# Relative Density Laboratory Report

Topics: Density, Buoyancy, Soft drink Pages: 8 (2402 words) Published: December 7, 2011
Experiment 6: Relative Density
Laboratory Report

Jessica Manansala, Nathaniel Martinez,
Maria Pacia, Jeanelle Pedrigal, Miguel Poblete

Department of Math and Physics
College of Science, University of Santo Tomas
España, Manila Philippines

Abstract
The experiment would introduce us to 3 concepts, namely, the definition of relative density, the Archimedes principle and the determination of density by the Archimedes principle. In the first activity, we were tasked with finding the density of a cylinder of a known metal; this was done by submersing the cylinder of metal in a measured amount of water and calculating the displaced water against the measured mass of the cylinder. The next activity required us to compute for the density of a given bone. The bone was first weighed, submersed in water and then weighed again. After which the relative density was then computed. The third activity required us to measure the weights of diet and regular soft drinks and then compute for their density.

Introduction
Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity usually means relative density with respect to water. The term "relative density" is often preferred in modern scientific usage.

If a substance's relative density is less than one then it is less dense than the reference; if greater than 1 then it is denser than the reference. If the relative density is exactly 1 then the densities are equal; that is, equal volumes of the two substances have the same mass. If the reference material is water then a substance with a relative density (or specific gravity) less than 1 will float in water. For example, an ice cube, with a relative density of about 0.91, will float. A substance with a relative density greater than 1 will sink. [1] Archimedes' principle relates buoyancy to displacement. It is named after its discoverer, Archimedes of Syracuse. Archimedes' treatise, On floating bodies, proposition 5 states: Any floating object displaces its own weight of fluid.

— Archimedes of Syracuse
For more general objects, floating and sunken, and in gases as well as liquids (i.e. a fluid), Archimedes' principle may be stated thus in terms of forces: Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object. — Archimedes of Syracuse

With the clarifications that for a sunken object the volume of displaced fluid is the volume of the object, and for a floating object on a liquid, the weight of the displaced liquid is the weight of the object. More tersely: buoyancy = weight of displaced fluid. [2]

The objectives of this experiment are to determine the composition of a substance based on its density, to determine the density of a liquid by using a pycnometer, and to determine the density of a substance by Archimedes principle.

Theory

1. Density - is defined as its mass per unit volume.
D= mV
Eq. 1

Density of bone=R.D.x density of water
Eq. 2

2. Relative Density – is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material.

3. Relative density of bone is weight of the bone in air over weight in air minus the weight of the bone in water. R.D.= wAwA- wW
Eq. 3

4. Relative density of Reg. Coke is weight of reg. coke minus the weight of the pycnometer over the weight of water minus weight of pcynometer. R.D.of Reg.Coke=wR-wPwW-wP
Eq. 4

5. Relative density of Diet Coke is weight of diet coke minus the weight of the pycnometer over the weight of water minus the weight of the pycometer. R.D.of Diet Coke= wD- wPwW- wP
Eq. 5

Methodology

Activity 1:
A piece of brass was first weighed using an electronic gram balance. Water was then placed a graduated cylinder to a level of 60 ml. The weighed cylinder was then placed in the water and the...