Dr. Dinosawer answers all your questions on physics

Just what it sounds like.

Re: Dr. Dinosawer answers all your questions on physics

Postby Lum » Sun Aug 21, 2016 1:24 pm

In The Expanse books, Gauss cannons are mounted on ships ;) I believe they never mention coilguns. I'm only starting Book #3 so... :ghost:
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Re: Dr. Dinosawer answers all your questions on physics

Postby IronDuke » Mon Aug 22, 2016 11:06 am

Thanks, Dino. That makes perfect sense. You're considerably better at explaining than Wikipedia is with their insane mathematical equations. :monkey:
Also, I read 5 (I think?) books of The Expanse, and I don't recall anything but railguns in there. :think:

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Re: Dr. Dinosawer answers all your questions on physics

Postby 0111narwhalz » Mon Aug 22, 2016 11:39 am

IronDuke wrote:Also, I read 5 (I think?) books of The Expanse, and I don't recall anything but railguns in there. :think:

Pretty sure the railguns are long-range ship-ship guns and the Gauss cannons were PDC's.
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Re: Dr. Dinosawer answers all your questions on physics

Postby IronDuke » Mon Aug 22, 2016 11:41 am

Ah, I never figured out what the PDCs were exactly. I assumed they were electromagnetic, but wasn't sure.

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Re: Dr. Dinosawer answers all your questions on physics

Postby Lum » Mon Aug 22, 2016 12:15 pm

0111narwhalz wrote:
IronDuke wrote:Also, I read 5 (I think?) books of The Expanse, and I don't recall anything but railguns in there. :think:

Pretty sure the railguns are long-range ship-ship guns and the Gauss cannons were PDC's.


Exactly. They call point defens cannons (PDCs) Gauss cannons sometimes. And railguns are for insane ship to ship hole-doing from far away.
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Re: Dr. Dinosawer answers all your questions on physics

Postby DWMagus » Wed Aug 24, 2016 1:47 pm

Alright, let's have some fun.

Why does carbon fiber have such a bad shear strength vs it's tensile strength?
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Re: Dr. Dinosawer answers all your questions on physics

Postby Cornflakes_91 » Wed Aug 24, 2016 1:52 pm

I'd guess because its "glued" together fibers with high tensile strength.

The fibers themself dont give much support in directions that arent pulling on any of them, they just flex. And place all of the stress on the "supplemental" epoxy
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Re: Dr. Dinosawer answers all your questions on physics

Postby Grumblesaur » Fri Aug 26, 2016 5:10 pm

Do you guys actually draw free body diagrams or do you use computer software? :ghost:
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Re: Dr. Dinosawer answers all your questions on physics

Postby IronDuke » Wed May 17, 2017 12:36 pm

If you apply a force off of the center of mass of an object, how much angular acceleration does it provide? What's the formula/equation/thingy for this?

E.G. For maneuvering thrusters, I need to know how much force to apply at the thruster location to get a specific angular acceleration. My physics book seems to cover everything except that. :monkey:

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Re: Dr. Dinosawer answers all your questions on physics

Postby Cornflakes_91 » Wed May 17, 2017 12:43 pm

angular acceleration = force * lever lenght (distance from CoM) / moment of inertia

dont forget that that also still applies a linear acceleration as usual if you have unbalanced thrust

edit:

example tables of moments of inertia for a couple of objects
https://en.wikipedia.org/wiki/List_of_m ... of_inertia
Last edited by Cornflakes_91 on Wed May 17, 2017 12:52 pm, edited 1 time in total.
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Re: Dr. Dinosawer answers all your questions on physics

Postby Scytale » Wed May 17, 2017 12:46 pm

Cornflakes_91 wrote:angular acceleration = force * lever lenght (distance from CoM) / moment of inertia

dont forget that that also still applies a linear acceleration as usual if you have unbalanced thrust


And crucially the moment of inertia must be calculated in the plane that the torque is applied
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Re: Dr. Dinosawer answers all your questions on physics

Postby Cornflakes_91 » Wed May 17, 2017 12:48 pm

yeah, thats important :ghost:
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Re: Dr. Dinosawer answers all your questions on physics

Postby IronDuke » Wed May 17, 2017 1:07 pm

Oooh, thanks guys! This is super simple :oops: helpful! :thumbup: :D

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Re: Dr. Dinosawer answers all your questions on physics

Postby Cornflakes_91 » Wed May 17, 2017 1:10 pm

IronDuke wrote:Oooh, thanks guys! This is super simple :oops: helpful! :thumbup: :D

--IronDuke


you can take variations of the "3D inertia tensors" from my link and adapt them to spaceships (for example the ellipsoid one adapted to the dimensions of the ship)
and just put your x,y,z torques into those formulas (attention with signs!)
to get a probably passable approximation.
with "only" 7 variables attached to the ship

and to avoid having to calculate accurate moments of inertia for your ships :ghost:
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Re: Dr. Dinosawer answers all your questions on physics

Postby Scytale » Wed May 17, 2017 1:10 pm

IronDuke wrote:Oooh, thanks guys! This is super simple :oops: helpful! :thumbup: :D

--IronDuke


Uh dude if you're implementing 3D dynamics that stuff is super complicated

The equations of motion get really busy
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