Hobbit 3 physics problem

[Aghanim]

This scene: https://youtu.be/r4xxym2tyEM?t=32s is where everyone say Legolas defies law of physics. But is it true?

From what I know, Newton's third law states that every action have equal and opposite force, so when he applies force to the falling stone, the stone exerts a reactive force that propel him upward. But he and the stone are in freefall, so when he pushes down the stone to jump, the stone might not be able to provide enough reactive force to jump. But there is mass difference between Legolas and the stone, so as Newton's second law, assuming the stone have higher mass than Legolas, the stone will be accelerated slower compared to Legolas, and so he can jump from the falling stone. But is it true or my physics is wrong?

[Technical Ben]

This. This is why I stopped watching 90% of movies released... it just... why?

[On topic]

Not really. Those rocks should then be pushed at an extremely quick rate. They still fall at the normal speed. For it to be even remotely realistic... no nothing. I have nothing. A bridge about to collapse is fine. One partially collapsed ok. But collapsed underneath you, or it's own supports at any point (clearly like nothing beneath that one), and your going down quickly.

[smjjames]

It does appear to break the laws of physics, but then again, you have to remember the setting which is a world of magic. Plus he's an elf, and so, agility and speed. Given the setting, you could handwave it off as magic really easily.

[Norpo]

It does appear to break the laws of physics, but then again, you have to remember the setting which is a world of magic. Plus he's an elf, and so, agility and speed. Given the setting, you could handwave it off as magic really easily.

I'd say this is the likely answer; Legolas has boots of +2 Physics Defying.

[RainDreamer]

Well, it is like you are inside an elevator in free fall and jump at the last moment to save yourself. You might slow yourself, but the net force is still much greater downward as gravity pulls. Unless Legolas has rocket boots or somehow managed to kick with forces that would shatter rocks (like in those anime where they flash step and fight within falling debris), it is unlikely.

However, it would be different if they are in zero G.

*note that I am not an actual scientist and may have no idea what I am talking about.

[worir4]

Guys, this is Legolas we are talking about. You have seen the scene were he takes down one of those giant elephants on his own, right?

[lajoswinkler]

Really? You're spending time questioning the portrayal of the laws of physics in a beaten-to-death ancient fantasy franchise?

Really?

[Jovus]

Wait, wait, wait.

Of all the things, all the horrible things done in that movie, that's the bit people are choosing to complain about?

[ZedNova]

He's an elf, and elves have much magic. So they can break laws of physics and use slow motion if they want to.

[Aghanim]

Yes, I do*

Back to the topic, now I understand the problem now why jumping in freefall doesn't work, so thank you and mark this thread as resolved

*Going to the nitty gritty details of the nearly non-existent magics in Middle-earth compared to other fantasy series, and with a good reason why magics isn't that apparent here, I thought that basic laws of physics still works there. And I could relate to physics problem better than other reasons why that movie is horrible

[Ralathon]

Every second legolas accumulates about 10*mass(L) of downward momentum. So he needs to dump at least that much momentum into the rocks. This depends on how fast legolas can kick rocks and how heavy those rocks are. If v(kick)*mass® = 10*mass(L) legolas will remain stationary.

This is the part where it becomes iffy. Legolas is an elf and elfs are pretty goddamn light. Just look at Fellowship of the Ring while they're trying the Caradhras mountain pass in a snowstorm. Legolas can walk on the snow without sinking away in it. So the ratio mass®/mass(L) will be very high. Therefore v(kick) can be pretty small without Legolas falling.

One additional point of consideration is that the rocks Legolas uses have an initial velocity that his feet need to match before they can transfer the momentum. Assuming a vacuum those rocks will fall at v=10*sqrt(d/5) where d is the distance from the initial bridge deck. Looks like Legolas is about 2 meters below the collapsing bridge deck, so that gives 6.3 m/s + v(kick) for legolas' feet velocity.

If Legolas is sufficiently light and sufficiently fast it could work...

[vger]

If Legolas and a shark are falling, and Legolas jumps from it, has he effectively jumped the shark?

[Tex_NL]

...

This is the part where it becomes iffy. Legolas is an elf and elfs are pretty goddamn light. Just look at Fellowship of the Ring while they're trying the Caradhras mountain pass in a snowstorm. Legolas can walk on the snow without sinking away in it. So the ratio mass®/mass(L) will be very high. Therefore v(kick) can be pretty small without Legolas falling.

That was exactly the scene that came to mind.

[Kerbart]

There's a Gary Larson (The Far Side) cartoon* where a male mosquito wearing a fedora, trenchcoat and briefcase enters his 50s style home with his wife cooking on the stove. “Work SUCKED todayâ€Â

Larson mentions that everyone seemed fine with the fact that apparently mosquitoes talk English, wear 50s outfits, have a home, cook dinner on a stove, etc. BUT OH THE HORROR OF GETTING THE FACT WRONG THAT IT'S THE FEMALE ONES THAT SUCK THE BLOOD OUT OF YOU.

Now, why am I reminded of that?

* which I can't post as it's copyrighted and Gary Larson is not Scott Adams

[Greenfire32]

If Legolas and a shark are falling, and Legolas jumps from it, has he effectively jumped the shark?

tenoutaten best post 2015

would shark again

[vger]

There's a Gary Larson (The Far Side) cartoon* where a male mosquito wearing a fedora, trenchcoat and briefcase enters his 50s style home with his wife cooking on the stove. “Work SUCKED todayâ€Â

Larson mentions that everyone seemed fine with the fact that apparently mosquitoes talk English, wear 50s outfits, have a home, cook dinner on a stove, etc. BUT OH THE HORROR OF GETTING THE FACT WRONG THAT IT'S THE FEMALE ONES THAT SUCK THE BLOOD OUT OF YOU.

Now, why am I reminded of that?

* which I can't post as it's copyrighted and Gary Larson is not Scott Adams

You know... I think this deserves some serious research.

This kind of thing is very common in fandom.

I'd like to know why I'm perfectly fine with Sankara Stones that spark to life when they're held near one another, but feel like someone's scratching on Newton's black board when Indiana Jones swings from a light fixture to land in a jeep.

[Kerbart]

The bigger question is how they make THREE three hour movies out a book of 200 pages.

[CptRichardson]

The bigger question is how they make THREE three hour movies out a book of 200 pages.

The book is REALLY, REALLY compressed.

[lajoswinkler]

The bigger question is how they make THREE three hour movies out a book of 200 pages.

Money.

[Technical Ben]

There's a Gary Larson (The Far Side) cartoon* where a male mosquito wearing a fedora, trenchcoat and briefcase enters his 50s style home with his wife cooking on the stove. “Work SUCKED todayâ€Â

Larson mentions that everyone seemed fine with the fact that apparently mosquitoes talk English, wear 50s outfits, have a home, cook dinner on a stove, etc. BUT OH THE HORROR OF GETTING THE FACT WRONG THAT IT'S THE FEMALE ONES THAT SUCK THE BLOOD OUT OF YOU.

Now, why am I reminded of that?

* which I can't post as it's copyrighted and Gary Larson is not Scott Adams

Internally consistent logic. The setup is a mosquito living as a human, not a setup of a mosquito living as a human with gender roles reversed.

It's the same with any mistake (though little) in film or writing. It's like a poor note out of an orchestra... it may be small, but someone dropping a drum or a triangle WILL be noticed and pointed out as not part of the performance.

It's silly to pretend it was part of the performance, and sadly while music understands that, other forms of entertainment do not... and seem to revel in it at times ("B" movie comedies ).

[magnemoe]

Every second legolas accumulates about 10*mass(L) of downward momentum. So he needs to dump at least that much momentum into the rocks. This depends on how fast legolas can kick rocks and how heavy those rocks are. If v(kick)*mass® = 10*mass(L) legolas will remain stationary.

This is the part where it becomes iffy. Legolas is an elf and elfs are pretty goddamn light. Just look at Fellowship of the Ring while they're trying the Caradhras mountain pass in a snowstorm. Legolas can walk on the snow without sinking away in it. So the ratio mass®/mass(L) will be very high. Therefore v(kick) can be pretty small without Legolas falling.

One additional point of consideration is that the rocks Legolas uses have an initial velocity that his feet need to match before they can transfer the momentum. Assuming a vacuum those rocks will fall at v=10*sqrt(d/5) where d is the distance from the initial bridge deck. Looks like Legolas is about 2 meters below the collapsing bridge deck, so that gives 6.3 m/s + v(kick) for legolas' feet velocity.

If Legolas is sufficiently light and sufficiently fast it could work...

The rocks are far heavier than him, add that some many blocks are still connected so we can ignore the downward push, if he pushed so hard the blocks was pushed down noticeable he would have no problems getting into safety.

We know he is fast, now add magic, the walking on snow was magic, Legolas is not heavy however he has to have an decent weight say 50-60 kg to avoid getting kicked around like as the hobbits are during fights. I say its passable in the movie, its an cool scene in an fantasy movie after all.

You can also add some time it takes for the bridge blocks to coming loose, bridge start collapsing in the center and this moves outward.

- - - Updated - - -

The book is REALLY, REALLY compressed.

Money as lajoswinkler says, its defended an bit by adding Lord of the ring content to it and some lord of the ring back story.

Lord of the ring had to be compressed even for three movies.

[Robotengineer]

I wonder if there has been a Dot Physics blog post about this. This seems like the sort of thing he would analyze.