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I want to calculate the gravitational force between the Earth and its Moon using Newton's gravitational formula: (G M1 M2)/d^2 and its appropriate physical units. I'd include the code I wrote for this question, but I don't know how to display it. Thank you for help.

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    $\begingroup$ You can format inline code and code blocks by selecting the code and clicking the {} button above the edit window. The edit window help button ? is useful for learning how to format your questions and answers. You may also find this meta Q&A helpful $\endgroup$ – Michael E2 Oct 1 '17 at 23:49
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FormulaLookup["force of gravity"]

(* {"NewtonsLawOfUniversalGravitation"} *)

FormulaData["NewtonsLawOfUniversalGravitation"]

enter image description here

g = Quantity[1, "GravitationalConstant"]; 
m1 = Quantity[1, "EarthMass"]; 
m2 = PlanetaryMoonData["Moon", "Mass"]; 
r = PlanetaryMoonData["Moon", "DistanceFromEarth"]; 

{g, m1, m2, r}

enter image description here

{g, m1, m2, r} // UnitConvert

(* {Quantity[6.674*10^-11, ("Meters")^3/("Kilograms" ("Seconds")^2)], 
 Quantity[5.9721986*10^24, "Kilograms"], 
 Quantity[7.3459*10^22, "Kilograms"], Quantity[3.90946*10^8, "Meters"]} *)

f = g*m1*m2/r^2 // UnitConvert

(* Quantity[1.91575*10^20, ("Kilograms" "Meters")/("Seconds")^2] *)

EDIT: Note that PlanetaryMoonData["Moon", "DistanceFromEarth"] is not a constant but is dynamically updated to reflect the varying value due to the Moon's orbit not being circular.

PlanetaryMoonData["Moon", "DistanceFromEarth"] // UnitConvert

(* Quantity[3.88389*10^8, "Meters"] *)

Depending on your needs, you can use the average value

PlanetaryMoonData["Moon", "AverageDistanceFromEarth"] // UnitConvert

(* Quantity[3.850*10^8, "Meters"] *)
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    $\begingroup$ Could also be done directly with: FormulaData["NewtonsLawOfUniversalGravitation", { "r" -> PlanetaryMoonData["Moon", "DistanceFromEarth"], Subscript["m", 1] -> Quantity[1, "EarthMass"], Subscript["m", 2] -> PlanetaryMoonData["Moon", "Mass"] } ] $\endgroup$ – chuy Oct 2 '17 at 14:32

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