"Density" Quality and Density PPT Courseware 3

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"Density" Quality and Density PPT Courseware 3

1. The relationship between mass and volume of matter

Use a balance to weigh wooden blocks, aluminum blocks, and iron blocks with the same volume. Do they have the same mass? What revelations did you receive about the weighing results, and what questions can you ask?

What is the relationship between the mass and volume of objects of different materials?

What is the relationship between mass and volume of objects of the same material?

Experiment 1: Measure the mass of the same substance in different volumes.

Experiment 2: Measure the mass of the same substance whose volume is a multiple of the relationship.

Experiment 3: Measure the mass of different substances of the same volume.

analysis and argumentation

Experiments have proved that the ratio between the mass and volume of the same substance is certain, but the ratio between the mass and volume of different substances is different. Therefore, this ratio reflects a property of the substance.

In order to describe this characteristic of matter, we introduce the concept of density

one. Density: the mass per unit volume of a substance

Note: Density is a characteristic of matter that can usually be used to identify some substances. However, it will be affected by some external factors (such as temperature, pressure, state, etc.). When the temperature does not change much, since the thermal expansion and contraction of solids and liquids are not large, we can think that the density remains unchanged.

two. Density calculation formula:

Density = mass/volume

Density-ρ Mass-m Volume-V

Then the formula is: ρ =m/V

1. In general, different materials have different densities.

2. Materials with the same density are not necessarily the same kind of substances, such as kerosene and alcohol, ice and wax.

3. The same substance has different densities in different states. Like ice and water. When the state of an object changes, the mass does not change, because the volume changes, so the density changes. For example, when a piece of ice melts into water, its density changes from ______ to ______ but its mass does not change, so its volume becomes smaller.

4. Several issues that need attention

(1) Regarding the difference between the concepts of mass and density.

Mass is a property of an object, while density is a property of matter.

For example, if half of a bottle of gasoline is used, the mass of the remaining half is only half of the original, but the density remains unchanged.

The size of density is related to the type of substance and has nothing to do with the mass and volume of the substance.

six. Application of density formula:

1. Calculate the density of matter: ρ=m/V

Example: There is a commemorative coin for the 11th Asian Games. Its mass is 16.1g and its volume is 1.8dm3. Find the density of the metal that makes this commemorative coin. What kind of metal is it?

2. Calculate the volume of an object: V=m/ρ

Example: Use a balance to weigh the mass of a bundle of thin copper wires at 445 grams. It is known that the density of copper is 8.9×103 kg/m3. What is the volume of this bundle of thin copper wires?

Solution: Obtained from the formula ρ=m/v

v= m/ρ=445g/8.9g/cm3= 50cm3

Basic pass

1. According to the density formula ρ=m/V, which of the following statements is correct ( )

A． The density of an object is proportional to its mass

B. The density of an object is inversely proportional to its volume

C. The density of an object is directly proportional to its mass and inversely proportional to its volume

D. Density is a property of matter that has nothing to do with mass or volume

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Update Time: 2024-11-21

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

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