"Density and Social Life" Quality and Density PPT Courseware 2

Description

"Density and Social Life" Quality and Density PPT Courseware 2

【Learning Content】

1. Application of density in production and life

2.The relationship between density and temperature

3. Thermal expansion and contraction, abnormal expansion of wind and water

Applications of density in life

(1) During field exploration, exploration team members can determine mineral deposits, types and their economic value by collecting information such as sample density.

(2) On the wheat field, people use wind power to winnow the wheat field and sort the full wheat grains from shriveled grains and grass clippings.

(3) Choose appropriate materials according to different needs.

In transportation and aviation equipment, high-strength, low-density alloy materials, fiberglass and other composite materials are often used;

In product packaging, foam plastics with low density are often used as fillers, which are shock-proof, easy to transport and low in price.

Reading summary The application of density in life:

1. Exploring mineral deposits and collecting sample information (density, etc.)

2. Wind-driven elevating and elevating machines work by using the principle of different densities to separate finished grain, secondary grain, stones and grass clippings.

3. Select brine, flotation coal powder, and make cocktails

4. Choose different materials based on density knowledge:

(1) Cars and airplanes often use high-strength, low-density materials (alloy materials, fiberglass); fishing rods, titanium alloy glasses frames, bicycles

(2) Foam plastics with low density are often used as fillers in product packaging, which are shock-proof, easy to transport and low in price.

(3) The density of the "bricks" used to hit people in the movie is small. Tower cranes and desktop fan machines have high base density.

(4) The liquefied gas alarm is installed at the bottom and the natural gas alarm is installed at the top.

5. Identify substances. Real and fake gold and silver (fraud)

density and temperature

(1) At room temperature, blow up two balloons. Place them in the cold compartment of the refrigerator and near the fire. After a while, what will you notice?

The air expands in volume due to heating and becomes less dense and rises. After the hot air rises, the cold air above flows from all directions, forming wind.

in conclusion

Temperature can change the density of matter.

Thermal expansion and contraction of gas are the most significant, and its density is also most affected by temperature.

Thermal expansion and contraction of solids and liquids are not as obvious as those of gases, so the density is less affected by temperature.

Why is there a gap at the junction of rails?

Why do water pipes freeze and crack in winter?

Volume of 1kg water: V=m/ρ=1kg/1.0×103kg/m3 = =1.0×10-3m3

Volume of 1kg ice: V=m/ρ=1kg/0.9×103kg/m3 = 1.1×10-3m3

what have you found?

We found that the same mass of ice has a larger volume than water. Although ice is formed by condensation of water, due to their different temperatures, it can be seen that the volume of a certain mass of water becomes larger after condensing into ice. This shows that water does not simply follow the laws of "thermal expansion and contraction" of general substances.

abnormal expansion of water

Facts show that water at 4°C has the highest density.

When the temperature is higher than 4°C, the density becomes smaller and smaller as the temperature increases; when the temperature is lower than 4°C, the density becomes smaller and smaller as the temperature decreases. When water solidifies into ice, its volume increases and its density decreases. People call this characteristic of water the abnormal expansion of water.

Density and identifying substances

Example: The mass of a shot put is 4kg, and its volume is measured to be 0.57dm3. Is this shot put made of lead?

Analysis: To know whether the shot ball is made of lead, its density should be found first, and then compared with the density of metallic lead.

Tracking exercises

1. Why do water vapor and flames always go upward?

2. Where should the radiators for heating in northern residents’ homes be placed?

3. Observe the figure below and fill in the blanks: At 0 to 4°C, the density of water will ______ as the temperature increases, and ______ as the temperature decreases. We call this characteristic of water the ______ of water. Therefore, the density of water is maximum at ℃. When heating or cooling at this temperature, the density of water will be ______. Because ______ water has the highest density, in the cold winter, when the river surface freezes, the deeper river bottom can maintain ______ water temperature, and fish can still swim freely.

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Update Time: 2024-10-08

This template belongs to Physics courseware Lu Jiao edition eighth grade physics volume 1 industry PPT template

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