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Background: Density may be defined as a measure of how much mass is contained in a given unit of volume (density = mass/volume) and is usually expressed in g/cm3.  In other words, if mass is a measure of how much “stuff” there is in an object, then density is a measure of how tightly that “stuff” is packed together.  In this lab, we will attempt to determine the density of the Earth.  As you already know, density is found by dividing the mass of an object by its volume.  Dr. Henry Cavendish is one of the first scientists that calculated the mass and density of the Earth.  He accomplished this by assembling a suspended metal rod with two lead balls hanging freely.  Cavendish then placed masses of metal near these balls in order to measure the force of attraction between them.  Based on this experiment, he was able to determine the attraction on a mass the size of the Earth and hence determine the Earth’s density.  This experiment has become known as the Cavendish Experiment.

Materials:

            triple beam balance

            graduated cylinder

            water

            calculator

            rock sample of basalt

            rock sample granite

            rock sample of slate

Procedure:

            1) Obtain tray of materials

            2) Using the triple beam balance, determine the mass of all rock samples

            3) Record these masses in the chart

            4) Using the method of water displacement, determine the volume of all rock samples

            5) Record the volumes in the chart

            6) Determine the densities of the rock samples

            7) Answer provided questions

Data Chart:

Questions:

 1. Determine the average density of the three (3) rock samples.  Record your result here __________.

 2. How does the density of the iron sample compare with the average density of the rock samples?

 3. Add the density of iron to the average density of the rock samples and divide by two (2.)  This value

     represents the density of the Earth.  Record your determined density here __________.

 4. Using the internet, find the known density of the Earth.  Record the density here __________.  How does your experimental

     value compare with the known density.

 5. What do you think might be the cause of any errors in this lab?

 6. What layer of the earth do the three (3) rock samples represent?

 7. What layer of the earth does the iron sample represent?

 8. Why is it not necessary to represent the mantle in this investigation?

Remember that when writing up your lab report, you must follow the proper format.

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