Archimedes’ principle and density
Weigh a metal block in air, in water and in salt solution to find the upthrust and the density of the metal.
Objectives
- Measure upthrust with a spring balance.
- Verify that upthrust equals the weight of liquid displaced.
- Find the density of a solid.
Theory
Archimedes’ principle: a body wholly or partly immersed in a fluid experiences an upthrust equal to the weight of fluid it displaces. So the balance reads less in a liquid: upthrust = weight in air − apparent weight. Fully immersed in water, the block displaces its own volume, so volume (cm³) = rise in water level (mL), and density = mass ÷ volume. A denser liquid gives a larger upthrust.
Upthrust = W(air) − W(liquid) Density = mass ÷ volume
Procedure
- Weigh block A in air.
- Lower the block fully into water and read the balance and the water level.
- Repeat in salt solution.
Precautions
- The block must be fully immersed and must not touch the cylinder.
- Read the balance at eye level.
- Subject
- Physics
- Grade
- 8–10
- Chapter
- Pressure (Nepal National Curriculum (CDC), grade 9)
- Difficulty
- Easy
- Duration
- 20 min
- Safety level
- Low
- Version
- 1.0
Apparatus
- Spring balance (0–5 N)
- Measuring cylinder
- Water
- Salt solution
- Metal blocks
- Thread
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