Notes

The amount of material (mass) in a given space (or volume) is called density. Each material has a unique density.
We will use the units grams per cubic centimeter (g/cm3) to report density.
NOTEBOOK has density
Great job! Metal is our densest planet building substance. It has the most number of molecules in a given volume. Gas is the least dense and has the least amount of molecules in a given volume. Given that, if you have the same volumes, then metal will have the most molecules (mass) in that volume, while gas will have the least
NOTEBOOK
Good work. Recall that an extrinsic property is something that can be varied freely and doesn't depend on the substance. Mass and volume are extrinsic properties because you can change them easily. An intrinsic property is one that is inherent to a substance or system. It cannot be changed easily because it is a built-in feature. Density is an intrinsic property because is depends on the type of substance, not on how much of it there is.

mass = 0.64 x 10^27 g

radius = 3400 km


Convert radius to centimeters

3400 km x 100,000 cm/km = 3.4 x 108 cm

density = (0.64 x 10^27 g) / (4/3 x x (3.40 x 10^8 cm)^3)
in SCI CALCULATOR(0.64×10^27)÷(4÷3×pi×(3.40×10^8)^3)

density = 3.89 g/cm3
VOLUME SCI CAL=(4/3*3.14*(10^8)^3) USE http://www.calculatorsoup.com/calculators/physics/density.php CAL V GIVEN P to check this answer.
That's correct! We previously looked at the microscropic view of these substances. Now we have some numbers to attach to those views. The densities of planetary materials range from 0.5 g/cm3 (gas) to 8 g/cm3 for metal.
Now let's go use these materials to build some planets!

WHEN ASKED TO AND THREE WATER
Great work. Because volume is an extrinsic property, it is additive. If we stick three Earth-sized planets together, they will take up the same amount of space together as when they are apart.
Density, on the other hand, is an intrinsic property. The density of water is 1 g/cm3. It doesn't matter how much water you have, the density of water is 1 g/cm3. If it isn't, it's not water.
E.I add volume keep density
WHEN ADDING ONE WATER AND ONE METAL
WATER=V=1 D=1
METAL=V=1 D=8
ANSWER= V=2 D=7
Good job! Even when mixing different substances together, extrinsic properties like volume are additive.
But what happens to density? Because we now have a water-metal mixture, the density of the entire object must lie between the densities of each individual substance. For this particular combination, the density of the combined object would be 4.5 g/cm3, halfway between that of water (1 g/cm3) and metal (8 g/cm3).
But it really depends on the volumes you are mixing. If you had more water (low density), then the overall density would be lower. If you had more metal (high density), the overall density would be higher.
NOTE BOOK
Remember that transit photometry reveals the size of a planet, hence its radius. Radial velocity reveals the mass of a planet.

Now that we know how to calculate density, how density maps to materials, and how densities mix when materials mix, we can begin to reconstruct planets.

12
Planet Modeling


We have a problem, though ... we have one density and four materials to reconstruct this density. That means the possibility of multiple (degenerate) solutions. What should we do?
gas + metal + water =4.5 g/cm^3

gas + rock =4.5 g/cm^3

water + metal + gas = 4.5 g/cm^3
When multiple solutions are possible, it is best practice to select the simplest, or most parsimonious, solution.


This principle is also known as Occam's razor ... the simplest solution is usually (but not always) the correct one
This planet has a density of 7.2 g/cm3. What is the minimum number of materials that can account for this density?

ANSWER =2
Good job. The density does not exactly match any of our singular materials. However, it would match if we mixed two of them. We could mix more, but the simplest solution is two different materials.
HOW THESE ARE EXPRESSED WHEN QUESTIONS APPEAR
CONVERTION FACTORS
1 ME = 5.97 x 10^27 grams (MASS)****

1 RE = 6.37 x 10^8 cm (RADIUS)****
USE THESE ^

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