1. Measurements in Physics

2. Historical Perspective
Ancient Civilizations and Monarchies
“Cubit” local customs were used
Use of length foot to standardize measurement a king’s foot
1700’s
Scientific Renaissance. France metric system, units of 10.
1960’s
SI system is adopted worldwide
Present Day:
USA, Liberia, and Burma (or Myanmar) still use Empirical System of Measurement (inches, feet, pounds). The United Kingdom uses both systems.
The solution is a rod or bar, of an exact length, kept in a central public place. From this 'standard' other identical rods can be copied and distributed through the community. In Egypt and Mesopotamia these standards are kept in temples. The basic unit of length in both civilizations is the cubit, based on a forearm measured from elbow to tip of middle finger. When a length such as this is standardized, it is usually the king's dimension which is first taken as the norm.

3. Physical Quantities
Physical quantity: a physical property that can be measured (height, volume, temperature, and other physical properties). It is described by both a number and a unit of defined size.
61.2 kilograms
number unit
The number along isn’t useful without a unit. If you asked how much blood an accident victim had lost, the answer “tree” wouldn’t tell you much. Three drops? Three milliliters? Three pints? Three liters? (By the way, an adult human has only 5-6 liters of blood). Your car speed: 30 mi/hr, or km/hr, or m/s? All these values could give you completely different speed.

4. SI Units
SI units: units of measurement defined by International System of Units; standard units agreed upon by scientists
Mass is measured in kilograms (kg), length is measured in meters (m), volume is measured in cubic meters (m3), temperature is measured in kelvins (K), and time is measured in seconds (s).
Any physical property can be measured in many different units. For example, a person’s height might be measured in inches, feet, yards, meters, or many other units. To avoid confusion, scientists from many countries have agreed on a system of standard units, called by the French name Systeme International d’Unites (International System of Units), abbreviated SI.

5. Metric System
SI units are closely related to the more familiar metric units used in all industrialized nations of the world except the United States.

6. Comparing SI and Metric Units
Some SI and Metric Units and Their Equivalents
Quantity
SI Unit
(Symbols)
Metric Unit
(Symbol)
Equivalents
Mass
Kilogram (kg)
Gram (g)
1 kg=1000 g = lb
Length
Meter (m)
1 m= ft
Volume
Cubic meter (m3)
Liter (L)
1 m3=1000L=264.2 gal
Temperature
Kelvin (K)
Celsius Degree (⁰C)
1K = 1⁰C
1⁰C=1.8⁰F
Time
Second (s)
-----
Although SI units are now preferred in scientific research, metric units are still used in some fields.
In addition to these units, many other widely used units are derived from them. Speed, for example, is a distance covered in a given time and expressed in units of meter per second (m/s).

7. SI prefixes Prefix Symbol Meaning (fraction form) (decimal form)
Example
kilo- k
1000
1 kilogram (kg) = 1000 g
hecto- h
100
1 hectogram (hg) = 100 g
deka- da 10
1 decaliter (daL) = 10 L
deci- d 1_
0.1
1 deciliter (dL) = 0.1 L
centi- c
0.01
1 centimeter (cm) = 0.01 m
milli- m
1__
0.001
1 milligram (mg) = 0.001g
micro- μ
1____
1 micrometer (μm) = m
One problem with any system of measure is that the sizes of the units are often too large or too small for the problem at hand. A biologist describing the diameter of a red blood cell ( m) would find the meter to be too large. However, astronomer measuring the average distance from the earth to the sun (150,000, 000, 000 m) would find the meter to be too small. For this reason, metric and SI units can be modified by prefixes to refer to either smaller or larger quantities.
SI unit for mass – the kilogram – differs by the prefix kilo- from the metric unit gram. Kilo- indicates that that a kilogram is 1000 times larger then a gram.
1 kg = 1000 x 1g = 1000g
Small quantities are often reported in milligrams (mg). The prefix milli- shows that the unit gram has been divided by 1000, which is the same as multiplying by 0.001:
1 mg = 1g/1000 = 1/1000 x 1g = x 1g = 0.001g

8. Fundamental SI Units Fundamental SI units:
Standard units agreed upon by scientists
Mass:
kilograms (kg)
A measure of an object inertia or resistance to change in motion
Length:
meter (m)
Distance between two points
Time:
seconds (s)
How long?

9. Derived Units Derived Units:
Combination of two or more fundamental units
Volume:
The cubic meter (m3)
The amount of space occupied by an object
Volume = length x width x height
V = l x w x h
Density:
The physical property that relates the mass of an object to its volume
Mass per unit volume: grams per cubic centimeter (g/cm3) for solids or grams per milliliter (g/mL) for liquids
Density = mass (g) / volume (mL or cm3)

10. Measuring Mass
Mass:
A measure of an object inertia or resistance to change in motion
A measure of the amount of matter in an object
W eight:
A measure of the gravitational force that the Earth, moon, or other large body exerts on the object.
Mass and Weight:
The amount of matter (mass) in an object does not depend on location. However, the weight of the object does depend on location.
At the same location, two objects with identical masses have identical weights; that is, gravity pulls on both equally. Thus, the mass of an object can be determined by comparing the weight of the object to the weight of a known reference standard.
Whether you are standing on the earth or on the moon, the mass of your body is the same. Your weight on earth might be 140 lb, but it would be 23 lb on the moon because the pull of gravity there is only about 1-sixth as great.
We speak of “weighing” when we really mean that we are measuring mass by comparing two weights

11. Units of Mass Unit Equivalent 1 kilogram (kg)
= 1000 grams (g) = pounds (lb)
1 gram (g)
= kilogram (kg) = 1000 milligrams (mg)
= ounce (oz)
1 milligram (mg)
= gram = kilogram (kg)
1 ton (t)
= 2000 pounds = kilograms (kg)
1 pound (lb)
= 16 ounces = kilogram (kg)
= 454 grams (g)
1 ounce (oz)
= kilogram (kg) = grams (g)
= 28,350 milligrams

12. Units of Mass
The kilogram is a mass of platinum-iridium cylinder preserved at the International Bureau of Weight and Measures in France.
It was defined as mass of one liter (1000 cubic centimeters) of water at the temperature at which it is most dense (4⁰C).

13. Measuring Length Length: Distance between two points
The meter is the standard measure of length, or distance, in both the SI and metric systems.
One meter is inches, or about 10% longer than one yard.
More commonly used measures of length are the centimeter (cm; 1/100 m) and the millimeter (mm; 1/1000 m)
One centimeter is a bit less then half an inch = inch
One millimeter is inch, or about the thickness of a dime.
One meter is a length that is much too large for many measurements

14. Units of Length

15. Units of Length

16. Units of Length
1 Meter:
Was defined in terms of the distance from the North Pole to the equator. It equals approximately one ten-millionth of the distance from the North Pole to the equator.
Equals the length of the path traveled by light in vacuum during a time interval of 1/ of a second.
This distance is close to 10 million meters.

17. Units of Time Time: The second is the SI unit of time
Until 1956 it was defined in terms of the mean solar day. There were seconds per day. Second was defined as 1/86400 of the mean solar day. However, the rate of rotation of the Earth is gradually slowing.
In 1956 the mean solar day of the year 1900 was chosen as the standard on which to base a second.
Since 1956, the second is defined as time taken by a cesium-133 atom to make vibrations.
One solar day was divided into 24 hours. Each hour was divided into 60 min and each min into 60 seconds.

18. Units of Volume Volume: The amount of space occupied by an object
The SI unit for volume is the cubic meter, m3. It is so large that the liter (1 L = m3 = 1 dm3) is much more commonly used.
One liter has the volume of a cube 10cm
(1 dm) on edge and is a bit larger then one U.S. quart.
Each liter is further divided into 1000 milliliters (mL), with 1 mL the size of a cube 1 cm on edge, or 1 cm3

19. Units of Volume

20. Units of Volume