"Buoyancy" Buoyancy PPT

Description

"Buoyancy" Buoyancy PPT

Part One: Learning Objectives

1. Know that objects in water will be affected by buoyancy.

2. Know what causes buoyancy.

3. Be able to use the weighing method to determine the buoyancy force on an object.

4. Explore what factors are related to the size of buoyancy

Learning points

1. Causes of buoyancy.

2. Factors affecting the size of buoyancy.

Knowledge links: pressure, synthesis of force, equilibrium force, schematic diagram of force

Buoyancy PPT, part 2 content: independent preview before class

(Read textbook P49~P52, think about the following questions, draw relevant key contents in the textbook, and mark questions)

1. What is buoyancy?

2. Does the iron block sinking at the bottom of the water experience buoyancy? How to measure the buoyant force on an object immersed in a liquid?

3. What causes buoyancy?

4. What factors are related to the size of buoyancy?

Buoyancy PPT, Part 3: Classroom Cooperation and Exploration

1. Buoyancy

1. Thinking: As shown in Figure 1, do people floating on the Dead Sea experience buoyancy? _____. As shown in Figure 2, does the sinking iron block in the water experience buoyancy? _____.

2. (1) Experiment 1 (as shown below): Use a spring dynamometer to measure the gravity of the iron block in the air, G = _____, then immerse the iron block in water, and observe the spring dynamometer's indication F = _____.

Explanation: ① The object sinking in the liquid _____ (optional "receives" or "does not receive") buoyancy;

②The buoyancy force F on the iron block = _____.

(2) Summary: ①The object immersed in _____ is supported by _____, and this supporting force is called _____.

②The object exerting buoyancy is _____.

③The direction of buoyancy is _____.

④ Use a spring dynamometer to measure the gravity experienced by an object in the air as G. When the object is immersed in a certain liquid, the reading of the spring dynamometer is F. Then the buoyancy force experienced by the object in the liquid is F. Float = _____ .(Weighing method)

2. Causes of buoyancy

1. As shown in the figure, there is a cuboid immersed in a liquid with density ρ. The depth of the upper surface from the liquid surface is h1, and the depth of the lower surface from the liquid surface is h2.

(1) Are the front, back, left and right sides of the cuboid also under pressure from the liquid?

_____. Is there also a pressure difference between the left and right sides and the front and back sides? _____.

(2) Discussion 1: Analysis: Because the depth h1 of the upper surface from the water surface _____ the depth h2 of the lower surface from the water surface, the upper surface is subject to the pressure of water p1 _____ the lower surface is subject to the pressure of water p2, and because of the area of ​​the upper and lower surfaces of the cuboid They are equal, so the lower surface is subject to the vertical upward pressure F of the water upward _____ and the upper surface is subject to the vertical downward pressure F of the water downward. The direction of the resultant force is _____; F total = _____.

(3) Conclusion: ① The cause of buoyancy is ______________.

②F float = _____ (the direction of buoyancy is always _____).

Note: Buoyancy is the total effect of the liquid surrounding an object exerting pressure on the object from all directions. When performing force analysis on an object and considering the buoyancy force on the object, there is no need to consider some of the pressure exerted by the liquid on the object.

[Example 1] The gravity of a cylindrical wooden pile is 240 N. If a wooden pile is nailed vertically into the river bed, the volume of the wooden pile immersed in water is 0.02 m3, and the buoyant force on the wooden pile at this time is _____N.

2. Discussion 2: If the object is not completely immersed, then F float = _____.

3. Discussion 3: Put a piece of wax block into the beaker, let the wax block stick to the bottom of the beaker, add water,

Observe whether the wax block floats? Then move the wax block so that it is no longer close to the bottom of the beaker. Can it float? What does it mean?

Does not float; floats; it means that when the lower surface of the wax block is not subjected to upward pressure from water, there is no buoyancy.

3. Factors that determine the size of buoyancy

1. Is the buoyancy force related to the volume of the object immersed in the liquid?

Let the volume of the object immersed in the liquid in Figure 1 gradually increase, and it is found that the indication of the spring dynamometer gradually _____; Explanation: _______________________.

2. Is the buoyancy force related to the depth to which an object is submerged?

Let the object in Figure 2 stay at different depths below the liquid surface, and find that the spring dynamometer indicates _____; Explanation: _________________________.

3. Is the buoyancy force related to the density of the liquid?

Immerse the same object suspended on the spring dynamometer in clean water and salt water successively. Note down the readings of the spring dynamometer as F1 and F2 respectively. Find F1_____F2; explain_________________________.

Buoyancy PPT, Part 4: Homework

1. In the container, there are three objects A, B, and C. As shown in the figure, the parts of the objects in contact with the container wall are all sealed. When water is poured into a container, the object that does not experience buoyancy is ()

A. B. C

C. A D. Unable to judge

2. Which of the following objects does not experience buoyancy ()

A. Little ducks playing in the water B． Eagle flying in the blue sky

C. Whale swimming in the deep sea D. Bridge piers deep into the river bottom

3. As the diver gradually emerges from the water, the buoyant force on him ()

A. Gradually increase B. slowing shrieking

C. Always the same D. Increase first and then remain unchanged

4. A table tennis ball floats on the water. The object exerting the buoyant force on the table tennis ball is ()

A. Air B. pingpong

C. water d. water container

5. Slowly press the empty mineral water bottle into the water until it is completely submerged. In the following analysis of the buoyancy of mineral water bottles, which one is incorrect ()

A. The mineral water bottle is subject to the buoyancy of the water

B. The direction of buoyancy is vertically upward

C. The greater the volume of displaced water, the greater the buoyancy force it experiences.

D． After immersion, the deeper it is pressed, the greater the buoyancy force it will receive.

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Update Time: 2024-11-23

This template belongs to Physics courseware People's Education Edition Physics for Grade 8, Volume 2 industry PPT template

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