"Floating and sinking conditions and applications of objects" Buoyancy PPT

Description

"Floating and sinking conditions and applications of objects" Buoyancy PPT

Part One: Learning Objective Navigation

learning target

1. Understand the floating and sinking conditions of objects and be able to use them to solve practical problems.

2. Understand the principles of floating and sinking of ships, balloons, motorboats and submarines

Learning points

Floating and sinking conditions of objects and their applications.

Knowledge links: Effects of force, Archimedes' principle

PPT on the floating and sinking conditions of objects and their applications, part 2: independent preview before class

(Read textbook P57~P59, think about the following questions, draw relevant key contents in the textbook, and mark questions)

1. How many forces act on an object immersed in water that is not in contact with the bottom of the container? What are the differences?

2. When an object immersed in a liquid floats, suspends, or sinks, what is the relationship between the buoyancy force and gravity exerted on the object? What is the relationship between the density of objects and the density of liquids?

3. Why can ships made of steel float on the water and even carry cargo?

4． What is displacement? What are its units?

5. How does a submarine dive and surface?

6. Why can balloons and airships float in the air? Can you make a hot air balloon? Try to do it.

PPT on the floating and sinking conditions of objects and their application, part three: classroom cooperation and exploration

1. Floating and sinking conditions of objects

Tip 1. A suspended object completely enters the liquid and can rest anywhere inside the liquid. Its volume is equal to the volume of the liquid displaced by the object; while floating is when the object rests on the surface of the liquid and its volume is greater than the volume of the liquid displaced by the object. ．

Discussion 1: When an object is immersed in a liquid, F float = ρ liquid V discharge g, G object = ρ object V object g, and since V discharge = V object, the floating and sinking conditions of the object can also be written as:

When an object floats, F floats ___ G object, so ρ liquid ___ ρ object;

When an object is suspended, F float ___ G object, so ρ liquid ___ ρ object;

When an object sinks, F floats ___ G object, so ρ liquid ___ ρ object.

Tip 2. Understanding of floating and sinking conditions:

① Do not mistakenly believe that floating objects receive greater buoyancy, while sinking objects receive less buoyancy. This is because the floating and sinking of an object is determined by the relationship between the object's gravity and the buoyancy force it experiences (or in other words, it is determined by the relationship between the object's density and the density of the liquid), and the buoyancy force experienced by the object is determined by the gravity of the liquid it displaces.

②Comparison between suspension and floating:

Similar points: F float = G object.

Differences: suspension: ρ liquid = ρ substance, V row = V substance; floating: ρ liquid > ρ substance, V row < V substance.

[Example 1] Immerse a small wooden block and a large stone in water, and release your hands at the same time. If the small wooden block floats up and the big stone sinks, the one with the greater buoyant force is ()

A． Small wooden block B. big Stone

C. Same size D. unconfirmed

[Example 2] When a table tennis ball is completely submerged in water, the change in its buoyancy from motion to rest after letting go is ()

A． The buoyancy force continues to increase, but is less than gravity

B． The buoyancy force remains unchanged, but the buoyancy force is greater than gravity

C. The buoyancy force remains unchanged at first, then becomes smaller but is always greater than gravity. Until finally, when it is at rest, the buoyancy force is equal to gravity.

D． The buoyancy force is first greater than gravity and then less than gravity

[Example 3] An object with uniform mass is suspended in water. If one third of it is cut off, it will ()

A． Floating B. sink

C. Suspension D. All of the above are possible

2. Application of floating and sinking conditions of objects

1. Discussion 2: When a ship goes from the river to the sea, will it float or sink?

Analysis: The ship was in the ____ state both times. The buoyancy force it experienced was ____ its own weight. The buoyancy force it experienced twice was ____. Since the density of sea water is greater than the density of river water, the volume of sea water it displaced ___ _The volume of water it displaces in the river is larger than that of a ship.

2. Discussion 3: The submarine is suspended in the water. When the water tank is filled with water, the mass of the submarine becomes ____ and will ____ (optional "float" or "sink"); when compressed air is used to remove the water in the water tank When a part of it is discharged, the mass of the submarine becomes ____ and it will ____ (optional "floating" or "sinking"). Before it emerges from the water, the buoyancy force experienced by the submarine will ____(optional "get bigger", "get smaller" or "unchanged").

3. Balloons and airships use the ____ of air to lift off. The balloon is filled with gas with a density equal to that of air, such as hydrogen, helium or hot air.

Tip 4: Calculate buoyancy method:

(1) Weighing method: F float =____ (use a spring dynamometer to measure buoyancy).

(2) Pressure difference method: F float =____ (use the cause of buoyancy to find the buoyancy).

(3) When floating or suspended, F float =____ (calculate buoyancy based on the balance of two forces).

(4) F float = ____ or F float = ____ (Archimedes’ principle).

Tip 5: Compare the buoyancy:

(1) If the masses of several objects are equal (or the same object), the buoyancy is often compared based on the floating and sinking conditions;

(2) If several objects have equal volumes and are immersed in the same liquid, Archimedes' principle is often used to compare the buoyancy forces.

PPT on the floating and sinking conditions and application of objects, part 4: homework after class

1. Among the following equipment and equipment, the one that utilizes buoyancy is ()

A． Water pump B． barometer

C. Submarine D. plumb line

2. In the water, the positions of fish, floating wood, and stones resting on the bottom of the water are as shown in the picture. The following statements are correct ()

A． Water exerts less pressure on stone than on wood

B． The buoyant force on the wood is greater than its own weight

C. The buoyant force on the fish is equal to the weight of the water it displaces

D． The buoyant force on the stone is equal to its own gravity

3. As shown in the figure, a and b are images of the relationship between the mass and volume of two substances. Two solid objects A and B with equal volumes are made of two substances a and b respectively. They are immersed in water and let go after stabilization ()

A． B floats, and the buoyant force on B is small.

B． A floats, the buoyant force on A is greater

C. B sinks, A is subject to greater buoyancy

D． A sinks, B experiences a greater buoyant force

4． If three balls A, B, and C with equal volumes are immersed in the liquid as shown in the figure, then the buoyancy force on them satisfies ()

A． FA＞FB＞FC

B． FA＜FB＜FC

C. FA＝FB＝FC

D． I don’t know what material the ball is made of, so I can’t tell.

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Update Time: 2024-10-21

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