## Physics 8 Lesson 11: Practice: Experimenting with Archimedes’ thrust

## 1. Theoretical summary

### 1.1. Experiment target

**– Knowledge:**

- Know: the formula for calculating the magnitude of the Archimedes repulsion, the units and quantities in the formula
- Understand: experimental plan on the basis of existing tools
- Using force measurement by dynamometer, measure liquid volume with graduated cylinder for experiment.

**– Skill: **Measure force, measure volume

**– Attitude: **Actively, carefully when doing experiments, cooperate when working in groups.

### 1.2. Laboratory instruments

For each group of students:

- A dynamometer 0 – 2.5N.
- An aluminum weight has a volume of about 50cm3.
- A graduated flask.
- A stand.

### 1.3. Experimental steps

**Step 1**: Measurement of thrust force Archimedes

- Measure the weight P of the object when it is placed in the air (H.11.1)
- Measure the force F acting on the dynamometer when the object is submerged in water (H.11.2)

**Step 2:** Measure the weight of the part of water whose volume is equal to the volume of the object.

- Measure the volume of a heavy object, which is also the volume of the liquid displaced by the object.

## 2. Practice report

**a) Answer the question:**

**C4** (page 42 Physics Textbook 8): Write the formula for calculating the Archimedes thrust. What are the names and units of the quantities present in the formula?

The answer:

The formula for calculating the Archimedes thrust force: F_{A} = dV

Where: d is the specific gravity of the liquid, unit: N/m3

V is the volume of liquid displaced by the object, unit: m3

**C5 **(page 42 Physics Textbook 8): What quantities need to be measured in order to verify the magnitude of the Archimedes thrust?

The answer:

To verify the magnitude of the Archimedes repulsion, we need to measure:

- The magnitude of the thrust force Archimedes (F
_{A}) - Weight of the liquid displaced by the object (P
_{WOMEN})

**b) Archimedes thrust measurement results:**

Average results:

**c. The result of measuring the weight of the part of water whose volume is equal to the volume of the object**

**d. Comment on measurement results and draw conclusions**

\(P = \frac{{{P_{{N_1}}} + {P_{{N_2}}} + {P_{{N_3}}}}}{3} = \frac{{0.7 + 0, 8 + 0.9}}{3} = 0.8\,N \)

Measurement results have errors, due to errors in the measurement process, or due to incorrect reading of the dynamometer value.

**Conclusion: **If the error in the measurement process is ignored, the Archimedes thrust has a magnitude equal to the weight of the liquid displaced by the object.

## 3. Practice

**Question 1:** The volume of a piece of iron is 2dm3. The repulsive force acting on the iron when immersed in water will receive which of the many values?

**Verse 2:** 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/m3.

**Question 3:** An object has a specific gravity of 22000 N/m3. 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/m3.

**Question 4:** An aluminum object and an alloy object have the same mass and are immersed in the same liquid. What is the greater force acting on the object that is repulsive? How many times bigger? Given that the specific gravity of aluminum and alloy is 27000 N/m3 and 67500 N/m3 respectively.

## 4. Conclusion

Through this Archimedes Repulsion Practice, you need to complete some of the goals that the lesson gives, such as:

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