Physics 8 Lesson 10: Archimedes’ Thrust
1. Theoretical summary
1.1. The effect of a liquid on an object immersed in it.
An object immersed in a liquid is pushed vertically from the bottom by the liquid with a force equal to the weight of the liquid displaced by the object. This force is called the Archimedes repulsion force.
1.2. The magnitude of the Archimedes repulsion
a) Prediction
– Acsimet predicts:

The more the object is immersed in the liquid, the stronger the force of the water on the object.

The magnitude of the force exerted on an object immersed in the liquid is equal to the weight of the liquid displaced by the object.
b) Experiment
– B1: Measure P_{first} of cup A and the object.
– B2: Immerse the object in water → water overflows into the container. Measure weight P_{2}
– B3: Compare P_{2} and P_{first} : P_{2} < P_{first} => P_{first} = P_{2} + F_{A}
– B4: Pour spilled water from the container into cup A. Measure the weight
→ P_{first} = P_{2} + P_{overrun }

When an object is submerged in an overflow vessel, the volume of water that spills out is equal to the volume of the object. The object being pushed by water from below to the dynamometer reading is: \({P_2} = {\rm{ }}{P_1} – {\rm{ }}{F_A}\) .

When pouring water from B to A, the dynamometer shows P_{first}, proving that F_{A} is equal to the weight of the liquid displaced by the object
c) The formula for calculating the Archimedes thrust force
– Formula: \(F_{A}\) = d . DRAW
In which:

\(F_{A}\): Acsimeter thrust (N)

d: Specific gravity of the liquid (N/m^{2})

V: The volume of liquid displaced by the object (m^{3})
2. Illustrated exercise
Question 1: An aluminum ingot and a steel ingot of the same volume are immersed in water, which ingot experiences the greater Archimedes repulsion?
Solution guide
The two ingots are subjected to equal Arsium repulsion because the Arsium repulsion depends only on the specific gravity of the water and the volume of the water displaced by each ingot.
Verse 2: Please state the solution, then use the balance drawn in Figure 10.4 instead of the dynamometer to check the prediction of the magnitude of the Arsemometer thrust.
Solution guide
Step 1: Use a scale to weigh a small, waterproof weight that hangs under a beaker A placed on the weighing pan. The mass of the object and the cup (disc on the left) is exactly equal to the weight of the weights (disc on the right).
Step 2: The object is still hanging on the scale but is completely immersed in an overflow tank B filled with water, then some of the water in the overflow tank flows into cup C and the scale is deflected towards the weights.
Step 3: Still keeping the object in the overflow tank, and pouring water from cup C into cup A on the weighing pan, the balance will return to balance.
Thus, the Archimedes repulsion is equal to the weight of the displaced water.
3. Practice
3.1. Essay exercises
Question 1: Hanging an object in the air to the dynamometer, the dynamometer reads 2.1 N. Immersing the object in water reduces the reading of the dynamometer by 0.2 N. Ask how many times the substance makes the object have a specific gravity. times the specific gravity of water. Given that the specific gravity of water is 10000 N/m^{3}.
Verse 2: The volume of a piece of iron is 2dm^{3}. What is the repulsive force acting on the iron when immersed in water?
Question 3: An object has a specific gravity of 22000 N/m^{3}. Hanging the object on a dynamometer and then submerging the object in water, the dynamometer reads 30N. If the object is hung in the air, what is the dynamometer reading? Given that the specific gravity of water is 10000 N/m .^{3}.
Question 4: What forces are acting on an object in water?
3.2. Multiple choice exercises
Question 1: An aluminum ingot and a steel ingot of equal volume are submerged in water. Which the following comment is true?
A. The deeper the ingot, the greater the Archimedes force acting on that ingot.
B. Steel has a higher specific gravity than aluminum, so the steel ingot is subjected to a larger Arsiummeter thrust.
C. Both aluminum and steel ingots are subject to the same Archimedes repulsion because they are both immersed in the same water.
D. Both aluminum and steel ingots are subjected to the same Archimedes repulsion because they occupy the same volume in water.
Verse 2: Which of the following sentences is correct?
A. Archimedes thrust in the same direction as gravity.
B. The Archimedes force acts in all directions because the liquid exerts pressure in all directions.
C. Archimedes repulsion has a set point in the object.
D. Archimedes’ thrust is always equal to the weight of the object.
Question 3: The formula for calculating the Archimedes thrust is:
A. F_{A} = DV B. F_{A} = P_{object}
C. F_{A} = dV D. F_{A} = dh
Question 4: The Archimedes repulsive force acting on an object immersed in a liquid is equal to:
A. The weight of the object.
B. Weight of liquid.
C. Weight of the liquid displaced by the object.
D. The weight of the part of the object below the surface of the liquid.
4. Conclusion
Through this lesson, students will be familiar with the knowledge related to the azimuth Thrust along with related exercises at many levels from easy to difficult…, they need to understand:

State the characteristics of the Archimedes repulsion force.

Write the formula to calculate the magnitude of the repulsion Arsium meter, name the quantities, the units of those quantities.

Explain the simple and common phenomena involved.
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