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freefall acceleration (simple physics)

Started by Crispy Oct 17, 2004 at 5:12 PM 12 replies 700+ views
Original Post
Crispy
Crispy
I'm a little bogged. UGC (universal gravitational constant) G = 6.67x10-11 = 0.0000000000667 N m2/kg2 Earth's mass me = 5.98x1015 kg Earth's radius re = ~6373 km Freefall acceleration gm = G*me/re2 = ~0 What am I doing wrong? PS - I don't even have math or physics at school, so this isn't a homework thing. On a related note, I can't seem to find the ASCII code for the "cross" I could use instead of the asterisk "*" to denote multiplication. It seems it's not part of the ANSI standard. My keyboard has it on the numpad, but Windows only prints an asterisk.
"Literally, it means that Bob is everything you can think of, but not dead; i.e., Bob is a purple-spotted, yellow-striped bumblebee/dragon/pterodactyl hybrid with a voracious addiction to Twix candy bars, but not dead."- kSquared
Hedos
Hedos
Quote:
Original post by Crispy
On a related note, I can't seem to find the ASCII code for the "cross" I could use instead of the asterisk "*" to denote multiplication. It seems it's not part of the ANSI standard. My keyboard has it on the numpad, but Windows only prints an asterisk.


Here it is: x
Crispy
Crispy
Quote:
Original post by Hedos
Quote:
Original post by Crispy
On a related note, I can't seem to find the ASCII code for the "cross" I could use instead of the asterisk "*" to denote multiplication. It seems it's not part of the ANSI standard. My keyboard has it on the numpad, but Windows only prints an asterisk.


Here it is: x


No, silly - not the ex: the cross that's vertically centered on the line. I occasionally type it by accident, but now that I need it, I can't find it - it doesn't even appear to be in the Character Map. I'm sure it's there, even though I've looked like a bazillion times now...
"Literally, it means that Bob is everything you can think of, but not dead; i.e., Bob is a purple-spotted, yellow-striped bumblebee/dragon/pterodactyl hybrid with a voracious addiction to Twix candy bars, but not dead."- kSquared
Hedos
Hedos
this: ┼ ?

ALT+453

And I would call this the addition symbol, not multiplication.
Crispy
Crispy
Nope. It's shaped like the ex (as opposed to the plus), but not as high and centered verically (which I already said...).
"Literally, it means that Bob is everything you can think of, but not dead; i.e., Bob is a purple-spotted, yellow-striped bumblebee/dragon/pterodactyl hybrid with a voracious addiction to Twix candy bars, but not dead."- kSquared
Xtremehobo
Xtremehobo
Here ya go: ×

Hooray for google [grin]
pixelwrench.com | [email="matt[nospam]@pixelwrench[nospam]com"]email[/email] lethalhamster: gamedev keeps taking my money, but im too lazy to not let them
Salsa
Salsa
*scratches head*

It didn't appear in my character map either. You know, I bet if you never asked, it would still be there, too.
Kult House - Fresh Production Media
smart_idiot
smart_idiot
× = ×
Chess is played by three people. Two people play the game; the third provides moral support for the pawns. The object of the game is to kill your opponent by flinging captured pieces at his head. Since the only piece that can be killed is a pawn, the two armies agree to meet in a pawn-infested area (or even a pawn shop) and kill as many pawns as possible in the crossfire. If the game goes on for an hour, one player may legally attempt to gouge out the other
thebolt00
thebolt00
Hi

What you have got a bit wrong is the mass of Earth, it is not 5.98x1015 kg, but rather 5.98x1024 kg. Substitute with the correct mass in your calculation, and you get gm = 9.8206

-M
Hedos
Hedos
×
No idea how to type it though, sorry
trzy
trzy
Quote:
Original post by Crispy
I'm a little bogged.

UGC (universal gravitational constant) G = 6.67x10-11 = 0.0000000000667 N m2/kg2

Earth's mass me = 5.98x1015 kg

Earth's radius re = ~6373 km

Freefall acceleration gm = G*me/re2 = ~0

What am I doing wrong?


Using your data, I calculated the acceleration to be 9.82E-9 m/s^2. It looked like an error of magnitude, because otherwise the numbers are correct, so I double-checked your data and you've got the mass of the Earth wrong by a factor of 10^9:

Mass of Earth: 5.97E24 kg
Radius (mean): 6.38E3 km = 6.38E6 m

Do the math now and you should get 9.7991 m/s^2.
----Bart
smart_idiot
smart_idiot
Teh noes! Somebody has ran off with 99.9999999% of my favorite planet!
Chess is played by three people. Two people play the game; the third provides moral support for the pawns. The object of the game is to kill your opponent by flinging captured pieces at his head. Since the only piece that can be killed is a pawn, the two armies agree to meet in a pawn-infested area (or even a pawn shop) and kill as many pawns as possible in the crossfire. If the game goes on for an hour, one player may legally attempt to gouge out the other
nagromo
nagromo
Quote:
Original post by Crispy
I'm a little bogged.

UGC (universal gravitational constant) G = 6.67x10-11 = 0.0000000000667 N m2/kg2

Earth's mass me = 5.98x1015 kg

Earth's radius re = ~6373 km

Freefall acceleration gm = G*me/re2 = ~0

What am I doing wrong?



PS - I don't even have math or physics at school, so this isn't a homework thing.

On a related note, I can't seem to find the ASCII code for the "cross" I could use instead of the asterisk "*" to denote multiplication. It seems it's not part of the ANSI standard. My keyboard has it on the numpad, but Windows only prints an asterisk.


Your equation gives 9.8*10-9; are you sure your measurements are correct (including units)? Google gave M = 5.98*1024 kg, which gives g = 9.8 m/s2

[edit]: Wow I'm slow!
Crispy
Crispy
Yay! Thanks, extreemhobo!

Hedos: you can copy-paste it from the browser :). And since it's not Unicode, it compiles just fine.

thebolt: you're absolutely right - I'm calculating the mass from scratch and getting 15. Have to recheck everything... Thanks.

Edit: hold on - I'm probably going to copy-paste some more stuff in a moment...



Aight - I went over it and I think I have my prequisite data right (so the error is still somewhere in the calculations).


1) ρ = 5.52 g/cm3 (density)
2) req = 6378.5 km (radius on equator)
3) rp = 6356.9 km (radius at poles)
4) v = 4 × π × req2 × rp / 3.f = 1.08×1015 km3
5) me = ρ × v = 5.98×1015 kg

It's the same from here on.

PS: Was GD just down? Didn't get to finish point 5...

Oh - I see it now - I'm not converting cm3 to km3.

[Edited by - Crispy on October 17, 2004 6:32:32 PM]
"Literally, it means that Bob is everything you can think of, but not dead; i.e., Bob is a purple-spotted, yellow-striped bumblebee/dragon/pterodactyl hybrid with a voracious addiction to Twix candy bars, but not dead."- kSquared

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