FyT: Laboratorio Nº3 - Principio de Arquímedes

Summary

The laboratory demonstrates Archimedes’ principle by measuring three cylindrical objects—aluminum, brass, and iron—in air and while submerged in water. Its goals are to calculate the buoyant force and determine each object’s density.

Equipment and materials

• Three-arm balance, tripod, and support rod
• Graduated cylinder and water container
• String
• Cylindrical samples of aluminum, brass, and iron

Procedure

1. Set up and zero the balance. Place the balance on its support, set all three counterweights to zero, and adjust the pointer until it also reads zero.
2. Measure each object’s mass in air. Suspend the object from the balance and record its mass in kilograms in Table 2.
3. Calculate its actual weight. Multiply the mass by gravitational acceleration, using (g = 9.8) or (9.81\ \text{m/s}^2). Record the result in Table 3.
4. Measure the apparent weight in water. Suspend the object in the graduated cylinder without letting it touch the walls or bottom. Add water until the level reaches the top of the object, then record the balance reading and convert it to apparent weight using (W = mg).
5. Determine the displaced volume. Record the water volume with the object submerged, then remove the object and record the resulting water level. The difference between the readings is the object’s volume. Convert milliliters to cubic meters.
6. Calculate density and compare results. Divide mass by volume to obtain experimental density. Compare it with the reference density provided in the laboratory guide and calculate the percentage error.
7. Repeat the measurements and calculations for aluminum, brass, and iron, then complete the tables and answer the guide’s questions.

The buoyant force is the reduction in the object’s measured weight when submerged:

[ F_B = \text{actual weight} - \text{apparent weight} ]

Brass example and conclusions

For brass, the presenter reports:

• Mass: 106.8 g
• Actual weight: 1.04664 N
• Apparent weight: 0.92022 N
• Water volume with the object submerged: 180 mL
• Water volume after the object is removed: 168 mL
• Displaced volume: 12 mL
• Reference density: 8600 kg/m³
• Reported density error: about 3.49%

Another error value, 3.73175, is also mentioned, but its specific association is unclear.

The presenter says the errors shown in the tables fall within a stated acceptable range of approximately ±3.1% to ±4.1%. They emphasize that careful measurements are important because poor data can substantially increase the error.

Transcript correction: The subtitles give an incorrect cubic-meter conversion for 12 mL. The correct conversion is (12\ \text{mL} = 12 \times 10^{-6}\ \text{m}^3 = 0.000012\ \text{m}^3). This is consistent with the reported brass density and error.

Speakers and sources featured

• Unnamed instructor/presenter: Introduces the lab, explains the equipment and procedure, and demonstrates measurements.
• Explanatory narration or voice-over, speaker unidentified: Describes the brass example, calculations, and results; it may be the same presenter.
• Referenced materials: The laboratory guide (for reference densities and instructions) and an Excel spreadsheet (for organizing measurements and calculating results).