A spring whose composition is not completely known might be...

A spring whose composition is not completely known might be either bronze (sp gr 8.8) or brass (sp gr 8.4). It has a mass of $1.26 \mathrm{~g}$ when measured in air and $1.11 \mathrm{~g}$ in water. Which is it made of?

Key Concepts

Density Measurement Using Weight Difference in Fluids

By measuring the weight of an object in air and then in water, one can use the difference (which equals the weight of the displaced water by Archimedes Principle) to calculate the object's volume. Dividing the object's mass by its volume yields its density, which can then be compared to known densities of candidate materials like bronze and brass.

Specific Gravity

Specific gravity is a dimensionless quantity that represents the ratio of the density of a material to the density of water. It helps in characterizing materials such as bronze and brass, allowing for a comparison of their densities to identify which material the object is likely made of.

Archimedes Principle

This principle states that a body completely or partially submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces. It is essential for determining the effective weight loss when the object is immersed in water, and thus allows us to calculate the volume of the object based on the displaced fluid volume.

Buoyancy

Buoyancy is the upward force exerted by a fluid on an object immersed in it. In this context, it explains why the object's apparent weight in water is less than its weight in air, and the difference between these measurements is directly related to the volume of the object.

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