about Archimedes’ principle and learn to use it using English vocabulary.
Introduction
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We already know that the hydrostatic pressure depends on the height of the liquid column, the density of the liquid and the standard gravity.
We measure body density as a ratio of body mass to its volume.
We measure the weightweightweight of a body using a dynamometer or a suitable weight.
Experiment 1
Experiment 1
Research problem
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Does water affect the weightweightweight of the body immersed in it.
Hypothesis
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The real weight of the body does not change, but the apparent weight of the body immersed in water is smaller than the weight of the same body in the air.
You will need
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a) dynamometer, b) tripod, c) cuboids of the same dimensions, made of various metals, e.g. copper, aluminium and iron, d) beaker with water.
Instruction
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1. Using the dynamometer, determine the weightweightweight of this cuboid. 2. Record the result in the table. 3. Immerse the suspended cuboid completely in a beaker of water; do not immerse the hook of the dynamometer itself. 4. Read the result again and record the dynamometer readings. 5. Make the same measurements for the other cuboids.
Save the results of the experiment in the table.
Copper cuboid
Iron cuboid
Aluminium cuboid
Body weight, dynamometer readings in the air F [N]
Dynamometer readings when the body is immersed in FIndeks dolny waterwater [N]
Difference between the above readings FIndeks dolny ww = F - FIndeks dolny waterwater
Summary
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Experiment has shown that the dynamometer reading during the measurement when the body was immersed in water is smaller than during the measurement when it was in the air.
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Conclusions
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The difference between measurements does not depend on the material from which the rectangles are made, and is always constant, provided that their volumes are the same.
The observed regularity applies to all liquids.
An additional force acts on the body immersed in any liquid, which has the opposite direction with respect to the force of gravityforce of gravityforce of gravity.
This force is called the buoyancy force, and its value does not depend on the type of substance from which the immersed body is made.
Task 1
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Give the names of the forces shown in the figure.
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Perform the experiment according to the given scheme.
Experiment 2
Experiment 2
Research problem
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What determines the buoyant force?
Summary
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The buoyant forcebuoyant forcebuoyant force depends on the type of liquid in which the body is completely immersed.
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The buoyant force depends on the volume of the immersed body.
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Perform the experiment according to the given scheme.
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Perform the experiment under the supervision of an adult.
Experiment 3
Experiment 3
Research problem
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What does the buoyant force depend on?
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Hypothesis
The buoyant force does not depend on the body shape, liquid volume, immersion depth, body weightweightweight.
You will need
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a) beakers of various volumes, b) water, c) dynamometer. d) plasticine ball, e) cord.
Instruction
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1. Hang the ball on a cord. 2. Determine the weightweightweight of the ball with a dynamometer. 3. Immerse the ball completely in beakers of various volumes of water. 4. Read the dynamometer readings. 5. Immerse the ball in water - read the dynamometer readings. 6. Change the shape of the ball and repeat step 5. 7. Immerse the ball in a measuring cylinder filled with water and read the value of the buoyant force at the different depth of the ball's immersion.
Summary
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The buoyant force does not depend on the shape of the body (point 6 of the instructions).
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The buoyant forcebuoyant forcebuoyant force does not depend on the volume of liquid in which it is immersed (point 3 of the instructions).
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The buoyant force does not depend on the immersion depth of the body (point 7 of the instructions).
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Conclusions
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The buoyant force acting on the body immersed in the liquid depends on the density of the liquid and the volume of the immersed body. The buoyant force does not depend on the shape of the body, body weightweightweight, liquid volume, immersion depth.
Based on the above‑mentioned experiments, we can formulate the content of Archimedes' principle.
For every body immersed in a liquid there is a buoyant force which is directed upward and equal in magnitude to the weight of the displaced liquiddisplaced liquiddisplaced liquid.
The magnitude of buoyant force FIndeks dolny ww is calculated according to the formula:
where: d - density of displaced liquid, V - volume of displaced liquid, g - standard gravity.
Exercise 1
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Answer the question.
Is Archimedes' principle valid for bodies immersed in gas?
Suggest a way to confirm the validity of the principle for gases.
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a) Archimedes' right is also valid for bodies immersed in gas because the volume of gas displaced by the body also has its own weight.
b) Archimedes' principle for gases can be checked with a balloon filled with hydrogen or helium.
Summary
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The buoyant forcebuoyant forcebuoyant force affects the body immersed in liquid or gas.
The buoyant force is always directed upward.
The buoyant force depends on the density of the liquid or gas and the volume of the body immersed in the liquid or gas.
Archimedes' principle: For each body immersed in a liquid (or gas), there is a buoyant force that is directed upward and equal in magnitude to the weightweightweight of the displaced liquiddisplaced liquiddisplaced liquid (or displaced gas).
The buoyant force can be calculated using the formula:
where: d - density of displaced liquid, V - volume of displaced liquid, g - standard gravity.
Exercises
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Exercise 2
Exercise 3
A figurine of volume of 50 cmIndeks górny 33 and a weight of 250 g was immersed in water. What is the net force acting on this figurine? What is the magnitude of the buoyant force? (the density of water is d = 1 ).
The net force is 2 N and the buoyant force is 0,5 N.
Exercise 4
Write in English what value the dynamometer would indicate after immersing a bag filled with water in water and why?
According to Archimedes' principle, we can state that the buoyant force is equal to the weight of the liquid displaced by the body immersed in the liquid. Because the water bag immersed in water has the same density as water in which the water bag is immersed, the weight of the water bag will be balanced by the buoyant force equal to the weight of the volume of displaced water. Because the buoyant force acting on the bag is equal to the weight of the bag, the apparent weight of the bag indicated by the dynamometer is zero newton (0 N). The buoyant force balanced the weight of the bag with water.