I can tell you that the rotational energy is about 50% of the gravitational potential energy at the peak so I wouldn't expect its effect to be immeasurable. All will be revealed soon...

The key to the experiment is that the bullet ends up lodged inside the block in both cases. This makes the two experiments exactly equivalent as far as conservation of linear momentum. This means same vertical speed for both. The difference in rotational energy comes from the difference in deformation of the block: more penetration of the bullet in the first case means more deformation.

Hi Derek! I mentioned this before, but I will mention it again. I think that what the viewers all neglected was the energy lost in air resistance. The rotating block had less air resistance and hence loss less translational momentum than the non-rotating block. Kind of how a bullet with rifling will travel farther and straighter than a bullet without.

I hope you don't mind if I use a little of this clip in my vid

Why the hell would someone dislike this? He's just giving his two cents on the problem.

If you hit the block in the center, the energy is evenly dispursed throughout the block. that's why it has even a three dimensional spin. however, when you shoot it on the side, the energy is less evenly dispersed, and it spins because the block has to move so it moves counter clockwise in a two dimensional path. leverage. It still uses the same amount of energy to reach the same height, but one block will spin faster and one will spin in more directions or transmutate into thermal energy, etc.

Excellent comment. Different shape of the object can indeed make a huge difference. This is why the famous dimpled golf ball carries to far. One can consider a shape (like a blade or propeller) where hitting it from below will make it fly much, yes much higher. Not because of mass, but because of aerodynamics. Any impact should be considered. No matter how small, in this case Aerodynamics quite simply.

Not at all! I'm honored you want to use my response, as wrong as it is. ...I just wish I'd gone back and fixed the watermark on my video when it first went up and I saw it was cut off. Oh well.

In both blocks the bullet is stuck in the block after it hits, transferring all its vertical momentum to the blocks. As a result, the blocks start out with the same vertical speed and reach the same height. The hit deforms the blocks, so mechanical energy is not preserved, only momentum is.

Hi Derek, just a suggestion: To prove rotational energy is not tiny comparing to gravitational potential energy, maybe you can repeat the experiment with longer blocks (or block with weight attached at both ends). In such cases, I believe the two blocks would not reach the same height, because the rotational energy is more significant.

I certainly left that possibility open (at 0:50), since that's part of what happened with the tree explanation.

If i had to geuss i would say that shooting the gun on the side of the block acted as a stabilizer, so less energy was lost through out the rest of the system. From the first experiment there was a clear wobble that wasn't in the second experiment.

You do make a great point. I think to prove your point, they can do a experiment that shoot the block at the edge of the block, that should get the block spinning like hell, and I think that WILL get the block to fly to a much lower height.

My best guess is that the shot to the side has imparted more its momentum more efficiently to the blocks momentum. That is to say, more energy was lost deforming the wood with the first shot. I would be interested to see the same experiment done in a way that doesnt deform the block, a rubber bullet maybe?

I do not know why is the bullet experiment is non intuitive for lots of people. The main idea that you need to know is that the trajectory of the object being stimulated by a force can be found by assuming that the force will be applied directly to the center of the mass. Therefore in the two situations, the center of the mass should rise to the same height. It is quite an irony that the guy from minutephysics did not know this and he tries to teach physics to the people.

This is a good idea, however you are forgetting (or did not know) that rotational kinetic energy and transnational kinetic energy are independent of one another. This is demonstrated by the bullet block experiment. When an object is hit by the same force (the bullet) whether at the center of mass or not it will tend to have the same transnational kinetic energy. The rotation kinetic energy is a result of the distance from the center of mass the force was applied

I don't think energy arguments are very useful since diff amounts of energy can be lost in the inelastic collision. Instead, the bullet should have approx same vertical momentum once fired and this is preserved in the collision. The bullet block system in each case should have the same initial momentum -and mass, and velocity. Gravity exerts a constant impulse that should bring the blocks to rest in the same amount of time.

If mechanical energy was conserved then the block would go perceptibly lower. This is all about momentum conservation.

Wrong, and here is why: 1.) The rotational Energy of the Block is pretty much 2.) Since it's a inelastic shock, you wouldn't even look at it with conservation of Energy. 3.) They go up to the exact same height because of the conservation of momentum. Given that in both experiments the Bullets have the same Momentum, the Blocks will have the same Momentum right after they were hit. Therefore The blocks will have the same speed and therefore go to the same height. I'm aware that my english sucks

My thoughts as well. I am expecting a deeper cavity in the first block than the second.

Dont Try To Compare with them....These Guys are expert

Already been revealed. Expended energy in the deformation of the block.

This is a very logical approach to the answer, I am really looking forward to more feedback on this. I have an idea that the spinning motion could assist the rise of the block, like a kind of propeller, though thats a long shot,,,

He didn't try to trick us, he fooled himself. I expect he will have to backpedal some for the video.

Well, it was my best guess. I look forward to the correct answer from you!

Well it would be cool nonetheless if you could give us a few more infos about the experiment. Especially the dimensions of the blocks, their weights and how high they went.

Respect.

So you're not a fan of the law of conservation of momentum then?

I tried to tell him...

I must say these were my initial thoughts as well, but I think it should measurably lower and something else is going on that I don't understand to keep it at the same height.

I would like to see the negligent pull a fact amplified somehow. .. Same exact experiment with a longer piece of wood and more of an offset impact point.

veritasium, conservation of the momentum demands that momentum before and after the collision be the same, right? SO, speed at which both blocks are launched is the same. But amount of energy lost due to penetration in the first case is larger. In the second case we have to have rotation and part of the energy that would be lost to heat is here simply given for rotation. Potential energies are the same because masses are same and so is the initial velocity. Interplay is happening betw, rot and Q

Well done sir!

I agree with you. Thanks for elaborating!

show your calculations. you need the 1)rise height, 2)rotation rate, and 3)dimensions of the block(this is hardest and definitely required for calculating moment of inertia and thus rotational KE)

But be very embarrassing to know if you are wrong in few days..

I worked out that the rotational energy was 0.05% of the bullets KE. ~11 rotations in 69s and moment of intertia of a wooden cuboid. 0.0001m lower spinning, pretty hard to see.

10^15 is smaller than an atom by 5 orders of magnitude i think there was something wrong in ur calculations

This is right.

Your remark about the Math (maths) does not hold up because no one has done the math yet.

In the time-laps part of your video, i count 9.5 rotations of the block while it going up and down. Which allow me to calculate that the rotational energy was 5% of the potential energy at peak (see my video for the calculation). Could it be a stroboscopic effect on the video ? because with 50% of energy i should have count 26 rotations.

I did some calculations. If I am right the ratio between the rotational energy and the potential energy is not really tiny. I get about 5% by using very imprecise approximations from watching the video. This would result in a height difference of about 5 cm (or 2 inches). I think this would have been obvious in the high speed footage. Even if I approximated very badly, there is shurely not a ratio of 10^-15 or ever smaller!

This guy is cool, why is the is getting so many dislikes , he's just sharing his opinion, which is what derek wanted people to do.

Some people want to watch the world burn, and sadly, some of them have access to the internet.

Very well said!

I think its really great that you took time to point some technicalities out! There is no shame in that, infact that's what science is about! I like all of the channelsyou mentioned in his video, but I am not automatically blocking any potential to 'correct' what may seem to be a potential 'error' regardless of whether or not it ends up being an error. I would not be too confident with anybody who automatically takes anything as gospel anyway.

Look at my response video for the calculations : /watch?v=B2dpVhVm8yA On the 1080HD video 1) rise height = 733 for the 1st block and 713 for the 2nd (found 2,5% of different which match 5% of energy in the spin 2) rotation rate is 9.5 divide by the time gap for going up and down (this time gap simplify when i do the ratio) 3) dimension of the block are 80 x 110

Haha... Or, Derek tricked himself.

I dont think it has much, if anything to do with air pressure or resistance

logically this explanation makes sense, but as we see and learn time and time again, you're not really suppose to mix physics and logic together

wrong in science isn't embarrassing at all.

Exectly what i tought, i hope i wrong though

Why does no one just work it out? :S

David schwimmer?

And the practical point of this expt was?

I never ever think you cheat on us :) A real scientist never lies or says things it's not sure :)