Is there a calculator for earth rotation?

Allium · Sep 28, 2019

Boy this opened a long closed door. Found myself skimming FM 6-40 Filed Artillery manual. We used to have to keep all that in mind when firing - drift, bore condition, rotation, temp of powder, temp and wind speed at altitudes. All books and slide rules. No calculators - Ok we had one but took 4 to comfortably carry so it frequently got dropped. Get info, fill in chart, get standard adjustment. Ages ago.

GuitarmanNick · Sep 29, 2019

I used to do these calculations in my head when making the throw from third to first as a kid.

Docster · Sep 29, 2019

gtodave said:
I guess I'll have to figure out how many pounds a 140 grain bullet weighs. Thanks!

That depends on how far your bullet is from the center of the earth and how close the earth is to the sun at the time you weigh the bullet :lol2:

DivingDriver · Sep 29, 2019

Compared to that my first post sucked.

trickg · Oct 1, 2019

GuitarmanNick said:
I used to do these calculations in my head when making the throw from third to first as a kid.

I like that. :party29:

GotoDave, I'm curious - did you win or lose the bet?

Sirex · Oct 1, 2019

See, if you just believe in Flat Earth, you won't have to worry about this.

gtodave · Oct 1, 2019

trickg said:
I like that.

GotoDave, I'm curious - did you win or lose the bet?

Winning. I was working on a formula to calculate this last Friday, but have been too busy to complete it. I'm hoping one pops up here in the meantime :innocent0

gtodave · Oct 1, 2019

Sirex said:
See, if you just believe in Flat Earth, you won't have to worry about this.

Alan3413 · Oct 2, 2019

If we had a phased plasma rifle, none of this would matter.

aray · Oct 2, 2019

Ok we need a new MDS award: the IslandCrLeverGun Award for the most awesome first post of the year.

This year’s award is already claimed.

Downside: the expectation bar for the second post is set pretty darned high.

onedash · Oct 2, 2019

pretty sure it's 3%.

trickg · Oct 2, 2019

gtodave said:
Winning. I was working on a formula to calculate this last Friday, but have been too busy to complete it. I'm hoping one pops up here in the meantime

That's easy enough to find - this is the formula:

Fc=2×V×A×sinel

where Fc = Coriolis effect, V = wind velocity, A = angular velocity of the earth, and l = latitude.

Maybe a little easier to read this way:

Fc = 2*V*A*sinel

Interestingly, the formula doesn't account for direction of North, South, East or West.

This is a fun one though - to calculate A, the angular velocity of the Earth, you need to consider this:

"Mathematically, the average angular velocity of an object can be represented by the following equation: ωaverage= Δθ/Δt, where ω is the radians/revolutions per second (on average), Δ is the change in quantity, θ is the velocity, and t is time. When calculating the angular velocity of the Earth as it completes a full rotation on its own axis (a solar day), this equation is represented as: ωavg = 2πrad/1day (86400 seconds), which works out to a moderate angular velocity of 7.2921159 × 10-5 radians/second. In the case of a Solar Year, where ωavg = 2πrad/1year (3.2×107 seconds), we see that the angular velocity works out to 2.0×10-7 rad/s."

This all makes my head hurt.

Alan3413 · Oct 2, 2019

I'm getting flashbacks of college algebra and wanting to curl up in fetal position.

Oldline6 · Oct 2, 2019

Hall of Fame Material!

on_the_rox said:
Ok, that has to rank pretty high up in the realm of first posts......

Just saying.

Fair point!

trickg · Oct 2, 2019

Alan3413 said:
I'm getting flashbacks of college algebra and wanting to curl up in fetal position.

Oh it's far worse than algebra - this is calculus!

Oldline6 · Oct 2, 2019

trickg said:
Oh it's far worse than algebra - this is calculus!

In Sanskrit...

Eddie Van · Oct 2, 2019

gtodave said:
Is there a calculator online that will tell me how much the target "moves" with the Earth's rotation at given distances and time? I'm trying to figure out how much a 6.5CM is affected by planet rotation at 1,000 yards. I know it isn't much, but I was looking for precise numbers.

EDIT: just saw TRICKG answered this last week and that awesome first post, I should've read the full thread before spouting off! oh well....

My calcs using the posted omni calculator and these assumptions:

140 gr bullet (0.02 lbf)
time to target at 1000yds (t): 1.2 sec
formula for effect (distance,x) of Coriolis acceleration (a) on bullet is x = 1/2*a*t^2 (a is acceleration from Omni calc)

a = .236 ft/sec^2 for a 140gr bullet at 37 deg of latitude

distance is 0.5*1.2^2*.236 = .1699 feet or about 2 inches

That would be maximum effect (i.e. shooting due North or South). If target is due East or West of shooter, Coriolis acceleration would be greatly diminished

ralph.mclean · Oct 2, 2019

It can be calculated based upon longitude, latitude, facing direction, and height above sea-level.

If you find the right calculator, you can also plug in humidity and barometric pressure.

Too much math for me.

Bob A · Oct 2, 2019

Do these figures take into account the decrease in bullet velocity over time?

Dovk0802 · Oct 2, 2019

Allium said:
Boy this opened a long closed door. Found myself skimming FM 6-40 Filed Artillery manual. We used to have to keep all that in mind when firing - drift, bore condition, rotation, temp of powder, temp and wind speed at altitudes. All books and slide rules. No calculators - Ok we had one but took 4 to comfortably carry so it frequently got dropped. Get info, fill in chart, get standard adjustment. Ages ago.

I was wondering how to convince Aberdeen that they needed to publish a TFT for 6.5...
and
Don't forget to add two forks...

Is there a calculator for earth rotation?

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