'Solar Stew' Investigating Planet Densities Lab



Lab: Investigating Planet Densities

Introduction:

The Big Bang theory is one of the most widely accepted theories explaining the formation of the universe. According to this theory, all matter and energy in the universe was once concentrated in an extremely small volume. When the so-called "big bang" occurred about 17 billion years ago, matter and energy were propelled outward in all directions as the universe began to expand. In time, the expanding matter began to condense and collect in smaller clouds of dust and gas to form galaxies. The cloud of dust and gas that gradually condensed to form our solar system is called the solar nebula. This hypothesis that our entire solar system condensed out of the same spinning cloud of gas and dust is known as the nebular theory.

At the center of the solar nebula, a star, the sun, began to form as the mass continued to contract. While the sun was forming, the leftover material, a "solar stew" called planetesimals, orbited the sun and gradually coalesced (combined) to form the planets. The denser materials remained closer to the sun, while the lighter gases formed bodies further away.

Density is defined as the ratio of the mass of a substance to its volume, and is measured in g/cm3 for solids. But what does that really mean? A steel sphere will feel heavier than an aluminum sphere of the same size. In this example, the volume of both spheres is the same; however, the steel sphere contains more mass. Density depends on the kind of atoms a substance contains and also how tightly the atoms are packed together. Steel, for example, contains iron, which has an atomic mass that is more than twice that of aluminum. It is a heavier element, so the density of steel will be greater than that of aluminum for a given volume.

Density for a regularly shaped object, like a cube, block, or cylinder, can be found by obtaining the mass of the object using a balance, and by measuring the dimensions of the object to determine the volume. Once the mass (m) and volume (V) are determined, the density (D) can be calculated as follows:

Density = mass measured in g/cm3 (solids) or g/ml (liquids) volume

Water displacement is another method of obtaining the volume of both regularly and irregularly shaped objects in order to calculate density. Determining the volume of an object by this method is relatively simple. A graduated cylinder is filled with water to a given volume. The test object is placed in the cylinder, and the volume of water displayed increases by the amount of space occupied by the object. For example, a cylinder is filled with 50 ml of water. An object inserted into the cylinder raises the water level to 81 ml. The difference between water levels is 31 ml so the volume of the object is 31 cm3. This method of determining volume will be used in this laboratory investigation.

Purpose: In this activity, you will calculate the densities of sample test materials in the "solar stew" and try to determine, by density, which planet the materials represent.

Materials

1 Graduated Cylinder. 100ml

1 Beaker, 250ml

1 Set of 9 Density Samples

1 Metric Balance

1 Pipet

1 Calculator

Water

Procedure

1. Locate the 9 density samples provided for this activity. Using a metric balance, determine the mass for each "ingredient" of the "solar stew" to the nearest 0.1 g.

2. Record the mass for each sample in the appropriate column in DATA TABLE 1.

3. Using the water displacement method, obtain the volume of each "ingredient". First, fill a beaker about 2/3 full with water. Use the beaker to pour about 70 ml of water into the graduated cylinder. With a pipet, add or remove any water from the cylinder to adjust the level to exactly 70 ml.

4. Next, carefully slip the "ingredient" test sample into the cylinder, being careful not to splash any of the water. You may want to tilt the cylinder slightly so that the sample slides slowly into the cylinder without splashing.

5. Note the new volume level for the water in the cylinder, and estimate to the nearest 0.1 ml. The volume of the sample is the difference between the new volume and the original volume.

6. Repeat this process for all 9 samples. (Note: Several of your test samples will actually float on the water. To determine their volumes, you will need to use a pencil or other object to push and hold the sample down just below the water level in the cylinder, then read the new level.)

7. Record the volume of each sample "ingredient" in the appropriate column in data table.

8. Calculate the density of the samples by dividing the mass of the substance by its volume. (Remember: a volume of 1 ml is equivalent to 1 cm3)

9. Record your calculated densities to the nearest 0.1 g/cm3 in the appropriate column in the data table

10. Determine which substance comes closest to matching the density for each planet by comparing their values with those found in DATA TABLE 2.

11. Record the matching "stew ingredient" in the appropriate column in the table.

Questions

1. What happens to the overall density of the planets as one travels outward from the sun?

2. Why do you think this is so?

3. Which two substances were NOT used for the planetary densities?

4. Which was the heavier of the two substances NOT used? Where is this substance found in the solar system? Explain your answer in terms of the nebular theory.

5. Use the nebular theory to state what happens to the lighter materials in the solar system, as represented by the less dense of the two substances referred to in Question #3.

6. The mass of Jupiter is 1.9 x 1030g. The mass for Earth is 5.98 x 1027g. Use this data and the information from DATA TABLE 2 to calculate the volume for Jupiter and Earth. Show all work; don't forget the units.

7. Using your data from Question #6, how many Earths would fit into Jupiter?

8. Using the mass data from Question #6, how many Earths would it take to equal the mass of Jupiter?

9. With a density of 1.3 g/cm3 for Jupiter, calculate what its volume WOULD be if it had the mass of Earth. How many times the size of Earth would this planet be?

Observations and Data

Data Table 1

|SUBSTANCE |MASS (g) |VOLUME (ml') |DENSITY (g/cm3) |

|acrylic | | | |

|chalcocite | | | |

|clay | | | |

|cork | | | |

|iron | | | |

|magnetite | | | |

|pinewood | | | |

|rubber | | | |

|sphalerite | | | |

|PLANET |DENSITY (g/cm3) |"STEW" |ACTUAL PLANET |

| | |INGREDIENT |COMPOSITION |

|Mercury |5.4 | |Silicates, iron |

|Venus |5.2 | |Silicates, iron |

|Earth |5.5 | |Silicates, iron |

|Mars |3.9 | |Silicates, iron |

|Jupiter |1.3 | |Hydrogen, helium |

|Saturn |0.7 | |Hydrogen, helium |

|Uranus |1.3 | |Hydrogen, helium, |

| | | |methane |

|Neptune |1.8 | |Hydrogen, helium, |

| | | |methane |

|Pluto |1.1 (?) | |Methane, rock, ice (?) |

Data Table 2

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