or amount (volume, length).

2. Time: To answer the question, “How long did it take?”
Length:   “How far?” question involves being able to measure the distance between two points.
10 (meaningless)
10 cm or inch
Time:  To answer the question, “How long did it take?”
When a number represents a measured quantity, the units of that quantity must always be specified

3. Scientists all over the world use (since1960) a single measurement system called SI units (Système International )
The SI consists of
Base units
Derived units
The set of base units comprises an irreducible set of units for measuring all physical variables
The derived units can be expressed in terms of the base units

4. SI Base Units
The most common base units that we will study include

5. 109 gram = ?
nanogram, ng
106 Second = ?
microsecond, s
103 meter = ?
millimeter, mm

6. Length The SI standard unit for length is the meter (m).
A distance of 1m is about the width of an average doorway.
To express longer distances, the kilometer (km) is used. One kilometer is equal to 1000 m.
To express shorter distances, the centimeter (cm) is used. One centimeter is equal to 1/100 of a meter.
Length can be measured using a meter stick or rulers.

7. Mass
Mass is a measure of the quantity of matter. The standard unit for mass is the kilogram (kg).
This base unit is unusable because it uses a prefix, kilo- instead of the word gram alone. Other units for mass are obtained by adding prefixes to the world gram
The gram (g), which is 1/1000 of a kg is used for measuring masses of small objects.

8. Time The standard unit of measurement for time is the second (s)
Larger amounts of time are measured in minutes and hours
There are 60 seconds in one minute. There are 60 minutes in one hour. Given that there are 24 hours in one day

9. Temperature
Temperature is a measure of the hotness or coldness of an object.
The standard unit of measurement for temperature is degrees Kelvin (K).
Temperature can also be measured in degrees Celsius (C) and degrees Fahrenheit (F).

10. K= C
or C = ( F  32)/1.8
or F = (C  32)1.8 or

11. Derived units
Derived units are combinations of base units. They are produced by multiplying or dividing standard units. The derived units we will study include:
Quantity
Quantity symbol
Unit
Unit abbreviation
Area A
square meter m2
Volume V
cubic meter m3
Density D
kilograms per cubic meter
kg/m3

12. Area Area is length times the width. It is expressed as square meters.
Area can also be expressed as cubic centimeters.
Area of a rectangle
16 cm cm
1111

13. Volume
The most commonly used metric units for volume are the liter(L) and the milliliter (mL)
A liter is a cube 1 dm long on each side
A milliliter is a cube 1 cm long on each side

14. density
Density is the ratio of mass to volume, or mass divided by volume. It can be written:
density = mass/volume or d = m/V
Density does not depend on the size of the sample. As the mass of an object increases, its volume increases.