[Youtube Review][Veritasium] 블록 사격 실험 결과

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

 

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 결과

https://www.youtube.com/watch?v=N8HrMZB6_dU

 

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Playtime Comments : [Veritasium] 블록 사격 실험 결과

Be**********:

The confused look on Destin's face at 2:09 is priceless. Pretty sure all your viewers look the same, I know I did.

H2**:

priceless at 1:46 they don't even know why they are excited!! ;p

Do**************:

1:48 ... the sound he makes is so cute!

Wi********************:

You totally broke Destin about this. That face at 2:08

Pe***:

Go to 1:02, watch the two glass pieces. The one on the right is wobbling WAY more. It's because the right side of the block exchanges energy with the right side of the glass (or whatever that material is), it's then returned back to the block after it gets a little higher. It's where the extra energy is from, and what causes the spin.

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

Please, check the video time 1:03, when you have both ascending blocks side by side for comparision.

For me, the video frame is a natural standard for the horizontal levels and to see that your red line is horizontal enough and indeed this line joins the geometrical centers of the blocks.

However, it seams to me that the support for the "nonspining" block is in a lower level (as I've said, I'm comparing to the video frame or, equivalently, to the edges of my computer's screen.

IF indeed I'm right, it means the nonspining block is raised by a higher vertical distance and so it ends up with a higher potential energy, as expected by the fact there is a rotatitonal energy for the spining block.

Of course, I'm not considering the air drag. I expect the air drag is higher for the spining block. If I'm right, this would make this block get an even lower vertical distance.

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

1:46 is that camp guy sitting on the other guy's knee?

Ma****:

2:04 clearly shows left block higher.

 

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Top Comments : [Veritasium] 블록 사격 실험 결과

Ra******:

Delta penetration = rotational energy.

Ra************:

Conservation of momentum ftw. Predicting the result using conservation of energy is doomed to failure because a lot of energy goes into putting the bullet into the block (not an elastic collision). On the off center shot, less energy goes into putting the bullet into the block... On the other hand, conservation of momentum is valid considering the incredibly short time of the collision (ignore gravity for the blink of an eye and it doesn't make a huge difference).

Of course, this is several months late...

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

The rotational energy did not seem to be that much and the height actually did look a little bit lower to me but I still think there is extra energy in the 2nd system.

To account for where that energy came from, you need to look at the bullet.  How far into the wood did it end up going?

fi******:

the block not rotating took more friction energy so is hoter than the spining one

Sh***************:

I'm guessing the missing portion of energy that went into Block A was dissipated through sound and heat at impact rather than spin.
In Block B, spin was more easily achieved, so it was easier for that energy to go into producing spin, giving off less sound and heat through friction when the bullet transfered it's energy to the block.

Mr*************:

You did not measure the heat energy of the blocks. The non-spinning block had the wood in the area of impact more compressed by the bullet, thus generating more heat.

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

I admit to answering too fast and being fooled by this one. There are two ways to understand the result. First we have to understand that the collision between the block and the bullet is completely inelastic. They don't bounce at all, but rather merge into a single unit. That means that some of the energy is lost to deformation and destruction of the wood fibers and the bullet, ultimately becoming heat. Since the off center block can respond to the collision by rotating away from the bullet's force, the bullet penetrates less deeply, and less energy is lost to inelastic heat. That energy difference goes into rotation.

Unlike kinetic and potential energy, which are not conserved when collisions are inelastic, (Think of dropping a ball of putty. All the energy goes into deforming the object.), momentum (the product of mass and velocity) is always conserved. The momentum of the system just before the collision is mV1, and the collision it is (M+m)V2, regardless of the on-center or off-center collision. V2, the velocity after the collision, will be the same in both cases, so the height will be the same in both cases.

hi*****************:

The extra energy for the rotation is simply energy that wasn't scrubbed away by friction when the bullet entered the block. 

When the bullet was fired straight into the center, an inelastic collision transferred all its momentum to the bullet-block system, which was manifest in the kinetic energy of the block's upward movement. Momentum was conserved, but ENERGY was not.

When the bullet entered off-center, the momentum exchange imparted an angular acceleration to the block. The force required to accelerate the block about it's axis of rotation is less than required to accelerate it upward, therefore the momentum exchange from the bullet to the bullet-block system scrubbed off less energy (the bullet didn't penetrate as far into the wood). The now lopsided bullet-block system now transitions from rotating about the center of the block system, to rotating about the center of the bullet-block system, which translates the remainder of the energy into the upward acceleration of the center of mass.

tr*********:

I still don't buy that they go to the same height. Consider this: The energy required to get the block spinning is small (you could get the same rotational speed using a finger) - and certainly much, much less than the energy available from the bullet. So, if 0.1% of the energy from the bullet was transformed into rotational velocity, and the other 99.9% was put into "lifting" the block, they would probably appear to go to "exactly" the same height, and you would still get the spinning effect from the off-center bullet. My prediction is that after many more experiments, we would see the off-center shots don't quite reach the same height as the center shots.

ms*:

Torque, moment or moment of force (see the terminology below), is the tendency of a force to rotate an object about an axis,[1] fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist to an object. Mathematically, torque is defined as the cross product of the lever-arm distance and force, which tends to produce rotation.
Loosely speaking, torque is a measure of the turning force on an object such as a bolt or a flywheel. For example, pushing or pulling the handle of a wrench connected to a nut or bolt produces a torque (turning force) that loosens or tightens the nut or bolt.
The symbol for torque is typically τ, the Greek letter tau. When it is called moment, it is commonly denoted M.
The magnitude of torque depends on three quantities: the force applied, the length of the lever arm[2] connecting the axis to the point of force application, and the angle between the force vector and the lever arm. In symbols:
\boldsymbol \tau = \mathbf{r}\times \mathbf{F}\,\!
\tau = \|\mathbf{r}\|\,\|\mathbf{F}\|\sin \theta\,\!
where
τ is the torque vector and τ is the magnitude of the torque,
r is the displacement vector (a vector from the point from which torque is measured to the point where force is applied),
F is the force vector,
× denotes the cross product,
θ is the angle between the force vector and the lever arm vector.
The length of the lever arm is particularly important; choosing this length appropriately lies behind the operation of levers, pulleys, gears, and most other simple machines involving a mechanical advantage.
The SI unit for torque is the newton metre (N·m). 

Je**********:

Isn't this video like 3 months old?

Re*:

NOOOO! Teach me things NOW!! D:

Ma***********:

too many variables not being totally taken into account in my opinion, though i assume the blocks themselves were at least weighed down to the milligram. Also not enough test runs to reduce the error margin regarding bullets and powder grain counts etc.. to what extent was each block of wood penetrated by the bullet, or in what specific manner did the impact crater seem to form in regards to how the energy would have vibrated throughout the block? is it regular or some type of treated wood? Additionally, it can clearly be seen that while they appear to travel the "Exact same height", they really do not. The non-spinning block travels those extra HAIRS of almost unnoticeable space. I would wager that if we were to do the math, the two would be equal in energy dissipation. The amount of energy that it would take to propel that non-spinning block those extra hairs, in my opinion would very easily be the equivalent of the energy it would take to spin the other block in free falling space for that duration. Such a small detail makes all the difference.

he*******:

So.. my guess is that in the one that doesn't spin the bullet gets lodged in deeper, making more noise and losing its energy on friction and heat in the process simply because the excess force can't go anywhere else.

Un******************:

video-ception, the video you watch is being watched inside the video your watching.

gi******:

when the spinning block is spinning the half of the block that is going up and round has posiive energy than the half that is being pulled down has negative energy so they equal 0 and the non spinning block is equal to 0 because both sides are equal to 0

Co*************:

I think they overestimate the energy that is responsible for rotating it. It looks like it has a lot of energy because it spins so fast, but the block in the air is essentially weightless because it's falling, just like astronauts are weightless because they are falling around the earth, so the energy required to get it to spin and keep it spinning isn't that big.

Le************:

hahaha minute physics got it wrong. oh the irony

Lo********:

You look like Grant from Mythbusters

Sk*******:

Is it a deja vu? I remember that he answered the question some time ago.

Ia********:

DE JA VU? I SWEAR I WATCHED THIS ALREADY XD

Re******:

There is no extra energy really, it's all about the distribution of energy.
First block hit center distributing the energy equally throughout the block.
The second block hit on the side distributed the energy equal to one side of the block and expressed the same energy in the spin of the block.

Gi******************:

Guys, in my opinion it's quite simple (and obviously after saying that I will be embarassingly wrong)
Well, you keep arguing about energy conservation, when it simply does not occur. He says explicitly that the bullet STAYS in the block, so it's an inelastic collision and there is a loss of kinetic energy. The second block doesn't gain energy out of nothing, it simply loses less kinetic energy than the first.
That said, even if energy is lost through friction (or better, it's not lost, it increases the heat of the block), linear and angular momentum are still conserved. For this reason, both the blocks gain the same speed, and reach the same height, while the second also rotates because the bullet has an initial angular momentum (relative to the center of the mass of the block) different from zero.
Thanks for reading, this is my personal thought, and I haven't looked at the correct explaination, yet.
I hope you agree with me

Br********:

This is like the fourth Veritasium video on Bullet Blocks, now.

Ga*********:

I think we are all off on this one.  The rotating block did not go as high.  If you look it seems to be slightly, very very slightly different.  The reason they look to be the same is that the rotation energy is so very very small.  Remember that kinetic energy, whether translational or rotational is dependent on the square of the velocity.  The block is spinning very slowly relative to other things, so the amount of rotational kinetic energy is very very very small, and is just not noticed in the experiment.

BC*****:

Wait a minute. I already saw this. Why is it at the top of Subscriptions again? I already saw the follow up as well... Did I travel back in time without noticing, or was the original deleted by mistake or something?

Co************:

What I'm guessing is that the efficacy of the transfer of energy was higher in the spinning one ±0.1%. That the amount of energy it takes to spin the block is that 0.1%. The amount of energy to send the block in the air at 10+m/s over coming the 9.8m/s that is the gravity of earth is 99% of the energy the bullet give and the spinning block energy is negligible. 

Ma*************:

In the rotating block the penetration of the bullet was shorter because it has "less weight on it". That's why the bullet transfered more kinetic energy instead of deforming the wood.

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

Without watching the video that explains it, and just on my own thoughts, I'd have to go with this explanation :

The "Same kinetic energy" is hokum : this is an inelastic collision, so we can't talk energy. What COUNTS is the conservation of momentum and angular momentum WITH RESPECT TO THE CENTER OF MASS.

I'm guessing that when you shoot the bullet right at the center of mass, it has momentum p. When you shoot the bullet a little to the side, it has the same momentum : p. But it now also has an angular momentum : L. Both of these must be conserved, and so the block will go as high, and it will spin.

From the energy P.O.V., the basic idea is that because both sides of the block weight it down, shooting right at the center, the block resists a lot more to the motion of the bullet that's making its way across the wood. By contrast, when you shoot it to the side, the block starts spinning, which means that the relative velocity of the bullet and the block is lower - and the bullet loses less energy to the deformation of the wood around it. Presumably, if you measured the temperature of the bullet, the one shot in the center of the block would be warmer than the one shot to the side...

ac*************:

I'm sure physicists have pointed this out in comments already but here it is: The bullet-block collision is not an elastic process. You've got energy being dissipated through the rearranging of the innards of the block, shock waves dissipating through the wood, all that jazz. So kinetic energy need not be conserved. What DOES have to be conserved is both linear and angular momentum. Both bullets have the same linear momentum, so both bullet-block systems must as well. So they take off at the same speed and rise to the same height. The offset of the second bullet from the centre of mass gives the second system an angular momentum, and that's conserved by allowing the second block to spin. Meanwhile the first system has no initial angular momentum so it does not spin. Each collision is bound by the conservation laws to produce these results; so each dissipates precisely the right amount of energy to make it so.

Fe**********:

Isn't this a pretty old video? Did we ever get an answer?

The only answer I can think of is that the bullet doesn't penetrate as far in the case with rotation, thus leaving energy left over for rotation.

Of course it could also be that there is a difference in height, but that it's negligible, and that it take more energy to overcome gravity than initiate rotation, in turn providing a counter intuitive result.

It could also be that the two bullets used wasn't exactly identically. One could easily imagine even a small amount of extra gunpowder providing the extra energy needed.

Lastly, in such an experiment it can be hard to distinguish one kind of energy from another, i.e. kinetic, gravitational, chemical, etc. and I simply do not have the expertise to make any determinations in that area.

All in all though, regardless of the result, I don't think the result is as surprising as people make it out to be. Sure it seems that there's extra energy, but all in all it is a very crude experiment and I'm sure we can agree that it takes quite a lot more energy to throw something than to spin it.


Best regards.

Ph********:

To me the spinning block didnt look to go as high at all. . But anyways the energy transutions to the dpinning block in a different way and also creates a loose pendulum which throws itself upwards.

I've not yhe patience yo do the math on a mobile phone keyboard here in comments.. talk about an exercise in frustration trying to make it format in an understandable way.. but the dpinning block mathimatically should NOT go ad high and visibly doesnt.. it ALMOST hoes as high.

The phydics are this: the bullet hits the edge of the block which imparts a set force straight up. The force is off centre of mass that is suspended on a loose fulcrum and so when the identical force to block 1 is applied upwards 2 things happen. 1 ever so briefly the nlock spins on the nail resting through it's centre (almost instantly loses contact, but it occurs). 2. The major cause if spin; yhe force is applied off centre to mass and it pushes 1 dide higher than the other, this causes 1 side to accelerate faster as surpass the other side. Since they're connected, the top spins up and around the slower side(same as a car spinning out on a slippery corner). The force though doesn't just end there though. It continues it's course around the slower side that too is also has accelerated upwards but just at a slower rate. As the faster side comes back around again it's momentum throws it again higher. One may assume that this would be cancelled ad it comes back around the otherside and throws itself downward again. But the slower side isnt staying still, ot too os movong upwards and the fadter side is piboting around it, this can be visualised as a two imposible waves with two points repeating. Point a. 2 crests of momentum amplifying movement upwards and point b. Of a node, wave a up and wave b down, close to canceling each other out. ... and so as the block spins upwards, gravily accelerates each side as they spin on it's downward stroke and slows both as it spins again as they spin upward again, acting on the entire block as a whole, the entire time. However the spinning block loses more momentum than the first centre fired block through air friction as at pushes through the air with each spin; eith not a fast enough spin and correct enough shape to create sufficient low air density above it to draw it upwards, this is a greater value of energy loss rgan in blick 1 which eas centre fired and varifies tgat the block can never ever fly as high as the first block. The blick fired at in the side flies almost as high... but still.. only almost. Everyone who clicked Not as high is CORRECT

 

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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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