The work was carried out by a physics teacher of the first category of the Municipal Educational Institution “OSOSH No. 3”, Ocher, Perm Territory
Bavkun Tatiana Nikolaevna
- Why does a button or nail sink in water, but large ships float on the surface of the water?
- Historical reference.
- Formulation of the law.
- Mathematical expression of this law.
- Experiments confirming the validity of the law.
- The method of practical use of the law.
Archimedes (287–212 BC) - the greatest ancient Greek scientist and inventor. He invented the Archimedean screw and determined the composition of an alloy by weighing in water. He established the rule of leverage and discovered the law of hydrostatics.
Continuation of historical information:
There is a legend about how Archimedes came to the discovery that the buoyant force is equal to the weight of the liquid in the volume of the body. He reflected on the task given to him by the Syracusan king Hieron (250 BC). Archimedes was instructed to find out, without breaking the crown, whether there were impurities in it. And then one day......
Eureka! Eureka!
I found!
Continuation of historical information
When solving this problem, Archimedes came to the conclusion: bodies that are heavier than the liquid, being lowered into it, sink deeper and deeper until they reach the bottom, and, while in the liquid, lose as much weight as the liquid weighs, taken in the volume of the bodies.
Having lifted the body, place a casting vessel under it, filled with liquid to the level of the casting tube.
The entire body is immersed in liquid. Wherein part of the liquid, the volume of which is equal to the volume of the body, is poured out from the pouring vessel into the glass.
The spring pointer rises, indicating a decrease in body weight in the fluid.
Continuation of the experimental justification:
If you pour liquid from a glass into a bucket, the liquid that was displaced by the body, then the spring pointer will return to its initial position.
Based on experience, it can be concluded that The force pushing out a body completely immersed in a liquid is equal to the weight of the liquid in the volume of this body.
Archimedes' law.
“A body immersed in a liquid is subject to a buoyancy force equal to the weight of the liquid displaced by this body.”
This law shows the relationship between the density of the liquid g and the volume of that part of the body that is immersed in the fluid V of the body, a relationship in the form of direct proportionality.
F A = P f = g m f = g g f V body
1. Swimming bodies:
If the force of gravity F is less than the Archimedean force F A.
Swimming bodies: The body floats on the surface of the liquid or floats up.
2. Floating bodies:
If the force of gravity F is equal to the Archimedean force F A .
A body is in equilibrium anywhere in a liquid or floating in a liquid.
3. Floating bodies:
The body sinks to the bottom or drowns.
If the force of gravity F is greater than the Archimedean force F A.
5. Sailing of ships:
Lesson topic: Floating bodies
- Lesson topic: Floating bodies
- The purpose of the lesson: to instill the skills of applying theory to practice using the example of making a raft for crossing from improvised means.
- Equipment: multimedia projector, blanks for making a raft, a vessel with water, viburnum fruits, 2 sheets of aluminum foil, salt, potatoes.
- Lesson progress: 1.Repetition of Archimedes' law and the conditions for floating bodies.
- 2.Explain to students what they need to know and have to make a raft
- 3. Calculation of the parameters necessary for the manufacture of the raft.
- 4. Making a raft and testing it for example of buoyancy.
- 1.Children, let's remember Archimedes' law. Asya you want.
- Let's.
- Asya: When immersed in a liquid or gas, a buoyant force acts vertically upward, numerically equal to the weight of the displaced liquid or gas. These are the forces in the picture
- Who will write this statement mathematically? Do you want Tanzil? Let's.
- Tanzilya writes Archimedes' law on the board:
- Fa=ρлgV
- Okay, sit down.
- Now looking at the formula, tell me what does the Archimedean force depend on? Mariam.
- Mariyam - From the formula it is clear that the greater the Archimedean force, the greater the density of the liquid and the volume of the body. The figure shows how the Archimedean force increases with the density of the liquid.
- Gasoline water mercury
- Thank you, sit down.
- Now tell me the condition for floating bodies.
- Elvira - the equality of the Archimedes force and the force of gravity of the body is the condition for the body to float. A body located inside a liquid is acted upon by two forces: the force of gravity (Ft) directed vertically downward, and the Archimedean force directed upward (Fa).
- Okay, Elvira, sit down.
- Zulfiya write down what was said on the board.
- Zulfiya writes:
- Fa= Ft
- The force pushing out a body completely immersed in a liquid (gas) is equal to the weight of the liquid (gas) in the volume of this body.
- ρлgV=mg
- Any body floats in water because the weight of water displaced by the underwater part of the body is equal to the weight of the body with the load in the air or the force of gravity acting on the body with the load.
- Okay, now let's move on to the calculations, you will actively help me.
- And so we must use our knowledge to build a raft that will lift a person. We will measure the person's weight. We will take the tin soldier as a person. The material for the raft will be wooden slats, from which we will knit the raft. To do this, we must know how many slats we should take. And so we begin. The lifting force of a raft is the difference between the force of Archimedes and the weight of the raft itself. The lifting force must be equal to the weight of the soldier.
- Fa-mg=Fп
- Fa=ρлgV
- m= ρсV
- V=NV0
- Fп= ρв gNV0- ρс gNV0
- Fп=g NV0(ρв- - ρс) , hence we have
- If the cross-section is square and the side is 1 cm with the length of the rail
- 20 cm, then its volume will be V0 =2*10-5 m3.
- From here we find the number of slats:
- N=0.5*105 m3. A tin soldier weighs 0.5 N. According to these data Let's calculate N. We get N=5 Now we know how many slats we need. Let Mariam and Zulfiya assemble the raft, take the slats and tie them with rope.
- While they assemble the raft, let's demonstrate a few experiments and let the rest answer questions.
- 1.Experience with potatoes:
- Elvira demonstrates:
- There are potatoes in two vessels, water at your disposal, and something else after which the potatoes will float. Tell us what it is and we'll make sure the potatoes float. Experiment:
- put potatoes in a glass and add liquid
- Why do potatoes float?
- Experiment:
- put potatoes in a glass and add liquid
- Why do potatoes float?
- We dissolved the salt, and the density of the water became greater than the density of the potato and it floated up.
- Okay, that's right Asiyat
- 2. Experience with viburnum fruit. Asiyat demonstrates. I throw a viburnum fruit into a glass of fresh sparkling water. It is slightly heavier than the water it displaces and will sink to the bottom. But soon the viburnum fruit floats up. Look carefully at the viburnum fruit and answer why the viburnum fruit floated up?
- Air bubbles stick to the viburnum fruit and they lift it up like pontoons, at the top the bubbles burst and it falls down and so on. This is how a submarine floats up.
- That's right, well done Tanzilya.
- 3.Tanzilya will demonstrate the experience with the boat.
- Look, from two identical foils, I make a boat and a ball from this foil and lower them into the water.
- As you can see, the boat floats, but a ball of the same weight sinks. Explain.
- The raft with the soldier does not sink. Now you have convinced yourself, and your labors were not in vain.
- Let's now find out which tree is best to take for the raft.
- Mariam: from the formula
- Fп =g NV0(ρл- ρд)
- It is clearly seen that the lifting force will be greater, the lower the density of the tree. Therefore, it is advisable to take dry slats and wood with a lower density.
- So we all practically applied our knowledge to calculate the parameters of the raft. Thanks to all participants.
- D/Z § 50, questions
- Come up with a simple experiment in which you could compare the density of paraffin or an eraser with the density of water. Try this experiment and rewrite the output below by filling in the blanks.
- The density of paraffin...the density of water, since...
- The density of an eraser is... the density of water, since...
- Textbook f-7 Peryshkin
- CDs open physics, BENP, BNP
- Tulchinsky Qualitative problems in physics
- Perlman entertaining physics
- Physics teacher, Municipal Educational Institution Secondary School, Karasu village
- Aliev H.H.
Objectives: To familiarize schoolchildren with the phenomenon of floating bodies in liquid, to study the conditions for floating bodies based on studying the concept of buoyancy force. Develop the ability to apply knowledge in specific learning situations and explain the reasons: why bodies float in some liquids and sink in others. The ability to think logically and develop creative activity. Cultivate a conscientious attitude towards learning, a desire to learn new things and positive motivation for learning, and communication skills.
Frontal survey 1. What phenomena do you know that indicate the existence of a buoyant force? 2.What experience do you know that can be used to determine the value of Archimedean force? 3. Is the buoyant force with which the liquid acts on a steel ball and a steel plate of the same mass immersed in it the same? 4.Why do some bodies float and others sink? Why does a nail sink in water, but a huge ship floats?
Problem A piece of marble with a volume of 0.1 m³ must be lifted from the bottom of the lake. What force will be needed for this if the mass of the piece is 300 kg? Given: m=300 kg ρ w =1000 kg/m³ g=10 N/kg V t =0.1 m³ _______________ F-? Solution F A = ρ f g V t F A = 1000 kg/m³·10 N/kg·0.1 m³ = 1000 N; F t =m g F t = 300 kg·10 N/kg = 3000 N; F = F t - F A F = 3000 N N = 2000 N. Answer: 2 kN Problem (solution on the board)
A body floats if... A body is in equilibrium if... A body sinks if... Explain the position of the bodies in these cases? Continue the sentence. Question Question 6.
F A F t > F A 2. The force of gravity directed downward is less than the buoyant force "title=" Consider three cases: 1. The force of gravity directed downward is greater than the buoyant force directed upward. In this case, the resulting force is directed downward and the body sinks. F t > F A F t > F A 2. The downward force of gravity is less than the buoyant force" class="link_thumb"> 9 !} Let's consider three cases: 1. The force of gravity directed downward is greater than the buoyant force directed upward. In this case, the resulting force is directed downward and the body sinks. F t > F A F t > F A 2. The force of gravity directed downward is less than the buoyant force directed upward. In this case, the resulting force is directed upward, and the body floats up. F t F A F t > F A 2. The force of gravity directed downward is less than the buoyant force "> F A F t > F A 2. The force of gravity directed downward is less than the buoyant force directed upward. In this case, the resulting force is directed upward, and the body floats up. F t F A F t > F A 2. The force of gravity directed downward is less than the buoyant force "title=" Consider three cases: 1. The force of gravity directed downward is greater than the buoyant force directed upward. In this case, the resultant force is directed downward and the body sinks. F t > F A F t > F A 2. The force of gravity directed downward is less than the buoyant force"> title="Let's consider three cases: 1. The force of gravity directed downward is greater than the buoyant force directed upward. In this case, the resulting force is directed downward and the body sinks. F t > F A F t > F A 2. The force of gravity directed downwards is less than the buoyant force">!}
Density of water, kg/m 3 Density of substance, kg/m 3 sinks or does not sink Physical experiment Finding out the conditions for floating bodies in liquid Instruments and materials: A glass of water, steel, aluminum, brass, wood, cork and paraffin cylinders Task 1. Lower into the water one by one body: steel, aluminum, brass, wood, cork and paraffin cylinder. Find out which ones sink and which ones float. 2. Write down the results of your observations in the table: Study the table and draw a conclusion: under what conditions do bodies sink in water?
Conclusions: 1. A body sinks if the average density of the body ρ avg exceeds the density of the liquid ρ l: 2. The body floats up if the average density of the body ρ avg is less than the density of the liquid ρ l: 3. The body floats at an arbitrary depth if the average density of the body is ρ avg equal to the fluid density ρ l: ρ avg > ρ l ρ avg ρ l ρ avg 
One of these works of Archimedes is the essay “On Floating Bodies”. The manuscript of this translation was discovered in 1884 in the Vatican Library in a Latin translation. The Greek text was found only in 1905. At the same time, about three-quarters of the text of the Archimedes manuscript was preserved.
The average density of living organisms inhabiting the aquatic environment differs little from the density of water, so their weight is almost completely balanced by the Archimedean force. Thanks to this, aquatic animals do not need strong and massive skeletons. For the same reason, the trunks of aquatic plants are elastic. This is interesting
The swim bladder of a fish easily changes its volume. When a fish, with the help of muscles, descends to a greater depth and the water pressure on it increases, the bubble contracts, the volume of the fish’s body decreases and it swims in the depths. When rising, the swim bladder and volume of the fish increases and it floats to the surface. This is how the fish regulates the depth of its dive. Swim bladder of a fish This is interesting
Place a chicken egg in a jar of tap water. The egg has sunk and is at the bottom of the jar. Add a few tablespoons of table salt to a jar of water and the egg will begin to float. Why is this happening? The condition for the navigation of ships is the equality of the force of gravity and the buoyant force of Archimedes acting on the ship. The floating condition is violated if the density of the liquid changes (the density of the liquid in the jar will increase, the Archimedes force will increase, and it will float on the surface).
24 Reflection (card for each student) How did I feel during the lesson? Draw a smiley face at a depth that would correspond to the depth of your immersion in today's lesson. Reflection (card for each student). Summing up the lesson. Grading.
Resources used: for your attention! Author: physics and computer science teacher Z.V. Aleksandrova, Municipal Educational Institution Secondary School 5 Pechenga, Murmansk region, 2009
Presentation for a lesson on the topic “Floating bodies” Suchkova E.V., physics teacher at secondary school “MOU” town. Kozhva, Pechora SWIMMING BODIES Under water, an iron whale, Day and night the whale does not sleep, Day and night under water, Protects your peace. 1 Conditions for floating bodies BEHAVIOR OF THE BODY RELATIONSHIP BETWEEN FORCES FIGURE The body sinks The body floats (is in equilibrium) anywhere in the liquid 2 Results of the experiment Behavior in the liquid Bodies, names of substances Plastic block (sinks or floats) 1000 1300 Wooden block ≈ 400 Piece of lead 11300 Piece aluminum 2700 Piece of polystyrene foam ≈ 20 Rubber cap ≈ 1200 Piece of plasticine ≈ 1400 Paraffin 900 Cork 240 Potato floats floats 3 Conditions for floating bodies BETWEEN RELATIONSHIPS BEHAVIOR OF BODIES DENSITIES BETWEEN FORCES FIGURE FT? FА ρBODY? ρLIQUID FTRAIN > FA FTRAIN< FА FТЯЖ = FА 4 Машинное масло Как располагаются тела в машинном масле? 5 Плотность какого тела больше? 3 1 2 ВЫВОД: чем меньше плотность тела по сравнению с плотностью жидкости, тем меньшая часть тела погружена в жидкость. 6 В сосудах плавают одинаковые тела. В каком из сосудов находится вода, морская вода, спирт? СПИРТ ВОДА МОРСКАЯ ВОДА ВЫВОД: чем больше плотность жидкости, тем меньшая часть тела погружена в жидкость. 7 Как расположатся несмешивающиеся жидкости в сосуде? Несмешивающиеся жидкости располагаются в сосуде в соответствии со своими плотностями. керосин вода Почему горящий керосин нельзя тушить водой? 8 Жидкости тоже могут плавать 9 МЕРТВОЕ МОРЕ Купаясь в этом море, человек очень мало погружается в воду, находясь как бы на поверхности, поскольку средняя плотность тела человека меньше плотности воды. В нашей стране еще более высокая плотность воды наблюдается в заливе Кара-Богаз-Гол на Каспии и в озере Эльтон. 10 НЕФТЯНЫЕ ПЯТНА Аварии на нефтеналивных танкерах, повреждения плавучих буровых наносят окружающей среде невосполнимый ущерб. Когда нефтяное пятно достигает берега, оно загрязняет пляжи, скалы, и это загрязнение почти невозможно устранить. Существуют специальные составы, которыми посыпают нефтяные пятна, чтобы они утонули. Но в этом случае они загрязняют дно и губят живущие там организмы. 11 ЛЕСОСПЛАВ вид транспортирования леса по воде, при котором используется плавучесть древесины. 12 АРЕОМЕТР - прибор для измерения плотности жидкости Ареометр представляет собой стеклянную трубку, нижняя часть которой заполнена дробью для удержания ареометра в вертикальном положении во время измерений. В верхней, узкой части находится шкала, которая проградуирована в значениях относительной плотности. 13 Можно ли заставить плавать тела, которые в обычных условиях тонут в воде? 14 ПЛАВАНИЕ РЫБ и млекопитающих Средняя плотность живых организмов, населяющих водную среду, близка к плотности окружающей их воды. Это и делает возможным их плавание под водой. Большую роль в передвижении рыб играет плавательный пузырь. Меняя объём пузыря, рыба способна как увеличивать, так и уменьшать действующую на неё выталкивающую силу. Киты регулируют глубину погружения за счет уменьшения и увеличения объема легких. 15 ПОДВОДНАЯ ЛОДКА Среднюю плотность подводной лодки можно подобрать так, чтобы она плавала внутри жидкости, всплывала или «тонула» – опускалось на дно. У подводной лодки есть балластные цистерны. Когда они наполняются морской водой, субмарина тяжелеет и погружается в воду. Когда резервуары опустошаются, субмарина становится легче, поднимается и держится на поверхности. 16 § 53,54. Плавание судов. Воздухоплавание. 17 «КАРТЕЗИАНСКИЙ ВОДОЛАЗ» 18 ЗАДАНИЯ № 1. Как располагаются жидкости (вода, ртуть, керосин) в сосуде? № 2. Как располагается деревянное тело (плотность которого равна 900 кг/м3), в воде, машинном масле, керосине и смеси воды с маслом? № 3. В сосуд, содержащий воду, керосин и жидкий растворитель (плотность которого равна 1595 кг/м3), опущены три шарика: парафиновый, пробковый и стеклянный. Как расположены шарики? Домашнее задание § 52, упр. 27 (5,6). Задание стр. 154,156. Спасибо за урок!!! так себе понравилось не понравилось 20
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