"Understanding Buoyancy" Buoyancy and Lift PPT Courseware 2

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"Understanding Buoyancy" Buoyancy and Lift PPT Courseware 2

1. What is buoyancy?

Activity 1: Compare the gravity of a metal block in air and water

Design experiment: As shown in the figure, use a spring dynamometer, a block, a thin wire, a beaker, water and other equipment to compare the readings of the spring dynamometer when the block is in air and water.

step:

(1) Determine the gravity of the object in air.

(2) Immerse the block in water and weigh its gravity.

think:

Comparing the two measurement results, you can find that the metal block is ___ in water than in air.

Why?

It is concluded that the spring dynamometer shows _____ because the block is subjected to the vertical upward ____ force of the liquid.

Buoyancy (F float)

1. Definition: An object immersed in a liquid is supported vertically upward by the liquid.

2. Object exerting force: _______ 3. Direction: ___________

think:

4. In gas: _____ (received?) buoyancy

5. Measuring buoyancy by weighing method (i.e. the method in Activity 1):

The size of the buoyancy force is equal to the difference between the two readings of the spring dynamometer.

F float =________

Example 1. An iron block is hung on a spring scale. When weighed in air, the reading of the spring scale is 32 N. When the whole thing was immersed in water and weighed, the reading was 12 Newtons. What is the buoyant force on the iron block?

Example 2: An aluminum block with a mass of 5 kg is suspended by a spring balance. When it is placed in alcohol, the reading of the spring balance is 30 N. Find the buoyancy force of alcohol on the aluminum block?

Think about it:

1. Are the bridge piers subject to buoyancy?

2. What causes buoyancy?

2. How is buoyancy generated?

Activity 2 Discuss the causes of buoyancy

As shown in Figure 9-3, if a cuboid is taken as the research object in water, please use the characteristics of liquid pressure to discuss

Causes of buoyancy

(1) The corresponding parts of the left and right sides of the cuboid have the same depth in the water, so the pressure is the same. And because the side areas are the same, the pressure on the two sides of the cuboid is the same, but in opposite directions, and the effects of the forces cancel each other out.

(2) Similarly: What is the pressure on the front and back sides of the cuboid?

(3) Analyze and compare the pressure of water on the upper and lower surfaces of the cuboid?

Buoyancy is caused by the difference in the upward and downward pressure of a liquid on an object.

Buoyancy size expression:

F float = F up - F down

Buoyancy direction: vertically upward

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

conduct experiment

(1) In the process from position 1 → 2 → 3, the buoyant force on the iron block is _________.

(2) In the process of moving from position 3 → 4, the buoyancy force on the iron block is ________.

(3) Immerse the iron block in clean water and concentrated salt water in sequence. The iron block will experience greater buoyancy in _________.

get conclusion

The buoyancy force on an object immersed in a liquid depends on the volume of the object immersed in the liquid and the density of the liquid. The buoyant force on all objects immersed in the same liquid depends on the depth of the object immersed in the liquid. .

Class exercises:

1. In the debate between the big fish and the small fish shown in the picture below, the ________ fish’s statement is correct and the ________ fish’s statement is incorrect. This is because when two fish are immersed in the same liquid, the buoyancy force they experience is related to _________ and has nothing to do with _________.

2. In the experiment as shown in the figure, the iron block is immersed in water, and the distance between the bottom surface of the iron block and the water surface is h, then the relationship between the buoyancy force F of the water on the iron block and h should be:

When the iron block enters the water from the water surface, as h increases, F floats ________;

When all the iron blocks are immersed in water, as h increases, F floats _________.

3. Which of the following statements is correct ( )

A. Objects floating on the liquid surface are subject to buoyancy, while objects sinking are not subject to buoyancy.

B. Objects floating on the liquid surface experience a large buoyancy force, while sinking objects experience a small buoyancy force.

C. Any object that sinks to the bottom of a liquid is not buoyant.

D. None of the above statements are correct

4. As shown in the figure. This is a diagram of the experimental device for studying the magnitude of buoyancy. Please answer the following questions based on the picture:

(1) In pictures b and c, the spring dynamometer has different indications, indicating that the buoyancy force on an object immersed in the same liquid is related to _________.

(2) In Figures c and d, the spring dynamometer has different indications, indicating that when an object displaces the same volume of liquid, the buoyancy force it experiences is related to _________.

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Update Time: 2024-07-07

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