In junior high school physics, only the commonly used unit of temperature is involved: Celsius, the symbol℃. Centigrade scale was founded by Swedish physicist Poerxiusi in 1742. In centigrade scale, the temperature of ice-water mixture is set to 0℃ at standard atmospheric pressure, and the temperature when water boils is set to 100℃, and it is divided into 100 equal parts between 0 ~ 100℃, and each equal part is100. In fact, the melting point of ice at standard atmospheric pressure was initially set at 100℃, and the boiling point of water was set at 0℃. In order to take care of people's habits, it was later changed to this.
The density of water is not clear, but the density unit is the derived unit. According to the definition of density, the unit of density consists of mass unit and unit of volume. The unit of mass "kg" originated in France, and it is 179 1 year. France stipulated that the mass of 1L pure water at 4℃ was 1kg, and it was made into a kilogram sample in 1799. Because it was kept in the archives at that time, it was called "archives kilogram". Later, it was accepted by the international community, and 1889, the first international metrology conference approved to prevent France's "archive kilogram" from being used as the original international kilogram device for quality measurement.
Calculate the density of water ρ = m/v =1kg/1l =1kg/l.
However, water has the property of abnormal expansion between 0 and 4℃, so 1kg/L is the maximum density of water.
You can't believe that you didn't even graduate from junior high school under the premise of a standard atmospheric pressure. Son, if you have any questions in your heart, you don't have to rush to the Internet for answers. Read a few more years and you will understand.
The boiling point of water is 100, the freezing point is 0, and the density is 1. Is it artificially specified or inferred?
This is a typical cognitive problem that can't distinguish objective laws from subjective knowledge. There are many laws in our world, which naturally exist in nature itself. People can't change the law, nor can they create it. They can only know the rules and use them to change their lives.
The objective laws of nature and people's subjective understanding are two different things. People's understanding of objective laws is correct and true, but also wrong and distorted.
For example, the understanding of solar eclipse is originally because the sun, the earth and the moon run in a straight line, and the earth and the moon block the sunlight from each other. If you realize this scientifically, you can calculate when the solar eclipse will happen again; Ancient folks thought it was a miracle phenomenon, and Tengu's swallowing the sun and the moon was a symbol of disaster.
Among them, solar eclipse is a natural law, and people's understanding is a subjective reflection of natural phenomena.
People have the same understanding of water. The phase change of water (the state of matter changes under certain conditions) is an objective natural law, which is independent of human will.
When the temperature is appropriate, water generally exists in liquid state; When it is cold to a certain temperature, it will freeze and become solid; But when the temperature rises to a certain extent, it will boil and evaporate into gas.
Under different pressures, the phase transition temperature of water will change.
Then, for the temperature of water, when it will freeze and when it will volatilize, people should make a standard, so that everyone's understanding can be unified and the same thing can be talked about when discussing problems, otherwise it will be very chaotic.
If when discussing water, everyone only knows that it is frozen, then what should be used to mark this paragraph when it is not frozen? There's nothing I can do.
Therefore, there must be a unified description standard, which is the temperature scale.
Temperature scale is a measure of natural temperature and the embodiment of subjective consciousness. Just as a person is born with a name, it doesn't change the essence of people, just to distinguish one person from another.
There are many kinds of temperature scales at first, which are determined by experience, so there are different expressions for the freezing point and boiling point of water.
In ancient times, there were Lee's scale, Langer scale, Fahrenheit scale, centigrade scale scale and so on, all of which were determined by human experience. At present, the empirical temperature scales still in use in the world are mainly Celsius and Fahrenheit.
These two temperatures are determined by using the relationship between the physical quantity of the substance and the temperature change, using experimental methods and empirical judgment.
The Fahrenheit temperature is 17 14. German Warren Hite made a glass mercury thermometer according to the change of mercury volume with temperature. He stipulated that the boiling temperature of water is 2 12 degrees, and the mixture of ammonium chloride and ice is 0 degrees. Between these two fixed points, it is divided into 2 12 equal parts, and each 1 part is 65438.
This is the Fahrenheit scale, named after Warren Hite's initials.
1740, the Swedes set the freezing point at 0 degrees Celsius and the boiling point of water at 100 degrees. The two fixed points are equally divided into 100 parts, and each 1 part is 1 degree, which is recorded as 1 degree Celsius. This is centigrade scale, named after Celsius.
The Langmuir temperature scale and Kelvin temperature scale also came from this way, but the temperature marking is more complicated, and now it has been eliminated, so I won't elaborate on it.
These empirical temperature scales have certain limitations and randomness, and it is difficult to adapt to different regions and any occasions.
Kelvin temperature scale is the standard temperature scale of modern science. 1848, the world-famous scientific master, the creator of the Atlantic submarine cable, the pioneer of electromagnetic theory and one of the founders of thermodynamics, and the famous British mathematician, physicist and engineer, Lord william thomson Kelvin, founded the thermodynamic temperature, which is the scientific scale of modern temperature scale-Kelvin temperature scale.
This is a purely theoretical temperature scale, which has nothing to do with the properties of temperature substances. The symbol is T and the unit is K (Kelvin for short).
Kelvin temperature scale is established by ideal gas, and its zero point is called absolute zero. According to the average kinetic energy equation of ideal gas molecules in thermodynamics, Ek=ikT/2.
It is concluded that when the temperature reaches absolute zero: T=0 K, the gas kinetic energy of the molecule is zero. This is the lowest temperature in our world, and it is impossible.
But the Kelvin temperature scale has only a lower limit, but no upper limit.
In order to adapt to people's habits and make the calculation more convenient, the scale of each degree of Kelvin thermometer is equal to Celsius.
Absolute zero 0 K corresponds to-273.15℃; The freezing point of water is 0℃, and the corresponding Kelvin temperature is 273.15k; ; The boiling point of water is 100℃, and the corresponding Kelvin is 373. 15K, and so on. No matter how many degrees it rises, Kelvin is 273. 15 degrees higher than Celsius.
For example, the surface temperature of the sun is about 6000K, which is about 5726.85℃. However, in the expression of high temperature in the universe, this scale difference can be basically ignored.
As can be seen from the above, natural temperature is objective and constant, and people's measurement of temperature is subjective and variable. The appearance of kjeldahl temperature scale is of great scientific significance to the world temperature scale.
At present, all the temperature scales in the world are based on the Kelvin temperature scale, which is the standard for human beings to scientifically understand the laws of nature and one of the seven basic quantities of the international system of units.
The conversion relationship between Celsius T and Kelvin T is: T(K)=273. 15+t(℃).
The conversion relationship between Fahrenheit F and Celsius T is = t (℃) x1.8+32.
The conversion result is 100℃=2 12℉/0℃=32℉.
Therefore, the conversion relationship between thermodynamic temperature scale and Fahrenheit temperature scale is: K=(F-32)×5/9+273. 15 or f = (k-273.5438+05) × 9/5+32.
But in any case, the state change of water is a natural law, and people's understanding of the phase change law of water at different temperatures is a subjective result and a correct and true reflection of human nature.
Thank you for reading and welcome to discuss.
Any data you know is just a numerical value defined by human beings for the convenience of calculation. For example, you know that 24 hours a day is such a long process. You can define it as any calculation method you like, such as 30 hours a day, or 3 hours a day, or any method you like, but the length of this process is constant. The boiling point of water is 100 degrees Celsius. The Warburg scale is not 100, but the boiling point still exists and remains unchanged. Just change it to a numerical value to give you a basic concept of cognition, calculation and comparison.
Several academicians, such as Taishang Laojun, Buddha, God and Jesus, met overnight to discuss the decision made.
Yes, your causality is reversed. At one atmospheric pressure, the freezing temperature of water is set to 0 degrees, and the boiling temperature is set to 100 degrees, because there is no such concept before.
At first, someone made a mercury thermometer to cool down and measure the temperature of newly frozen water, which was set at 0℃; After reheating, measure the boiling temperature of water and set it as100℃-that is, the freezing point of water is 0℃ and the boiling point is 100℃, which is the centigrade thermometer.
Someone put 1 ml water on the balance to weigh it, and set the weight of 1 ml water as 1 g (g), that is, the specific gravity of water (1 ml water weight) is 1 g.
If you have studied physics in middle school, you should know whether this is artificial or speculative.
It is artificially stipulated.
When you say that the boiling point of water is 100 degrees and the freezing point is 0 degrees, it is actually the definition of degrees Celsius. The degree of Celsius stipulates that at 1 standard atmospheric pressure, the temperature of the mixture of pure ice and water is defined as 0 degree, and the boiling point of water is defined as 100 degree.
So is density. Under the condition of defining standard atmospheric pressure and temperature, the density of pure water is 1.
This artificial regulation is necessary because all weights and measures must have a basic reference.
Water is the most common substance, and many weights and measures take water as the reference; Numbers 0, 1, 10, 100 are often used as reference numbers; Sphere is the most commonly used reference shape.
Scientists make the roundest measuring ball.
Asking this question, it is obvious that junior high school physics is taught by physical education teachers. You have to understand that people don't define the freezing point and boiling point temperature of water, but use the freezing point and boiling point temperature of water to define the celsius scale, define the temperature of ice-water mixture at standard atmospheric pressure as 0 degrees celsius, and then define the boiling water temperature at standard atmospheric pressure as 100 degrees celsius, and then divide it into 100 portions, each of which is 1 degree celsius.
These are all artificial rules. As a benchmark for other substances and physical quantities.
Because water is the most common substance in nature. It also has many forms, such as gaseous water vapor, solid ice, liquid water and so on.
Moreover, all kinds of substances react with water, so all kinds of substances take water as the reference and specify their density, boiling point and other values as the benchmark.