"The Floating and Sinking of Objects" Buoyancy PPT Courseware

Description

"The Floating and Sinking of Objects" Buoyancy PPT Courseware

learning target

1. Know the floating and sinking conditions of objects;

2. Understand the application of physical knowledge in production, life and society through the practical application of floating and sinking conditions;

3. Know the principles of density meters, salt water seed selection, submarines, and hot air balloons.

The mysterious "Dead Sea"

In western Asia, at the junction of Palestine and Jordan, there is a "Dead Sea". Legend has it that about two thousand years ago, the Roman commander Dido marched into Jerusalem, attacked the Dead Sea, and ordered the execution of captured slaves. The slaves were thrown into the Dead Sea. They did not sink into the water and drown, but were carried back to the shore by the waves. Didu was furious and once again ordered the prisoners to be thrown into the sea, but the slaves remained unharmed. Didu was horrified, thinking that the slaves were blessed by the gods and survived repeated drowning, so he had to order them all to be released.

Explore the floating and sinking conditions of objects

We can analyze the stress on an object immersed in liquid and design the experiment as shown below to verify it.

in conclusion:

1. The sinking and floating of an object in a liquid depends on the _____ force and the magnitude of the _____ force on the object. That is, by changing the magnitude of gravity or buoyancy, the floating or sinking state of an object can be changed.

2. When F float>G, the object floats up

When F floats < G, the object sinks

When F float = G, the object is in a suspended or floating state

Two processes:

F float＜G object F float＞G object

Object sinks Object floats

Three states:

F float = G object F float = G object F float < G object

Object floats Object levitates Object sinks to the bottom

Think about it:

Submerge the copper block and the wooden block in the water. The copper block sinks to the bottom and the wooden block floats on the water. By consulting the density table, you find out what is the relationship between the density of the copper block, the density of water, and the density of the wood block?

So, can we compare the density of an object with the density of a liquid to determine whether an object floats, sinks, floats or floats in a certain liquid?

float: sink:

F float > G F float < G

ρ liquid gV row>ρ material gV material ρ liquid gV row<ρ material gV material

∵V row=V thing ∵V row=V thing

∴ρ liquid>ρ substance ∴ρ liquid<ρ substance

levitate: float:

F float = G F float = G

ρ liquid gV row = ρ substance gV substance ρ liquid gV row = ρ substance gV substance

∵V row=V object ∵V row

∴ρ liquid=ρ object ∴ρ liquid>ρ object

Floating and sinking conditions

(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

Simply put, the floating or sinking of an object immersed in a liquid depends on the combined force of buoyancy and gravity. You can also change the floating and sinking state of an object by changing the density of the liquid and object.

What is the difference between levitation and floating?

Suspended objects are fully immersed; floating objects are partially immersed.

Application of floating and sinking conditions

(1) Density meter

1.What kind of instrument is a density meter?

What are the characteristics of its scale?

An instrument for measuring the density of liquids, the scale is on

Small and big at the bottom, sparse at the top and dense at the bottom.

2. What is the working principle of density meter?

The condition for an object to float on the liquid surface F float = G

3. The deeper the density meter is immersed in the liquid, the greater or the smaller the density of the liquid?

The smaller

(2) Salt water seed selection

Which seeds are better, those that sink to the bottom or those that surface? Why?

(4) Hot air balloon

The lifting and lowering of a hot air balloon is a relatively complex process, which is related to the volume of the hot air balloon and the density changes of the gas inside the hot air balloon. When the huge air bag of the hot air balloon is filled with air (ignoring the volume change), the air in the air bag is heated with a nozzle. The temperature of the gas inside the hot air balloon increases and the density decreases. When the density of the gas inside the hot air balloon is less than the density of the gas outside it, the hot air balloon rises.

Class exercises

1. The iron nail sinks in the water because of the buoyancy force _gravity. During the process of complete sinking, the buoyancy force on the iron nail is _____. (Please choose "get bigger", "get smaller" or "unchange")

2. When a ball floating on the water is slowly pressed into the water with your hands, the buoyancy force on the ball will be ___ and the pressure exerted on it will be ___. (Choose "get bigger", "get smaller" or "no change")

3. The relationship between the buoyancy force and gravity of an object suspended in a liquid is F _____G object. So what is the relationship between the density of the liquid and the density of the object? ρ liquid _____ ρ matter. (Choose "greater than", "equal to" or "less than")

4. Three solid balls A, B, and C with equal masses are placed in a certain liquid and are at rest as shown in the figure. The relationship between the buoyancy forces F A, F B, and F C they experience should be: F A ＿＿F B ＿＿F C; The relationship between their densities ρ A, ρ B, and ρ C is: ρ A ＿＿ρ B ＿＿ρ C. (Please fill in “＞”, “＜” or “=")

5. When three pieces of metal, copper, iron, and aluminum, with the same mass, are put into mercury, the buoyant forces they receive are F1, F2, and F3 respectively. The relationship between the magnitude of these three forces is ( )

A. F1>F2>F3 B. F1＝F2＝F3

C. F1＜F2＜F3 D. Unable to determine

6. The density meter is an instrument used to measure __________. If the same density meter is placed in two liquids A and B and both are stationary, then the buoyancy force F A _ F B suffered by the density meter in the two liquids. The densities of the two liquids are ρA and ρB. (Please fill in “＞”, “＜” or “=")

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For more information about the "Floating and Sinking of Buoyant Objects" PPT courseware, please click on the "Floating and Sinking of Buoyant Objects" PPT courseware.

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Update Time: 2024-07-10

This template belongs to Physics courseware Shanghai Science Edition 8th Grade Physics industry PPT template

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