"Studying the Floating and Sinking Conditions of Objects" Buoyancy and Lift PPT Courseware 2

Description

"Studying the Floating and Sinking Conditions of Objects" Buoyancy and Lift PPT Courseware 2

learning target:

1. Through experiments, explore the floating and sinking conditions of objects;

2. Use the floating and sinking conditions of objects to explain the floating and sinking principles of submarines and balloons and the salvage method of buoys.

What are the conditions for objects to float and sink?

The submarine sometimes surfaces and sometimes dives into the water. What is the secret? We study it experimentally.

Activity Make the egg float and sink like a submarine

experiment equipment:

Cup, concentrated brine, salt, eggs, mixer

Discussion and Thoughts:

1. What two forces act on the egg in salt water?

2. Which force changes due to the different states of the egg?

1. Floating and sinking conditions of objects:

(1) Objects immersed in liquid

F float>G object: float → finally float

F floating < G object: sinking → finally sinking to the bottom

F float = G object: suspended (can be stopped at any depth)

(2) Objects on the floating liquid: F floating _____ G objects

The floating and sinking conditions of objects

(1) Float F float=G V dischargeρ matter

(2) Suspension F float=G V discharge=V matter ∴ρ liquid=ρ matter

(3) Float F float>G V discharge=V substance ∴ρ liquid>ρ substance

(4) Sinking F float

ρ is the density (average density) of an object, not the density of the matter that makes up the object

The floating and sinking of an object immersed in a liquid is determined by the combined force of buoyancy and gravity.

Classroom Thoughts What are the similarities and differences between floating and levitation?

Common points:

Stand still under the influence of a balancing force.

For objects floating and suspended in a liquid surface, the buoyancy force is equal to gravity.

difference:

Floating is when part of an object is immersed in a liquid, and levitation is when the entire object is immersed in a liquid.

Think about what are the ways to change the floating and sinking of objects?

Change its own gravity.

Change its own volume or change the density of the liquid to change the buoyancy.

2. Technical application of floating and sinking conditions

1. Ship

(1) Working principle: It works on the principle that objects float on the water.

(2) Use steel that is denser than water to make it hollow so that it can displace more water and increase the available buoyancy.

(3) The ship is a floating body in the river and the sea, so it is subject to the same buoyancy force. According to Archimedes' principle, its immersed volume in sea water is smaller than that in river water.

2. Submarine

——Use the method of water absorption and drainage to change the gravity of the submarine to achieve floating and descending.

1. Working principle: The submarine floats, dives and levitates by changing its own gravity.

2. The change of the submarine's dead weight depends on how much water is filled or discharged in the water tank.

Process and principle:

① Process: No matter whether the submarine sinks or floats under the water, the buoyancy force it receives remains unchanged. When the water tank is filled with water, F float < G and the submarine sinks. When F float = G, the submarine floats. When water is drained, when F float > G, the submarine floats.

②Principle: The buoyancy remains unchanged after being immersed in water, and the ups and downs are achieved by changing its own gravity (filling or draining the water tank)

Knowledge platform

What balloons and airships have in common

(1) Balloons and airships are filled with gases that are less dense than air - hydrogen, helium, hot air, etc.

(2) Principle: Utilize the buoyancy of air to achieve rising and falling by changing its own volume.

density meter

Purpose: An instrument that can directly measure the density of liquids.

Reading method: the scale facing the liquid level at rest multiplied by the density of water

Scale characteristics: small at the top and large at the bottom, uneven intervals between scales.

Working principle: It is made by using the principle that buoyancy is equal to gravity when an object floats on the liquid surface.

Consolidation training:

1. Which of the following statements is correct ( )

A. The object is affected by the buoyancy force when it floats up, but is not affected by the buoyancy force when it sinks.

B. Whether the ship is sailing on the sea or stationary at the dock, it is subject to the buoyancy of the water.

C. The gas density in the hot air balloon is greater than the density of air, so the ball is not affected by buoyancy when it lifts off.

D. The submarine is not affected by buoyancy when diving in the depth of 150m.

2. A stone weighs 5N. Hang the stone on the lower end of the spring dynamometer and immerse it in a certain liquid. At this time, the spring dynamometer indicates 2N. Then the buoyancy force of the stone on the liquid is_ _N. The direction of the buoyancy force is _____, and the object exerting the force is __________. When the stone sinks in the liquid, the buoyancy force will be _____ (fill in "received" or "not received").

3. During World War II, a German Nazi submarine hit the bottom of the sea and was stranded during its dive. The reason was that it could not float ( )

A. There is buoyancy, but the buoyancy is less than gravity

B. There is buoyancy, and the buoyancy is equal to gravity

C. There is no water entering the bottom of the submarine and it cannot generate buoyancy.

D. The machine is broken and does not produce buoyancy.

practise:

1. A wooden block weighing 10N floats up in the water, and finally floats on the water. The buoyant force on the wooden block is ( )

A. Less than 10N when floating, more than 10N when floating

B. Greater than 10N when floating, less than 10N when floating

C. It is equal to 10N when floating and equal to 10N when floating.

D. Greater than 10N when floating, equal to 10N when floating

2. When a solid wooden ball and a solid iron ball of the same mass are immersed in water and let go, the wooden ball floats up and the iron ball sinks. The magnitude of the buoyant force they experience when they are at rest is ( )

A. F wooden ball > F iron ball B. F wooden ball < F iron ball

C. F wooden ball = F iron ball D. Unable to judge

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"Studying the Floating and Sinking Conditions of Objects" Buoyancy and Lift PPT Courseware:

"Studying the Floating and Sinking Conditions of Objects" Buoyancy and Lift PPT courseware Review the past and learn new things 1. What factors are related to the size of buoyancy? Liquid, V displacement 2. What is the relationship between the size of buoyancy and the weight of liquid displaced by an object? F float = G row 3. How to calculate the gravity of an object? G=mg=gV 4..

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Update Time: 2024-10-22

This template belongs to Physics courseware Guangdong and Shanghai version of eighth grade physics volume 2 industry PPT template

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