[Youtube Review][Veritasium] 블록 사격 실험 : 해답

(Recommended)Popular Videos : [Veritasium] 블록 사격 실험 : 해답

 

This time, I will review the popular YouTube videos.

These days, even if it's good to watch on YouTube, sometimes people skip it or don't watch it if it's too long.

When you watch Youtube, do you scroll and read the comments first?

To save your busy time, why don't you check out the fun contents, summary, and empathy comments of popular YouTube videos first and watch YouTube?

(Recommended)Popular Videos : [Veritasium] 블록 사격 실험 : 해답

https://www.youtube.com/watch?v=BLYoyLcdGPc

 

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Summary Comments : [Veritasium] 블록 사격 실험 : 해답

Bi************:

In order to better measure you should use
1.  a weaker material than wood such as polystyrene
2.  a higher energy bullet
3.  a longer piece of wood (horizontally)

 

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Playtime Comments : [Veritasium] 블록 사격 실험 : 해답

Ku************:

1:34 it's reminding me of my online classes.

Lu*************:

2:31 Veritasium casually flunks the weird jump thing he did

Qu*****:

1:34 MLP reference

Ro***********:

4:08
Outside of conservation of momentum, the explanation for ALL stationary and spinning blocks rising at different heights has a few things unmentioned and left for consideration .  Everyone is assuming that all of the rounds of ammunition used in the experiment are loaded precisely identical to one another.  In reality, such is never the case due to sheer cost to the manufacturer.  They're loaded only close enough to make a combat-accurate shot every time.

The powder charges in the rounds of ammunition are loaded by weight, not by grains of powder (assuming the powder is all the same smokeless variety from the same manufacturing lot).  In order to have multiple rounds exactly (or as close as possible) the same as one another, they would have to have their casings closely inspected for perfection in their walls, their bullets closely inspected during the manufacturing process for lead/copper content and diameter (assuming the bullets are jacketed), and the powder charges loaded by number of grains rather than simply dropping in the same weight.

Getting the primers to match exactly is a whole other bag of cats to deal with.

Then there's the firearm used...   Were the chamber and barrel perfectly clean for each shot?  Was a dry barrel lubricant used?

Then there's the environment....   It'd be interesting to see this done in a lab with the firearm mounted in a perfectly vertical, perfectly stationary apparatus on a hard floor as opposed to someone's grassy back yard.

GREAT VIDEO!  I loved it!

Ye****:

1:34 lol at the guy just clicking desktop shortcuts

Sa********:

2:31 .. whooo

Mo****:

2:31

Pe***********:

Ohh, on the simulation, when it was in the center, it penetrated farther, on the sides not as much. Possibly the reason they go the same height is because since it doesn't penetrate as far on the sides is because more energy is transferred on the sides. As opposed to the middle where it penetrates farther causing more energy to be lost?

Is this a possible explanation (If he says this later in the video I dont see it im currently at 2:51)


Edit: Just remembered conservation of momentum law XD
Edit 2: I was got to where he explained when the bullet may have lost more energy in the middle and I am correct!! nevermind XD

No*******:

1:31 why is Derpy there? XD

Ja*******:

2:31

 

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Top Comments : [Veritasium] 블록 사격 실험 : 해답

Fi**:

I have a question for you here Derek :
If you consider that a rotating object ends up with more energy than a... non-rotating object, I guess.
Wouldn't a log rolling down a hill end up with more energy than a ice cube going down the same hill ? Supposing the log is a perfect cylindre and the ice has no friction at all.

Al*************:

What if the collision was elastic, e.g. rubber bullet that does not penetrate the wood. Try that, that would explain some things.

Bu************:

But if the X-ray showed the same level of penetration, then what the hell was up with the nails showing different levels of penetration...?

Se********:

The MythBusters use a medium called ballistic gel. It has served them well to test bullet depth. I think the key is to have something that is softer and so the bullet travels farther. So that 1% would be larger and therefore measurable.

De********:

Answer summary: Kinetic energy is not conserved when the collision is inelastic. The block rotating ends up having more kinetic energy than the non-rotating one. Additionally according to Newton's Second Law, with the same external force vector and same mass, it must result in the same acceleration vector.

Mi************:

big words, brain hurt, go sleep

St*************:

Omg, this was so disatisfying and satisfying at the same time.

Da****************:

 @Veritasium  What you did is simply amazing. I admire your work.

Ak*******:

Time to scale it up!

Get a block that has 10 times more mass and a bullet with 10 times more energy, and you should get a difference of about a millimeter, which, while small, is measurable.

Ma******:

Although minute, I would also like to add that while the projectile in a bullet is often consistent in weight, the powder, primer, and projectile combination can often cause fluctuations. Combined with other variables, such as a slight change in barometric pressure, gun barrel temperature (which then leads to issues of resonance) and so forth, having your projectile consistently act in the exact same way is nearly impossible. Hense why I have 1/2" groups at 100 yards instead of 0". (Yes it is the machine, not the user =D) Again, this will have very negligible effects in your experiment, but I just felt the need to point this out as an avid shooter and science enthusiast alike. Perhaps in a future experiment, you could implement a chronograph to measure velocity, and see how that affects the results. As for impact material, I'm at a loss, so far as I can tell, any material that will be soft enough to allow a significant difference in bullet depth, will likely be too soft to effectively be 'knocked' upward. The only thing that comes to mind is ballistics gel?

An******:

Hopefully those scientists planning asteroid deflection strategies watch this video...

Great job encouraging people to think scientifically and to perform their own experiments, nicely done!

si******:

make a wider block, there done

Te******:

As soon as you said "potential energy and conservation of momentum" I laughed as I got it. :D

Ri**************:

The answer is unsatisfactory largely because it wasn't testable. We have to take your word for it that the differences in sonic and heat energy accounts for the differences in total system energy. Saying that something is "unmeasurable" is not a satisfactory conclusion. 

I agree that the volume of the tunnel through the wood should have been larger in the block struck dead-on than in the block struck off-center. The difference in kinetic energy must have been the result of the differences in deformation of the block. The rotation of the block meant that the structure of the block did not need to expend as much energy stopping the bullet as it did in the first example. You might demonstrate this by using targets with greatly different levels of structural cohesiveness, perhaps harder and softer wood. Of course, then density comes into play. 

Did anyone consider that maybe the bullets did not have precisely the same amount of energy? 

I think it is interesting that the velocity of the bullet was very large, compared to the velocity of either system. The momentum of the bullet was largely due to its velocity, rather than its mass. I'm assuming that the mass of the bullet was in the same order of magnitude as the block of wood. 

Al*******:

M1V1 = M2V2.  Very nice, I got it wrong initially but once I saw it I looked at it as F=mA.  The force in the Y direction is the same in both situations, the mass is the same, so why wouldn't you expect the same acceleration in the Y direction.  Its the mistake I made all through engineering school, I didn't draw out a free body diagram.  Catching me up again after all these years.

mu***********:

What about the rotation energy of the not-so-rotating block? It rotates much less, but it's momentum of inertia is much bigger (rotating around x-axis and the longest diagonal axis) so the rotation energies might be equal.

Sc*********:

Anyone else get the urge to shoot something?

Mu***********:

this is your best video ever, why the hell did I not notice before now

Ar**********:

Veritasium, when physics turns into fun!

Ba**************:

If the difference was immeasurable, then what happened with the nail measurements?

Or were you just using different sets for comparison like you did to compare height?

Zu**************:

Try to make the blocks a little bit thicker and

in 1st case: shoot the 1st block at both the ends (equal distance from centre) at the same time with two bullets and

in 2nd case: shoot the block at only one side with both the bullets at the same time and at exactly same distance from the centre.

It might clarify if the coupling force is the real cause behind these phenomenon :) 

Vi*******:

Hi. You should try this experiment without using a bullet but something like a hammer or a spring witch hits the block from below. Because the bullet strikes a different part of the wood block and the structure of the wood varies across its lenght. Using an impact object that doesnt penetrate the wood will give you a different and more accurate answer.

th*******:

Provided that the bullet weight, and velocity at contact are the same, you should use not wood, but a material as homogeneous as possible. Increase the width of the block so that there is a larger lever arm as well. If the theory presented in the video is correct, the farther away from the center of mass the bullet hits the block, the more the block will spin causing the bullet to travel a shorter distance into the block. A material I would recommend for the block is some sort of hard rubber.

Ba*****:

oh my god. i love science. i just love how something so seemingly simple is actually  very complex and counter intuitive, and takes this wealth of knowledge to truly understand. great video.

Ni*******:

“I can’t tell you how many times I’ve hit wood with rifle” Best quote ever! Lol

Th****************:

Make the blocks out of ballistic gel...

No************:

Awesome video!!!
Now, I am not a physicist, rather, I'm simply a 1st year student of physics. but a few things I noticed with the experiment that might cause differences in results.
1. Wood was used. even if a piece of wood cut from the same 2x4 can have different densities, grain patterns, and overall mass.
2. Ammunition and firearm (my area of interest). The type of round used looked like a .22 caliber. All ammunition is inconsistent to a certain degree, but 22's are known to be more so. If a semi auto rifle was used, the gas blowback used to open the bolt is also inconsistent.
Now of course there wasn't any creation of energy lol. I simply belive the kinetic energy that was transfered from the projectile was dispersed in different ways. when shot in the center, the energy has room to evenly move throughout the block giving vertical and slight rotational motion. The block shot to the side had the same force but though instead of the majority of energy dispersing evenly throughout the block over the same time, instead it was distributing energy through 2 axis. I can only think of 2 possible reasons for the hight being similar. the first, as gravity, air density, teperature etc... remained constant, and everything else was somewhat consistent other than exact locations of shot placement, and items i meantioned earlier. having additional time in the vertical position would likely yield different results. or perform the experiment at a location that would allow the blocks of wood to reach terminal velocity, and measure the time it takes for each block to hit the ground and extrapolate the result from there. the objects going higher would hit the ground last.
the only other thing I can think of is caused from the magnus effect. but I'm not sure if it works with blocks of wood.

Th*******:

Several good answers and I'm a little late to the party but...

Given that the difference in penetration depth is expected to be very small, the obvious first answer is to increase the total travel of the bullets by lowering the density of the medium.  Lots of people are suggesting using styrofoam... which is not feasible, since the total mass of a styrofoam block that could halt a bullet would be enough that the experiment simply wouldn't work.  I've seen ballistic gel mentioned, but it lacks the rigidity to accurately model the original experiment.  I have similar objections to various other types of materials that I can think of.

One solution to these is to use a composite object.  Given that we're most interested in the end of the path through the object, you could create a block made of layers of wood of different densities.  Assuming a total penetration of approximately two inches, create a block that is composed of 1.5 inches of the original material (pine?) on the top and bottom, and replace the middle section with a lighter material like balsa wood.  Perhaps have an intermediate layer of a third type that has a density between the two  The bulk of the energy of penetration would be spent on the harder outside layer, while the "target" layer would allow the last of the penetration energy to be expended over a much longer distance.

The resultant composite block would retain rigidity and could be adjusted to more closely match the mass of the original experimental block.

Actually you could hollow out the block and fill it with ballistic gel for a similar effect.  Might still lose some of the rotational energy to pressure waves in the non-rigid gel however.  Would be an interesting experiment either way :)

Th***************:

Haah, i knew it. i left the response in previous video and i was right :) It's because of the energy that bullet loses on impact. it's common sense to me, i can virtualize it in my head so clear.

Best way to modify this test, is to use different materials. Have a metal block vs wood block, they MUST have same weight, so it means wood block has to have something heavy in the middle or metal block must have hollow points and shoot both in center. Idea of this test, is to see if they still go same height. My prediction, is that metal block will not go as high, because bullet loses a lot more energy on impact.

To clarify, you need ENERGY to punch through something, if you want bullet to go through the wood block, it requires energy to do so. So if bullet loses less energy during penetration, then it will carry the block higher. This test clearly showed that bullet that loses less energy during penetration / impact, will carry the block higher (yes it was same height, but i refer to the extra rotational energy, it had extra energy left).

 

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[Veritasium] We gathered comments about popular videos and looked at them in summary, including play time, and order of popularity.

It's a good video or channel, but if you're sad because it's too long, please leave a YouTube channel or video link and I'll post it on this blog.

 

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