How to evaluate the density of water at different uncertainties!

Varies with temperature. 4 The maximum density of pure water is 1 kilogram cubic decimeter, and if there are other impurities in the water that may change its density, such as the density of seawater is kilogram cubic decimeter. If it is under high pressure, it is possible to increase the density of the water.

Water is one of the most common substances on Earth, with a density of 1g cm3 and a density of 1000kg m3 at a temperature of 4°C. Water is an inorganic substance composed of two elements, hydrogen and oxygen.

At the same air pressure, the temperature is higher than 4 degrees Celsius.

, the higher the temperature, the less dense the water; When it is below 4°C and above 0°C, the lower the temperature, the less dense the water will be. If it is below 0°C, which is the state of ice, the density is maintained at water vapor.

The density of liquid water is greater than that of ice and water vapor.

It is mainly determined by the arrangement of molecules. It can also be said to be caused by hydrogen bonding. Due to water molecules.

It has strong polarity and can be combined into associative molecules by hydrogen bonding. Liquid water, in addition to simple water molecules (H2O), also contains association molecules (H2O)2 and (H2O)3, etc., when the temperature is 0°C when the water is not frozen, most water molecules exist as (H2O)3 association molecules.

When the temperature rises to °C, the water molecules mostly exist in the form of (H2O)2 associated molecules, and the relative rot between the molecules occupying the void decreases, and the density of water is the largest at this time. If the temperature continues to rise above °C, the general substance expands and contracts coldly.

The law is dominant.

Water has the characteristics of abnormal expansion: when the temperature of the water limb is higher than 4, with the increase of temperature, the density of water is getting smaller and smaller, when the water temperature is lower than 4, with the decrease of temperature, the density of water is getting smaller and smaller, so the density of water is maximum at 4 When the water solidifies into ice, the mass remains the same, and the volume beam is hungry to become larger, so the density becomes smaller

So the answer is: big; Small

The volume of the wall was calculated using the total area of the wall of 720m and the thickness of the wall of 25cm.

v=720m²

The volume of a brick v1=

The number of blocks required is n=v v1=180

Total mass of bricks: m=pv==

The number of trains required is n=m 4=

Basic principle. The volume of the utilized water + the volume of the sand is 10dm, the mass of the water + the mass of the sand is v1 + v2 = 10; m1+m2= can be obtained.

The specific process. Let the sand content of the Yellow River water be: a It indicates that there is akg of sand per cubic meter of water.

The volume of the sample is 10 dm, combined:

Then the quality of the sand in the Yellow River water is:

The volume of sand is v sand = m p =

Then the mass of water is: m water =

The volume of water is: v water =

Then find a according to the density of water of 10 kg m

i.e.: p water = m water v water = (

A=30kg

In mathematics, variance (s) is generally used to express s2 {(x1 x) 2+(x2-x) 2+(x3-x) 2......＋xn-x)^2｝/(n-1)。

Note: x is the average chain comic value.

n is the number of measurements.

The greater the variance, the greater the uncertainty.

the larger; The smaller the variance, the less uncertainty it has.