"Buoyancy" PPT courseware 3

Description

"Buoyancy" PPT courseware 3

learning target:

1. Know what buoyancy is and the causes of buoyancy.

2. Be able to use a spring dynamometer to measure the buoyancy force.

3. Know the factors related to the size of buoyancy.

1. Buoyancy:

1. Definition: An object immersed in a liquid (or gas) receives a vertical upward force from the liquid (or gas). This force is called buoyancy.

Object exerting force: liquid or gas

Direction: vertically upward (opposite to the direction of gravity)

Feedback exercise:

1. The force exerted on an object immersed in a liquid by the liquid is called buoyancy.

2. Make a diagram of the buoyancy force on the object in the figure below.

3. An egg is suspended in a container filled with salt water, and the container is placed on an incline, as shown in the figure. Several directions of forces are drawn on the picture. Do you think the direction of the buoyant force on the egg should be ( )

A. F1 B. F2

C. F3 D. F4

Example 1. A metal block is weighed in the air, and the spring dynamometer reads 27N. When it is immersed in water, the spring dynamometer reads 17N. What is the buoyant force it experiences, N?

Solution: F float = G - F pull =27N -17N =10N

Answer: The buoyant force it experiences is 10N.

Thoughts and Practice

There is an object hanging in the air under a spring balance with a reading of 4.9N. When it is placed in a liquid, it is found that the reading of the spring balance decreases by 2.5N. Then:

(1) What is the indication of the spring balance at this time? (2) What is the buoyant force on the object in the liquid?

3. Cause:

The difference in upward and downward pressure exerted by a liquid on an object.

That is: F float = F up - F down

Note: 1. When an object is buoyant, the upward pressure of the liquid on the object is always greater than the downward pressure of the liquid on the object.

think:

Does a liquid exert a buoyant force on everything immersed in it?

For example: a bridge pier is immersed in water to a depth of 25m. Does it receive buoyancy from the water?

4. Emphasis: The key to judging whether an object is buoyant is to see whether the lower surface of the object is subject to upward pressure from the liquid. If the object is tightly connected to the bottom of the container, the object is not buoyant (such as bridge piers, barrages). That is, the object is affected by the buoyancy force. F upward must exist, but downward F is dispensable.

Observation experiment:

⒈ Immerse the same object in the same liquid.

⒉ Are the readings of the two spring dynamometers the same? What are the differences?

⒊ What changes occur to the liquid level in the container?

⒋What did the experiment illustrate?

Experimental results:

The amount of buoyancy is related to the volume of liquid displaced by the object.

Summarize:

The buoyant force on an object immersed in a liquid is related to the density of the liquid and the volume of liquid displaced by the object. When an object is immersed in a liquid, the buoyant force it experiences has nothing to do with the depth of the object in the liquid.

Practice in class:

1. The side length of the cube is 10cm, and the upper surface is 20cm away from the water surface (g=10N/kg)

Find: ①The pressure of water on the upper surface ____, direction ______;

②The pressure of water on the lower surface ____, direction ______.

2. The side length of the cube is 10cm. The lower surface is subject to the upward pressure of 4000Pa by water, and the pressure is _____N. The pressure of water on the upper surface is ____ Pa, pressure ____N.

The buoyant force on the object is ____N. (g=10N/kg)

Keywords: buoyancy teaching courseware, New People's Education Edition eighth grade physics PPT courseware volume 2, eighth grade physics slide courseware download, buoyancy PPT courseware download, .ppt format

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Update Time: 2024-08-06

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

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