科学计量

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Measurements are a basic necessity in science. Scientists have designed thousands of different tools to help in the vital process of measuring. In this image of the control panel of the space shuttle Atlantis, we see dozens of readouts from measuring systems.
::测量是科学的基本必要条件。 科学家已经设计了数千种不同的工具来帮助重要的测量过程。 在亚特兰蒂斯航天飞机控制板的图像中,我们看到了测量系统的数十种读数。

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Measurement
::计量度量度量度量度度量度度度度量度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度度

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We already know that observations are an important part of the . Hypotheses are accepted or rejected based on how well they explain observations. Some observations, such as "the plant turned brown" are qualitative ; these observations have no associated numbers. A quantitative observation includes numbers, and is also called a measurement . A measurement is obtained by comparing an object to some standard. Any observation is useful to a scientist, but quantitative observations are commonly considered more useful. Even if the measurement is an estimate, scientists usually make quantitative measurements in every experiment.
::我们已经知道观测是观测的一个重要部分。根据对观测的解释,假设被接受或否定。有些观察,例如“植物变棕”是定性的;这些观察没有相关数字。定量观察包括数字,也称为测量。通过比较对象和某种标准,可以得出测量结果。任何观察对科学家都有用,但一般认为定量观察更有用。即使测量是一种估计,科学家通常在每次实验中都进行定量测量。

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Consider the following pair of observations.
::考虑以下两条意见。

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1. When the volume of a gas is decreased, its pressure is increased.
   ::当气体的体积减少时,压力就会增加。
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2. When the volume of a gas is reduced from 2.0 liters to 1.0 liter, the pressure increases from 3.0 atm to 6.0 atm.
   ::当气体的体积从2.0升降至1.0升时,压力从3.0 小时增加到6.0 小时。

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A great deal more information, and more useful information, is available in the second observation.
::第二项意见提供了大量更多的信息和更有用的信息。

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Since accurate measurement is a vital tool for doing science, a consistent set of units for measurement is necessary. Physicists throughout the world use the International System of Units (also called the SI system). The SI system is basically the metric system, which is convenient because units of different size are related by powers of 10. The system has physical standards for length, mass, and time. These are called fundamental units because they have an actual physical standard.
::由于精确测量是科学工作的一个重要工具,需要有一套一致的计量单位,世界各地的医生都使用国际单元系统(也称SI系统),SI系统基本上是衡量系统,因为不同大小的单位有10倍的功率,因此很方便,该系统有长度、质量和时间的物理标准,被称为基本单位,因为它们有实际的物理标准。

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The standard SI unit for length is the meter , and is denoted by "m". Originally, the meter was defined as the length between two scratches on a piece of metal which was stored in a secure vault under controlled conditions. The meter's definition has changed over time, but it is now accepted to be the light travels in a vacuum over 1/299792458 of a second.
::标准SI单位的长度是表,用“m”表示。 最初,该表被定义为在受控制条件下存放在安全保险库的金属碎片两道刮痕之间的长度。 计时器的定义随着时间的推移发生了变化,但现在被接受为光线在真空中行走的时间超过1/2997992458秒。

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The standard unit of time, the second , was once defined as a fraction of the time it takes the earth to complete an orbit around the sun, but has now been redefined in terms of the frequency of one type of radiation emitted by a cesium-133 atom. Seconds are denoted by "s" or, less commonly, "sec."
::标准时间单位,第二个,曾经被界定为地球完成太阳周绕轨道所需的时间的一小部分,但现在又被重新界定为-133原子发射的一类辐射的频率。第二组用“s”或较不常见的“sec”表示。

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The standard unit for mass is the kilogram . For 143 years the kilogram standard was a block of platinum-iridium metal kept near Paris, France. In 2019 the standard was changed to define the kilogram in terms of the Planck constant instead of a physical object which could change over time. A kilogram is denoted "kg" and is a multiple of the smaller unit of mass, the gram ("g").
::标准质量单位为千克。143年来,千克标准是法国巴黎附近的一个金属块。2019年,对标准进行了修改,以用普朗克常数而不是可能随时间变化的物理物体来定义千克。一千克是“千克”的表示,是较小质量单位(克)的倍数。

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Meters, seconds, and kilograms are not the only unit entities. Take, for example, . Speed is a derived unit, measured in meters per second (m/s). Derived units are units that are expressed using combinations of the fundamental units.
::鼠、 秒、 公斤并非唯一的单位实体。 例如, 速度 。 速度 是一个衍生单位, 以每秒( m/ s)米计。 衍生单位是使用基本单位组合表示的单位 。

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As mentioned earlier, the SI system is a decimal system. Prefixes are used to change SI units by powers of ten. Thus, one hundredth of a meter is a centimeter and one thousandth of a gram is a milligram.  The for all quantities use the same prefixes. One thousand meters is a kilometer and one thousand grams is a kilogram. The common prefixes are shown in the Table .
::如前所述,SI系统是一个小数系统,用十倍功率改变SI单位时使用前缀。因此,一公分的十分之一是一厘米,一公克的千分之一是一毫克。所有数量都使用相同的前缀。一千米是一公里,一千克是一公斤。共同的前缀在表格中显示。

Common Prefixes Used with SI Units

Prefix	Symbol	Fractions	Example
pico	p	1 × 10 -12	picometer (pm)
nano	n	1 × 10 -9	nanometer (nm)
micro	μ	1 × 10 -6	microgram (μg)
milli	m	1 × 10 -3	milligram (mg)
centi	c	1 × 10 -2	centimeter (cm)
deci	d	1 × 10 -1	decimeter (dm)
		Multiples
tera	T	1 × 10 12	terameter (Tm)
giga	G	1 × 10 9	gigameter (Gm)
mega	M	1 × 10 6	megagram (Mg)
kilo	k	1 × 10 3	kilogram (kg)
hecto	h	1 × 10 2	hectogram (hg)
deca	da	1 × 10 1	decagram (dag)

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These prefixes are defined using scientific notation. Numbers with different prefixes can be shown as equalities when they are equivalent measurements. For example, 1 meter = 100 centimeters. Similarly, 0.01 meters = 1 centimeter. These equivalencies are used as conversion factors when units need to be converted.
::这些前缀是用科学符号来定义的。在等量测量时,不同前缀的数字可以显示为等值。例如,1米=100厘米。类似地,0.01米=1厘米。当单位需要转换时,这些等值被用作换算系数。

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Examples
::实例

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Example 1
::例1

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Convert 500 millimeters to meters.
::将500毫米转换成米

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The equivalency statement for millimeters and meters is 1000 mm = 1 m.
::毫米和米的等值说明为1000毫米=1米。

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To convert 500 mm to m, we multiply 500 mm by a conversion factor that will cancel the millimeter units and generate the meter units. This requires that the conversion factor has meters in the numerator and millimeters in the denominator.
::要将500毫米转换为m,我们乘以500毫米转换系数,该系数将取消毫米单位并生成计量单位。这要求转换系数在分子和分母中计有米。

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500 mm is equivalent to 0.5 m.
::500毫米等于0.5米。

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Example 2
::例2

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Convert 11 µg to mg.
::将11微克转换为毫克。

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When converting from one prefix to another, such as in this problem, it is usually easiest to convert through the base unit. In this case, the base unit is grams, so we use the two following equivalency statements:
::在从一个前缀转换为另一个前缀时,例如在此问题上,通常最容易通过基单元转换。在这种情况下,基单元是克,因此我们使用以下两个等效说明:

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$\begin{array}{r}1\times {10}^6\mu \text{g}=1\text{g and}1000\text{mg}=1\text{g}\end{array}$
::1x106微克=1克和1000毫克=1克

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The first conversion factor converts from micrograms to grams and the second conversion factor converts from grams to milligrams.
::第一个换算系数从微克转换为克,第二个换算系数从克转换为毫克。

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$\begin{array}{r}(11\mu \text{g})\left(\frac{1\text{g}}{1\times {10}^6\mu \text{g}}\right)\left(\frac{1000\text{mg}}{1\text{g}}\right)=1.1\times {10}^{-2}\text{mg}\end{array}$
:11微克(1克1x106微克)(1 000毫克1克)=1.1x10-2毫克)

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11 µg is 1.1 × 10 ^-2  mg.
::11微克为1.1×10-2毫克。

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The key to converting units is to think of these equivalency statements as a creative way of multiplying by one. You can multiply any number by one at any time because it does not change the number. Play around with converting between different measuring systems using equivalencies and the creative multiplication of one strategy in the following simulation:
::转换单位的关键是将这些等效声明视为一个乘以一个的创造性方式。 您可以随时将任何数字乘以一个, 因为它不会改变数字。 玩弄不同测量系统之间的转换, 使用等效和在以下模拟中创造性地乘以一个战略:

 

 

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Further Reading
::继续阅读

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Summary
::摘要

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• Measurements (quantitative observations) are often more useful than qualitative observations.
  ::衡量(定量观测)往往比定性观测更有用。
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• The system of units for measurements in physics is the SI system.
  ::物理测量单位系统是SI系统。
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• The fundamental quantities in the SI system are length, mass, and time.
  ::SI系统的基本数量是长度、质量和时间。
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• The SI unit for length is the meter, for time is the second, and for mass is the kilogram.
  ::SI单位的长度是计数器,时间是第二个,质量是千克。
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• Prefixes are used to change SI units by powers of ten.
  ::使用前缀用十倍的权力改变SI单位。
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• Equivalencies are used as conversion factors when units need to be converted.
  ::当单位需要转换时,将等值用作换算系数。

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Review
::回顾

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1. Which of the following are quantitative observations?
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   1. The sky is blue.
      ::天空是蓝色的。
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   2. The toy car is about 3 inches long.
      ::玩具车长约3英寸
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   3. It is 250,000 miles from the earth to the moon.
      ::从地球到月球还有25万英里
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   4. The wooden cart has a mass of 18.654 g.
      ::木制车的重量为18,654克。
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   5. When at rest, the pendulum points toward the center of the earth.
      ::当休息时,钟摆指向地球的中心。
   
   ::以下哪些是定量观测?天空是蓝色的。 玩具车长约3英寸。 距离地球到月球有25万英里。 木制木制车质量为18, 654克。 休息时, 钟摆点指向地球中心 。
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2. Convert 76.2 kilometers to meters.
   ::转换76.2公里到米
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3. Convert 76.2 picograms to kilograms.
   ::将76.2象形图转换成公斤。
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4. Convert 1 day into seconds.
   ::将一天转换为秒。

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Explore More
::探索更多

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Use the resource below to answer the questions that follow.
::利用以下资源回答以下问题。

 

 

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1. Draw for yourself the conversion base used in this video.
   ::绘制此视频使用的转换基数 。
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2. Convert 6.6 meters to centimeters using the process shown.
   ::使用所显示的过程将6.6米转换为厘米。
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3. Convert 1 mile to feet. Then convert to inches. Then convert to centimeters. How many centimeters are in a mile?
   ::将1英里转换为英尺。然后转换为英寸。然后转换为厘米。一英里内有多少厘米?
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4. At 2:29 in the video, he motions across and then down in solving the problem. What is the mathematical process he is doing?
   ::在2点29分的视频中,他走过一圈,然后下来解决问题。他正在做的数学过程是什么?