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1.2 Physical Quantities and Units -- Part 1

- The theories deal with the very small and the very fast.
- The behavior of small objects traveling at high speeds or experiencing a strong gravitational field is described by the combination of these two theories.
- Theoretical quantum mechanics is the best theory we have.
- The other theories are used whenever they will produce accurate results because of its mathematical complexity.
- We can do a lot of modern physics with the math used in this text.

- A friend tells you that he has learned something.

- If you don't know the details of the law, you can still infer that the information your friend has learned is in line with the laws of nature.
- If the information was a theory, you would be able to infer that it will be a generalization.

- You can learn about graphs.
- As the constants are adjusted, the shape of the curve changes.

- The distance from Earth to the Moon may seem large, but it is just a small fraction of the distances from Earth to other bodies.

- There are many objects and phenomena studied in physics.
- There are enough factors of 10 from the tiny sizes of sub-nuclear particles to the force by a jumping flea between Earth and the Sun.
- Giving numerical values for physical quantities and equations for physical principles allows us to understand nature more deeply.
- We must have accepted units in which to express them to comprehend these vast ranges.

- We define distance and time by specifying methods for measuring them, while we define average speed by stating that it is calculated as distance traveled divided by time of travel.

- The length of a race can be expressed in units of meters or kilometers.

- It would be difficult for scientists to express and compare measured values in a meaningful way without standardized units.

- The distances given in unknown units are useless.

- The metric system is also the standard system agreed upon by scientists and mathematicians.
- The French Systeme International is where the acronym "SI" comes from.

- The SI units are given in Table 1.1.
- The text uses non-SI units in a few applications, such as the measurement of blood pressure in millimeters of mercury.
- Non-SI units will be tied to SI units through conversions whenever they are discussed.

- Some physical quantities are more fundamental than others, and the most fundamental physical quantities can only be defined by the procedure used to measure them.
- The fundamental physical quantities are taken to be length, mass, time, and electric current.

- It used to be defined as 1/66,400 of a mean solar day.

- Cesium atoms can be made to vibrate in a way that can be observed and counted.
- The time required for 9,192,631,770 of these vibrations was redefined in 1967.
- All measurements are expressed in terms of fundamental units and can't be more accurate than the fundamental units themselves.

- An atomic clock such as this one uses the vibrations of cesium atoms to keep time to a precision of better than a microsecond per year.
- The second unit of time is based on these clocks.
- The distance from the equator to the North Pole was first defined in 1791.
- The distance between two engraved lines on a Platinumiridium bar was redefined in 1889.
- By 1960, it was possible to define the meter in terms of the wavelength of light, so it was again redefined as 1,650,763.73 wavelength of orange light.
- In 1983, the meter was given its current definition as the distance light travels in a vacuum.
- The speed of light is defined by this change.
- If the speed of light is measured with greater accuracy, the length of the meter will change.

- The distance light travels in a second in a vacuum is known as the meter.
- The distance traveled is determined by the speed at which it is traveled.

- The United States' National Institute of Standards and Technology, or NIST, located in Gaithersburg, Maryland outside of Washington D.C., is one of several locations around the world where replicas of the kilogram are kept.
- The standard mass could be compared to determine the determination of all other mass.
- Even though the cylinder was resistant tocorrosion, airborne contaminants were able to adhere to its surface, slightly changing its mass over time.
- The scientific community adopted a more stable definition of the kilogram in May.
- The kilogram is defined in terms of the second, the meter, and the constant, h, which is a quantum mechanical value that relates a photon's energy to its Frequency.

- When electricity and magnetism are present, the ampere and electric current will be introduced.
- The first modules in this textbook are about mechanics, fluids, heat, and waves.

- The units are categorized by factors of 10 in the metric system, making it convenient for scientific and engineering calculations.
- The table gives metric prefixes and symbols for various factors.

- The advantage of metric systems is that they only involve powers of 10.
- There are 100 centimeters in a meter, 1000 centimeters in a kilometer, and so on.
- The relationships in nonmetric systems are not as simple as in the U.S. customary units.
- The same unit can be used over large ranges of values simply by using an appropriate metric prefix.
- The tiny measure of nanometers is convenient in optical design, while distances in meters are suitable in construction.
- There is no need for new units in the metric system.

- The power in the metric system is represented by an order of magnitude.
- There are different orders of magnitude.
- The quantities that can be expressed as a product of a specific power are said to be of the same order of magnitude.

- The scale of a value can be estimated with the order of magnitude.
- The greatest accuracy and precision in measurement can be found in the fundamental units described in this chapter.
- Physicists feel that it would be more satisfying to base our standards of measurement on fundamental physical phenomena such as the speed of light, because there is an underlying substructure to matter.
- The standard of time is based on the oscillations of the cesium atom.

- The wavelength of light used to be the standard for length, but it has been replaced by the more precise measurement of the speed of light.
- If it becomes possible to measure the mass of atoms or a particular arrangement of atoms to greater precision than the kilogram standard, it may become possible to base mass measurements on the small scale.
- Current and charge are related to large-scale currents and forces between wires, but electrical phenomena on the small scale may someday allow us to base a unit of charge on the charge of electrons and protons.

- The wide range of examples of known lengths, mass, and times can be seen in Table 1.3.
- You can get a feel for the range of possible topics and numerical values by examining this table.

- The tiny plants swim in the ice.
- They can be as small as a few micrometers and as long as 2 millimeters in length.

- There are 2.4 billion light years away from Earth.
- Nature has a wide range of observable phenomena.

- Sometimes it is necessary to convert from one type of unit to another.
- If you are reading a European cookbook, some quantities may be expressed in units of liters and you need to convert them to cups.
- You are interested in how many miles you will be walking if you read walking directions from one location to another.
- You will need to convert units of feet to miles.

- An example of how to convert units is presented.
- We want to convert 80 meters to kilometers.

- List the units that you have and the units that you want to convert to.
- We want to convert the units in meters to kilometers.

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