Physics with Falcon (and others)

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7/30/2021 8:56 AM

OK guys, I've been thinking of starting a physics thread, because I love the subject and I'm somewhat knowledgeable in the basics. However, even though I've had a few college courses, I'm no expert. Therefore, I'd love it if you guys who know more than I do can help out in this thread. Please post up!

My first entry will be to criticize a movie I saw once: Speed 2. Their first mistake was not to get Keanu back for the sequel; the second was to make that steaming pile of drivel in the first place.

The third is a gigantic error in their understanding of physics. In the movie, a cruise ship is hijacked, and the bridge is locked with the steering pointing at a port of call. The engines are all-ahead full, and the massive ship plows into the beach, then continues up the surface of the land for quite some time. All this is plausible, and in fact something with that much mass would, in fact, continue moving for a long time.
Where the mistake is made was obviously for effect, but it actually makes me angry: the main character is standing in some anteroom when the impact with the beach occurs. The director used all kinds of multiple-angle shots of the guy flailing through the air, crashing through windows, rolling across the deck, crashing through more windows and doors, then finally coming to rest after grabbing onto a handrail at the very front of the ship. Apparently, they wanted to illustrate how much mass and power are brought to bear when a ship runs aground.
There are two problems here: One, the standing man's inertia would only carry him with whatever velocity he carried in his mass alone when the ship stops; not some massive, unstoppable force. Two, since the ship is so massive and takes a long time to slow down, the difference between all-ahead full and all-ahead full with the hull scraping on the ground would be small. In fact, a man standing on the deck of such a ship would feel a jolt but might not even lose his balance.
The movie misunderstands there is a big difference between inertia, a body's tendency to remain in motion, and velocity, which is speed in a specific direction.

Let's hear some more movie mistakes, cool tidbits, unique experiences, and other physics fun facts. cool

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Braaapin' aint easy.

7/30/2021 10:36 AM
Edited Date/Time: 7/30/2021 10:39 AM

The "bank effect" causing the ever green ship to get stuck in suez was interestingly devastating.

edit: is hydrodynamics apart of physics?

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7/30/2021 10:45 AM

I’m in Romania atm, and everything seems a little off physically🤷🏻‍♂️
Weed and hores next door😬
Photo

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7/30/2021 10:57 AM


I thought this was cool... but then again, im an idiot.

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7/30/2021 11:38 AM

Falcon wrote:

OK guys, I've been thinking of starting a physics thread, because I love the subject and I'm somewhat knowledgeable in the ...more

As you correctly pointed out, the standing man would only have a certain amount of intertia. The even more interesting part is that since the ship doesn't stop instantly, the man's inertia must be expressed over time as either acceleration relative to the ship, or as a constant, and compared against the rate of deceleration of the ship

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7/30/2021 8:50 PM

Sunhouse wrote:

I’m in Romania atm, and everything seems a little off physically
Weed and hores next door
Photo

The brass and red stanchions really give that place a classy feel.

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7/31/2021 6:57 AM

Sunhouse wrote:

I’m in Romania atm, and everything seems a little off physically
Weed and hores next door
Photo

SEE ARE125 wrote:

The brass and red stanchions really give that place a classy feel.

and the red carpet. That place is for VIPs

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7/31/2021 8:14 AM
Edited Date/Time: 7/31/2021 8:15 AM

Had an awesome science teacher my freshman year of high school Mr Williams... looked like Johnathan Winters EXACTLY! He was so great he pulled even the slowest learners up a grade or two.
Sophomore year he has a student teacher come in for biology/chem1 and that moron could only read out of a tect book. Was horrible ... didn't matter as we moved a month into the school year.
Teachers can make a difference.

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7/31/2021 9:10 AM

On YouTube look up julius sumner miller. Videos are about 15 min each. They are old videos, but he shows a lot of cool things.

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7/31/2021 9:18 AM

How about in almost every movie car crash when one car rear ends another one and is somehow magically launched 30’ into the airlaughing

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7/31/2021 11:30 AM

sumdood wrote:

How about in almost every movie car crash when one car rear ends another one and is somehow magically launched 30’ into the ...more

Yeah, there was one Fast and Furious where a tanker truck just rolled and bounced and rolled and bounced for like 30 seconds all the way down the highway. I used to do heavy duty towing, and 9/10 times they just lay over on their side. The only exception was if it went off a cliff, then it may do a full rollover. Not to mention 80,000lbs doesn’t bounce. lol It was almost as painful as seeing someone riding an XR400 in the movies while hearing the sound effects of a 125. laughing

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7/31/2021 7:33 PM

I like you Falcon. I have a really hard time getting into movies for reasons like this because my mind works the same way.

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7/31/2021 9:12 PM

So, do you weigh more at the poles than at the equator?

Theory being that at the equator you have centrifugal force acting against the earth’s gravity, but the same can’t be said for at the poles…

And if you did weigh more at the poles, how would you know? The bathroom scales would be affected by the same amount…

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8/1/2021 4:34 AM

Sunhouse wrote:

I’m in Romania atm, and everything seems a little off physically
Weed and hores next door
Photo

The usual trip report required please Sir 😬

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8/1/2021 1:33 PM

Falcon wrote:

OK guys, I've been thinking of starting a physics thread, because I love the subject and I'm somewhat knowledgeable in the ...more

There's a Video from during The Zombie Apocalypse where they're driving Modern Cruise Ships UP ON TO THE BEACH...& it's awesome...

Oh, and it makes your point.

I'm jus' sayin'...

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Nobody ever told me, I found out for myself. You've got to believe in foolish miracles. It's not how you play the game, it's if you win or lose. You can choose. Don't confuse. Win or lose. It's up to you!

8/1/2021 6:17 PM

Robgvx wrote:

So, do you weigh more at the poles than at the equator?

Theory being that at the equator you have centrifugal force acting ...more

You most certainly do weigh more at the poles. I read the amount once and it was significant. I can't remember how much, but it was nearly a pound for an average person, I think.

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Braaapin' aint easy.

8/1/2021 11:56 PM

Sunhouse wrote:

I’m in Romania atm, and everything seems a little off physically
Weed and hores next door
Photo

Get blazed, pull yourself into a backflip and relax with a bottle of Jacks and Cigars.
In that order. Romaniacs indeed.

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8/2/2021 10:43 AM

Robgvx wrote:

So, do you weigh more at the poles than at the equator?

Theory being that at the equator you have centrifugal force acting ...more

Falcon wrote:

You most certainly do weigh more at the poles. I read the amount once and it was significant. I can't remember how much, but ...more

Here's a great read about it. Pretty concise, as well: https://www.wtamu.edu/~cbaird/sq/2014/01/07/do-i-weigh-less-on-the-equator-than-at-the-north-pole/#:~:text=Yes%2C%20you%20weigh%20less%20on,as%20you%20approach%20the%20poles.

I didn't think to mention before that the slight bulge at the equator lessens your body weight also, since you are slightly farther away from the center of the Earth.

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Braaapin' aint easy.

8/2/2021 11:13 PM
Edited Date/Time: 8/3/2021 3:21 AM

Robgvx wrote:

So, do you weigh more at the poles than at the equator?

Theory being that at the equator you have centrifugal force acting ...more

Falcon wrote:

You most certainly do weigh more at the poles. I read the amount once and it was significant. I can't remember how much, but ...more

Falcon wrote:

Here's a great read about it. Pretty concise, as well: ...more

Another one I like is the idea that if you could travel to the centre of the earth you would be weightless, as gravity would be pulling up in all directions at once, not just down.

And if there was a hole straight through the earth and you jumped down it, you would cycle back and forth (you’d be going ‘up’ once you passed the centre and so would reverse direction).

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8/3/2021 9:13 AM

Here's one that my friend, who is a rifleman, just won't believe:

A bullet, upon leaving the muzzle of a gun, drops to the ground as quickly as if you had dropped it from your hand.

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Braaapin' aint easy.

8/3/2021 11:13 AM

Falcon wrote:

Here's one that my friend, who is a rifleman, just won't believe:

A bullet, upon leaving the muzzle of a gun, drops to the ...more

Only if the barrel was level right? If I shoot it up it wont be coming down for a while. If I shot it straight down off a cliff it would hit ground sooner.

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8/3/2021 11:26 AM

Another fun topic (although not exactly physics) is a scoped rifle sighted in at say 1000 yards will appear to have the point of impact hit higher and higher as it leaves the barrel untill it crosses the line of sight then fall again untill crosses line of sight again and it hits its target. Often times this can result in a shot at say 100 yds hitting low, then it will zero farther out then hit high farther than that then rezero again at your 1000yd zero. Its easier to draw than explain with words, but pretty cool to whitness. Its especially noticable with air rifles at closer ranges.

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8/3/2021 11:28 AM

Yes, a dead level rifle.
The bullet starts dropping immediately.

I've had this argument so many times.
People think that since many larger caliber rounds can be zero at 25 and 100 yards but high at 50, the bullet "must" be going up at 25, and somewhere around 50 starts back down .

It's just "line of sight". Bullets can't do that.

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Go for it! Don't let a little thing like fear, or common sense hold you back.

8/3/2021 11:53 AM

Dang, got me thinking of more gun related physics.

Typically a heavier bullet for a given caliber will require more twist to stabilize it, not necessarily because of the weight but because of the length. See you cant make the bullet and bigger around so the heavier ones are longer to gain the extra weight. Of course there are some exceptions due to actual bullet construction/materials.

Which leads into a 1:10 twist being faster than a 1:12 twist which seems backwards untill you think about it.

Also in long range load development, "watching" the barrel move in and out of its harmonic "sweet spot" as you make the loads hotter and hotter is pretty cool. Reading about it is one thing, but seeing it in person is truely fascinating to watch.

Remind me again how a boat tail works. Haha

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8/3/2021 2:57 PM

Falcon wrote:

Here's one that my friend, who is a rifleman, just won't believe:

A bullet, upon leaving the muzzle of a gun, drops to the ...more

Hoseclamp wrote:

Only if the barrel was level right? If I shoot it up it wont be coming down for a while. If I shot it straight down off a ...more

Yes, a level barrel. The trajectory of any bullet is governed by the laws of projectile motion; essentially a parabolic curve. When the barrel is perfectly level, we can pretend the projectile is shot from the highest point of the parabola.

If it were fired upward, the bullet would travel upward until it meets the highest point, then descend. If fired downward, it is already on the descent. Note that if the barrel were to be located on the ground, yet firing upward (imagine the rest of the gun is buried,) the ascent and descent would take the same amount of time.

All the above is excepting a small amount of atmospheric friction, of course.
My friend still thinks that bullets go in a perfectly straight line for some amount of time after leaving the barrel, while gravity is suspended because of the sheer velocity of the bullet. I can't get him to agree that gravity never takes a vacation, no matter how fast something is traveling. (At least in Newtonian physics.)

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Braaapin' aint easy.

8/3/2021 3:08 PM

Falcon wrote:

Here's one that my friend, who is a rifleman, just won't believe:

A bullet, upon leaving the muzzle of a gun, drops to the ...more

Unless you are pointing the gun straight at the ground, of course........!

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8/3/2021 3:16 PM

Falcon wrote:

Here's one that my friend, who is a rifleman, just won't believe:

A bullet, upon leaving the muzzle of a gun, drops to the ...more

Hoseclamp wrote:

Only if the barrel was level right? If I shoot it up it wont be coming down for a while. If I shot it straight down off a ...more

Falcon wrote:

Yes, a level barrel. The trajectory of any bullet is governed by the laws of projectile motion; essentially a parabolic curve. ...more

This got me curious, and it seems that the fired (level) bullet would actually take longer to drop to the ground than the one just dropped from your hand. Not much, but it would definitely hit ground later. The math here seems pretty reasonable.

https://www.wired.com/2009/10/mythbusters-bringing-on-the-physics-bullet-drop/

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8/3/2021 7:36 PM

Hoseclamp wrote:

Only if the barrel was level right? If I shoot it up it wont be coming down for a while. If I shot it straight down off a ...more

Falcon wrote:

Yes, a level barrel. The trajectory of any bullet is governed by the laws of projectile motion; essentially a parabolic curve. ...more

APLMAN99 wrote:

This got me curious, and it seems that the fired (level) bullet would actually take longer to drop to the ground than the one ...more

Irrespective, we know it never went up.

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Go for it! Don't let a little thing like fear, or common sense hold you back.

8/4/2021 9:00 AM

^It looks like the math involved in the above is for bullets with air resistance, which I agree has some effect on the bullet. In a vacuum, there would be no difference.

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Braaapin' aint easy.

8/4/2021 9:19 AM

Falcon wrote:

^It looks like the math involved in the above is for bullets with air resistance, which I agree has some effect on the bullet. ...more

True, but we don't live in a vacuum.......!

cool

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