• Log InLog In
  • Register
Liquid`
Team Liquid Liquipedia
EDT 10:28
CEST 16:28
KST 23:28
  • Home
  • Forum
  • Calendar
  • Streams
  • Liquipedia
  • Features
  • Store
  • EPT
  • TL+
  • StarCraft 2
  • Brood War
  • Smash
  • Heroes
  • Counter-Strike
  • Overwatch
  • Liquibet
  • Fantasy StarCraft
  • TLPD
  • StarCraft 2
  • Brood War
  • Blogs
Forum Sidebar
Events/Features
News
Featured News
[ASL20] Ro8 Preview Pt2: Holding On9Maestros of the Game: Live Finals Preview (RO4)5TL.net Map Contest #21 - Finalists4Team TLMC #5: Vote to Decide Ladder Maps!0[ASL20] Ro8 Preview Pt1: Mile High15
Community News
Weekly Cups (Sept 29-Oct 5): MaxPax triples up2PartinG joins SteamerZone, returns to SC2 competition245.0.15 Balance Patch Notes (Live version)107$2,500 WardiTV TL Map Contest Tournament 151Stellar Fest: StarCraft II returns to Canada11
StarCraft 2
General
5.0.15 Balance Patch Notes (Live version) WoL: how does "advanced construction" work? Weekly Cups (Sept 29-Oct 5): MaxPax triples up PartinG joins SteamerZone, returns to SC2 competition ZvT - Army Composition - Slow Lings + Fast Banes
Tourneys
RSL Offline Finals Dates + Ticket Sales! Tenacious Turtle Tussle Stellar Fest $2,500 WardiTV TL Map Contest Tournament 15 Sparkling Tuna Cup - Weekly Open Tournament
Strategy
Custom Maps
External Content
Mutation # 494 Unstable Environment Mutation # 493 Quick Killers Mutation # 492 Get Out More Mutation # 491 Night Drive
Brood War
General
RepMastered™: replay sharing and analyzer site BW General Discussion Question regarding recent ASL Bisu vs Larva game BGH Auto Balance -> http://bghmmr.eu/ [ASL20] Ro8 Preview Pt2: Holding On
Tourneys
[Megathread] Daily Proleagues [ASL20] Ro8 Day 4 [ASL20] Ro8 Day 3 Small VOD Thread 2.0
Strategy
Proposed Glossary of Strategic Uncertainty Current Meta TvZ Theorycraft - Improving on State of the Art 9 hatch vs 10 hatch vs 12 hatch
Other Games
General Games
Stormgate/Frost Giant Megathread ZeroSpace Megathread Nintendo Switch Thread Dawn of War IV Path of Exile
Dota 2
Official 'what is Dota anymore' discussion LiquidDota to reintegrate into TL.net
League of Legends
Heroes of the Storm
Simple Questions, Simple Answers Heroes of the Storm 2.0
Hearthstone
Deck construction bug Heroes of StarCraft mini-set
TL Mafia
SPIRED by.ASL Mafia {211640} TL Mafia Community Thread
Community
General
Things Aren’t Peaceful in Palestine UK Politics Mega-thread Russo-Ukrainian War Thread US Politics Mega-thread The Games Industry And ATVI
Fan Clubs
The herO Fan Club! The Happy Fan Club!
Media & Entertainment
Anime Discussion Thread Movie Discussion! [Manga] One Piece
Sports
2024 - 2026 Football Thread Formula 1 Discussion MLB/Baseball 2023 NBA General Discussion TeamLiquid Health and Fitness Initiative For 2023
World Cup 2022
Tech Support
SC2 Client Relocalization [Change SC2 Language] Linksys AE2500 USB WIFI keeps disconnecting Computer Build, Upgrade & Buying Resource Thread
TL Community
Recent Gifted Posts The Automated Ban List BarCraft in Tokyo Japan for ASL Season5 Final
Blogs
[AI] From Comfort Women to …
Peanutsc
Mental Health In Esports: Wo…
TrAiDoS
Try to reverse getting fired …
Garnet
[ASL20] Players bad at pi…
pullarius1
Customize Sidebar...

Website Feedback

Closed Threads



Active: 1464 users

A Physics or Math Question

Blogs > LegendaryDreams
Post a Reply
LegendaryDreams
Profile Blog Joined November 2004
Canada1350 Posts
January 29 2008 00:49 GMT
#1
The nearest decent-sized celestial body to the earth is the moon. But we don`t orbit about that. To see why we orbit about the sun, rather than orbit about the moon, work out how much stronger the force of gravity is from the sun than the force of gravity from the moon. All you need to know is that the sun is about 30 million (3x10 to the 7) times as massive as the moon, and about 400 times further away.

call me moxie
fanatacist
Profile Blog Joined August 2007
10319 Posts
Last Edited: 2008-01-29 00:53:16
January 29 2008 00:51 GMT
#2
Use gmM/r^2.

g = gravitation constant
m = mass 1
M = mass 2
r = distance from centers of mass

(Google the gravitation constant, I think it is something like 6.637 x 10^-11 but I haven't used it in a while so I may be mistaken)\

EDIT: Actually, you don't need the constant, since it's just a ratio. If you want me to do it for you, respond I guess.
Peace~
LegendaryDreams
Profile Blog Joined November 2004
Canada1350 Posts
January 29 2008 01:06 GMT
#3
Um it would be nice to see how anyone does this question. Because I don't have much physics background I'm not sure whether to use just plain math or find some physics formulas for it.
call me moxie
BottleAbuser
Profile Blog Joined December 2007
Korea (South)1888 Posts
Last Edited: 2008-01-29 01:11:56
January 29 2008 01:07 GMT
#4
Er, yeah. I'm bored, so everyone reading this will have to see my mess.

I'm going to arbitrarily call the mass of Earth x, the mass of the moon y, and the mass of the sun y*3*10^7. The distance between Earth and moon is 1 in arbitrary units, and distance between Earth and sun is 400. (All givens.)

Now, given equation G = g * mM*r^-2

z * G(moon) = G(sun), and we're solving for z.

Plugging in values for g, m, M, and r for each side of the equation:

xyzg = xyg *3*10^7 * 400^-2

Simplifying:

z = 3 * 10 ^ 7 * 160000 ^ -1
= 3 * 10 ^ 2 / 1.6
which is roughly z = 200

So, the pull on Earth by the sun is about 200 times stronger than the pull on Earth by the moon. Unless I've dropped a zero somewhere or a sign. Which would be embarrassing as hell.

Compilers are like boyfriends, you miss a period and they go crazy on you.
BottleAbuser
Profile Blog Joined December 2007
Korea (South)1888 Posts
January 29 2008 01:10 GMT
#5
Also, if we are to orbit around closest body, we should take a look at any two objects in the air that are closer to each other than the ground. They are closer to each other, why don't they orbit around each other instead of being dominated by the pull of Earth? Easy to see why "closer, but why don't they orbit each other instead of some further x"
Compilers are like boyfriends, you miss a period and they go crazy on you.
eVo[LvE]
Profile Joined December 2007
Canada19 Posts
January 29 2008 01:16 GMT
#6
You don't happen to take AST201 this semester at University of Toronto, do you? XDDD
ID: evo[lve]
BottleAbuser
Profile Blog Joined December 2007
Korea (South)1888 Posts
Last Edited: 2008-01-29 01:19:36
January 29 2008 01:18 GMT
#7
o.o CS at a Korean school.

Maybe you ask OP because you've seen same problem as hw?
Compilers are like boyfriends, you miss a period and they go crazy on you.
fanatacist
Profile Blog Joined August 2007
10319 Posts
Last Edited: 2008-01-29 01:32:20
January 29 2008 01:26 GMT
#8
On January 29 2008 10:07 BottleAbuser wrote:
Er, yeah. I'm bored, so everyone reading this will have to see my mess.

I'm going to arbitrarily call the mass of Earth x, the mass of the moon y, and the mass of the sun y*3*10^7. The distance between Earth and moon is 1 in arbitrary units, and distance between Earth and sun is 400. (All givens.)

Now, given equation G = g * mM*r^-2

z * G(moon) = G(sun), and we're solving for z.

Plugging in values for g, m, M, and r for each side of the equation:

xyzg = xyg *3*10^7 * 400^-2

Simplifying:

z = 3 * 10 ^ 7 * 160000 ^ -1
= 3 * 10 ^ 2 / 1.6
which is roughly z = 200

So, the pull on Earth by the sun is about 200 times stronger than the pull on Earth by the moon. Unless I've dropped a zero somewhere or a sign. Which would be embarrassing as hell.


Uh... I think that's wrong. Here is the solution I made, maybe you can find a mistake:

Well, GmM/R^2 is an old formula for gravitation and orbitting of planets. It measures the strength of gravitation between two objects, so it is perfect in this context.

Here is how I would solve it:

m1 = Sun
m2 = Moon
M = Earth
R1 = Distance from Sun to Earth
R2 = Distance from Moon to Earth

Gm1M/R1^2 = Strength of gravitation of Sun to Earth

Gm2M/R2^2 = Strength of gravitation of Moon to Earth

So, to answer your question, we simply plug in the data we know.

Sun = 30 million times more massive than the Moon, so

m1 = 3 * 10^7 * m2

Sun = 400 times further away than the Moon, so

R1 = 4 * 10^2 * R2

So, now we simply plug in the data back into the original formula, and compare them as a ratio

Strength of Gravitation
Sun : Moon
Gm1M/R1^2 : Gm2M/R2^2
G(3 * 10^7 * m2)M/(4 * 10^2 * R2)^2 : Gm2M/R2^2

Here we can already see that you can divide both sides by G and M. This leaves us with:

(3 * 10^7 * m2)/(4 * 10^2 * R2)^2 : m2/R2^2

Now we can divide both sides by m2 and multiply by R2^2, to have a pure number ratio:

(3 * 10^7)/(4 * 10^2)^2 : 1/1
(3 * 10^7)/(16 * 10^4) : 1
(3/16)(10^3) : 1
187.5 : 1

Obviously, the Sun's force of gravity on the Earth is much greater than the Moon's. In fact, it is 187.5 times stronger! I hope you understood my broken English, I can try to clarify parts n_n.


Although, like you said, you might have fucked up. I think my work is neater and in more steps.

EDIT: HAHA forgot to square R. Hold on.

EDIT 2: Fixed. I fucking suck. My defense is that I did this 3 years ago T_T.
Peace~
BottleAbuser
Profile Blog Joined December 2007
Korea (South)1888 Posts
January 29 2008 01:39 GMT
#9
Yay for nitpicking.

The givens are to 1 significant digit (distance ratio is closer to 390, mass ratio is closer to 2.7*10^7). Answer should also be to 1 significant digit.
Compilers are like boyfriends, you miss a period and they go crazy on you.
fanatacist
Profile Blog Joined August 2007
10319 Posts
January 29 2008 01:43 GMT
#10
On January 29 2008 10:39 BottleAbuser wrote:
Yay for nitpicking.

The givens are to 1 significant digit (distance ratio is closer to 390, mass ratio is closer to 2.7*10^7). Answer should also be to 1 significant digit.

This level of physics is barely an accurate measure worthy of significant figures, I believe, because GmM/R^2 basically assumes that the planets are spherical point-masses, so it doesn't hurt to ignore sig figs in this, just like you would in a math problem. At least that's the way I was taught this relatively low-difficulty conceptual physics stuff. It's not like read-outs from chemistry conversions and experiments xD.
Peace~
BottleAbuser
Profile Blog Joined December 2007
Korea (South)1888 Posts
Last Edited: 2008-01-29 01:56:47
January 29 2008 01:56 GMT
#11
Nitpick wars begin!

It's valid to treat them as spheres (and spheres are equivalent to point masses in this model), because they're very damn similar to perfect spheres, and the composition is very uniform among any given shell within those spheres.

It's always a good thing to observe significant figures! In pure mathematics, there is no uncertainty (even with probability your level of uncertainty is very certain), so there is no need for significant figures. When we're talking about models of the real world (be it chemical reactions or bigger objects), we're using measurements as input, and those always have some level of uncertainty... and significant figures is how we deal with the uncertainty!
Compilers are like boyfriends, you miss a period and they go crazy on you.
LxRogue
Profile Blog Joined March 2007
United States1415 Posts
Last Edited: 2008-01-29 02:25:24
January 29 2008 02:23 GMT
#12
On January 29 2008 09:49 LegendaryDreams wrote:
The nearest decent-sized celestial body to the earth is the moon. But we don`t orbit about that. To see why we orbit about the sun, rather than orbit about the moon, work out how much stronger the force of gravity is from the sun than the force of gravity from the moon. All you need to know is that the sun is about 30 million (3x10 to the 7) times as massive as the moon, and about 400 times further away.


You don't need any constants or stuff, you just compare the two forces with the inverse square law.

Gm1m2/r^2 = Gm1m2/r^2

G and m1 (mass of the earth) cancel out and you know the relationship between the distances and m2.

30,000,000 * m2 / (400r)^2 = m2 / r^2

so the force due to the sun is 30,000,000 / 400^2 times as strong or 187.5 times as strong as the moons force.

(edit: whoops i guess im the 3rd person to get this)
fanatacist
Profile Blog Joined August 2007
10319 Posts
January 29 2008 02:59 GMT
#13
On January 29 2008 10:56 BottleAbuser wrote:
Nitpick wars begin!

It's valid to treat them as spheres (and spheres are equivalent to point masses in this model), because they're very damn similar to perfect spheres, and the composition is very uniform among any given shell within those spheres.

It's always a good thing to observe significant figures! In pure mathematics, there is no uncertainty (even with probability your level of uncertainty is very certain), so there is no need for significant figures. When we're talking about models of the real world (be it chemical reactions or bigger objects), we're using measurements as input, and those always have some level of uncertainty... and significant figures is how we deal with the uncertainty!

Close... But not quite it. I think it's inferred that the answer 187.5 isn't meant to be taken as an accurate value - it's the mathematical result to a mathematical problem. It's obviously not exact, just like GmM/R^2 may be close but not exact either. If we wish to be technical, then yes in this case, as a physics problem, we would use sig figs. But as a math problem, (title = Math/Physics problem), that is the exact answer. You can implement sig figs at the end depending on what the problem is looking for, so isn't it better to give the exact mathematical answer and then let the OP decide which is more appropriate?

Also, the OP's issue was more conceptual than mathematical, so either way I would not have cared about finer details such as sig figs, which I personally feel are unnecessary outside of finalized lab reports or final solutions to problems. This was just the methodology to solving the problem, and the exact mathematical result. I treated it as a math problem, ratios and all, independent of the real-world correlation. Didn't see much of a point in being so detailed about it .
Peace~
Luddite
Profile Blog Joined April 2007
United States2315 Posts
January 29 2008 05:42 GMT
#14
To be fair, the earth does orbit around the center of the earth-moon system. A little bit.
Can't believe I'm still here playing this same game
eVo[LvE]
Profile Joined December 2007
Canada19 Posts
January 29 2008 06:56 GMT
#15
On January 29 2008 10:18 BottleAbuser wrote:
o.o CS at a Korean school.

Maybe you ask OP because you've seen same problem as hw?


Yeah I meant the OP lol.

Thats the exact question on an assignment due this week :D
ID: evo[lve]
BottleAbuser
Profile Blog Joined December 2007
Korea (South)1888 Posts
Last Edited: 2008-01-29 08:12:18
January 29 2008 08:11 GMT
#16
That's a cue for "It's a Small World" theme song. C'mon, start playing it!
Compilers are like boyfriends, you miss a period and they go crazy on you.
fanatacist
Profile Blog Joined August 2007
10319 Posts
January 29 2008 15:49 GMT
#17
On January 29 2008 14:42 Luddite wrote:
To be fair, the earth does orbit around the center of the earth-moon system. A little bit.

And every mass has a force on every other object in the universe xD. It's not nearly strong enough in comparison to the sun's gravitational force. The Earth wobbles a little bit, at most.
Peace~
Please log in or register to reply.
Live Events Refresh
Map Test Tournament
11:00
TLMC #15: Group A
WardiTV1009
ComeBackTV 538
IndyStarCraft 218
Rex139
3DClanTV 92
EnkiAlexander 42
LiquipediaDiscussion
[ Submit Event ]
Live Streams
Refresh
StarCraft 2
IndyStarCraft 218
Rex 139
LamboSC2 126
ProTech78
StarCraft: Brood War
Britney 37904
Bisu 5791
Shuttle 3965
Sea 2124
Larva 1657
Mini 1354
hero 893
Light 882
GuemChi 781
Snow 694
[ Show more ]
Soulkey 591
firebathero 538
Soma 367
Rush 338
sorry 226
Zeus 112
Mind 90
Sea.KH 81
Backho 79
ToSsGirL 66
Free 59
Aegong 56
sas.Sziky 47
ivOry 43
JulyZerg 21
ajuk12(nOOB) 14
scan(afreeca) 10
NaDa 10
Hm[arnc] 9
Terrorterran 4
Dota 2
Gorgc6000
qojqva3112
Cr1tdota1191
Dendi1026
BananaSlamJamma223
PGG 110
Counter-Strike
fl0m1891
oskar102
olofmeister101
Other Games
singsing3023
hiko850
B2W.Neo776
crisheroes460
DeMusliM369
Lowko276
Pyrionflax261
Sick161
Hui .151
Mew2King56
Organizations
Other Games
BasetradeTV47
StarCraft 2
Blizzard YouTube
StarCraft: Brood War
BSLTrovo
sctven
[ Show 18 non-featured ]
StarCraft 2
• poizon28 7
• intothetv
• Kozan
• sooper7s
• AfreecaTV YouTube
• Migwel
• LaughNgamezSOOP
• IndyKCrew
StarCraft: Brood War
• Azhi_Dahaki17
• STPLYoutube
• ZZZeroYoutube
• BSLYoutube
Dota 2
• C_a_k_e 3283
• WagamamaTV422
League of Legends
• Nemesis3773
• Jankos1491
• TFBlade513
Other Games
• Shiphtur43
Upcoming Events
PiGosaur Monday
9h 32m
Map Test Tournament
20h 32m
OSC
1d 1h
MaNa vs Harstem
ByuN vs TBD
HiGhDrA vs NightPhoenix
Iba vs Ziomek
TriGGeR vs MindelVK
Lemon vs TBD
YoungYakov vs PAPI
ArT vs sebesdes
Tenacious Turtle Tussle
1d 8h
The PondCast
1d 19h
Map Test Tournament
1d 20h
OSC
2 days
Map Test Tournament
2 days
OSC
2 days
Korean StarCraft League
3 days
[ Show More ]
CranKy Ducklings
3 days
Map Test Tournament
3 days
OSC
4 days
[BSL 2025] Weekly
4 days
Safe House 2
4 days
Sparkling Tuna Cup
4 days
Map Test Tournament
4 days
OSC
4 days
IPSL
5 days
dxtr13 vs Napoleon
Doodle vs OldBoy
Liquipedia Results

Completed

BSL 20 Team Wars
Maestros of the Game
HCC Europe

Ongoing

BSL 21 Points
ASL Season 20
CSL 2025 AUTUMN (S18)
Acropolis #4 - TS2
C-Race Season 1
IPSL Winter 2025-26
WardiTV TLMC #15
EC S1
ESL Pro League S22
Frag Blocktober 2025
Urban Riga Open #1
FERJEE Rush 2025
Birch Cup 2025
DraculaN #2
LanDaLan #3
StarSeries Fall 2025
FISSURE Playground #2
BLAST Open Fall 2025
BLAST Open Fall Qual
Esports World Cup 2025
BLAST Bounty Fall 2025
BLAST Bounty Fall Qual
IEM Cologne 2025

Upcoming

SC4ALL: Brood War
BSL Season 21
BSL 21 Team A
RSL Revival: Season 3
Stellar Fest
SC4ALL: StarCraft II
eXTREMESLAND 2025
ESL Impact League Season 8
SL Budapest Major 2025
BLAST Rivals Fall 2025
IEM Chengdu 2025
PGL Masters Bucharest 2025
Thunderpick World Champ.
CS Asia Championships 2025
TLPD

1. ByuN
2. TY
3. Dark
4. Solar
5. Stats
6. Nerchio
7. sOs
8. soO
9. INnoVation
10. Elazer
1. Rain
2. Flash
3. EffOrt
4. Last
5. Bisu
6. Soulkey
7. Mini
8. Sharp
Sidebar Settings...

Advertising | Privacy Policy | Terms Of Use | Contact Us

Original banner artwork: Jim Warren
The contents of this webpage are copyright © 2025 TLnet. All Rights Reserved.