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

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

The first part: sorting out new knowledge

1. Density and temperature

1.The relationship between density and temperature

The density of substances is related to temperature. Most substances follow the law of "______", but water is special.

2. Thermal expansion and contraction and the formation of wind

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

3. Abnormal expansion of water

Water has the highest density at 4°C. When the temperature is higher than 4°C, water "expands with heat and contracts with cold"; when the temperature is lower than 4°C, water "shrinks with heat and expands with cold", which is called "abnormal expansion" of water.

In the cold winter, the river surface freezes, but the water in the deeper river bottom may maintain a temperature of 4°C, and fish can still swim freely in the water.

2. Density and material identification

1. The idea of ​​using density to identify substances: first find the density of the object based on known conditions, and then compare it with the density table to determine the type of material that makes up the object.

2. To identify substances with different densities (such as water and kerosene), you can use density or physical properties such as color and smell to identify them; to identify substances with the same density (such as alcohol and kerosene, ice and wax), you need to use color , smell, hardness and other physical properties to identify.

Density and Social Life PPT, Part 2: Application Examples

Type 1 Density and Temperature

Example 1: In order to explore the relationship between the volume and temperature of ice and water, a researcher heated 1 g of ice in a certain environment, recorded its temperature and volume respectively, and obtained the image shown in Figure 6-4-2. . Please observe this image and answer the following questions:

(1) When the temperature of ice rises from -4 ℃ to 0 ℃, the volume will ________ and the density will ________.

(2) When the temperature of water rises from 0 ℃ to 4 ℃, the volume will ________ and the density will ________.

(3) In winter, when the river surface freezes, the temperature of the river water in contact with the ice is______℃, and the temperature of the water at the deeper river bottom is________℃.

[Summary of rules]The density of matter is affected by temperature. Generally speaking, objects expand when heated and shrink when cooled, that is, the volume changes when the temperature changes. The density of a substance becomes smaller when the temperature increases and becomes larger when the temperature decreases (the exception is water, which has the highest density at 4°C) . In addition, when an object changes state, its volume will change, and the density of the substance will also change accordingly. Under normal circumstances, objects composed of the same material have the highest density in the solid state, followed by the liquid state, and the smallest density in the gaseous state (the exception is water, which is less dense in the solid state than the liquid state).

Type 2: Density and material identification

Example 2 A solid ball has a mass of 4 kg and a volume of 0.57 dm3. Is it made of pure lead?

[Method Guidance]How to identify substances: To identify which substance it is, you can find its density and then compare it with the density table.

Type 3: Other applications of density knowledge

Example 3 A copper ball has a mass of 178 g and a volume of 30 cm3.

(1) The ball is hollow, please write down the judgment process.

(2) Find the volume of the hollow part of this copper ball.

(3) After Xiaohua fills the hollow part of the ball with a certain liquid, the total mass is 314 g. Find the density of the filled liquid. (ρCopper=8.9×103 kg/m3)

[Method Guidance]Three methods to determine whether an object is hollow

There are generally three methods to determine whether an object is hollow: comparing density, comparing volume, and comparing mass. Take this question as an example:

① Compare the density: Find the density of the ball, ρ ball, ρ ball < ρ copper, then the ball is hollow;

② Compare the volume: Find the actual volume of copper V real, V sphere > V real, then the ball is hollow, V hollow = V sphere - V real;

③ Compare the masses: Assume that the ball is solid, find the mass of the solid ball m solid, m solid > m ball, then the ball is hollow.

Density and Social Life PPT, Part 3: Class Feedback

1. In the winter in the north, it is common to see outdoor water pipes covered with a layer of grass to prevent the water pipes from freezing and cracking. What causes water pipes to freeze and burst is ( )

A． When the water in the pipe freezes, it becomes denser

B． When water in pipes freezes, its volume increases

C. When water in a pipe freezes, its mass increases

D. The water pipe itself is not cold-resistant enough and breaks.

2. In production and life, people often use the density of materials as the main consideration in material selection, such as using aluminum alloys with lower density as the main material for aircraft shells. The following materials are mainly selected from the perspective of density ()

A． Plastic power outlet casing

B． Use plastic foam to make rolling "stones" in performance scenes

C. Using water as coolant for car engines

D. Making car tires from rubber

4. As shown in Figure 26-1, a lit candle will cause the pinwheel above it to rotate. This is because the flame of the candle increases the temperature of the nearby air, expands its volume, and changes the density of the air. The hot air ________ (optional "rise" or "fall") forms an airflow. The airflow flows through the paper pinwheel, driving the paper The windmill spins.

5. After water with a mass of 0.9 kg freezes into ice, its volume increases by 0.1 dm3. What is the density of the ice? What is the mass of ice?

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For more information about the PPT courseware "Quality and Density Density and Social Life", please click the Quality and Density ppt Density and Social Life ppt tag.

"Density and Social Life" Quality and Density PPT courseware download:

"Density and Social Life" Quality and Density PPT courseware download Part 1: Classification practice of knowledge points Knowledge point 1 Density and temperature 1. In the physics class, the teacher brought an alcohol lamp and a paper pinwheel, hung the paper pinwheel with a thin string and placed it above the lamp flame.

"Density and Social Life" Quality and Density PPT download:

"Density and Social Life" Quality and Density PPT Download Part One: Basic Knowledge Points Knowledge Point 1 Density and Temperature 1. Water has the characteristic of abnormal expansion. The picture shows the -t image of water with a mass of 1 g under standard atmospheric pressure. According to the image, it can be seen that the temperature is equal to 4..

"Density and Social Life" Quality and Density PPT:

"Density and Social Life" Quality and Density PPT Part One: Preview Perception 1. Density and Temperature 1. The relationship between the density and temperature of most substances. (1) The volume of a certain mass of gas after heating is ________, and the density is ________. (2)General gases, liquids and...

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Update Time: 2024-10-06

This template belongs to Physics courseware People's Education Edition Physics for Grade 8, Volume 1 industry PPT template

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