Challenge Questions

This is basically a comparison of momentum and energy transfer between the bullet and the wood. Both of these quantities are conserved in the collision. It is also necessary to assume that the bullet does not strike the block of wood at a glancing angle but in a direction that is close to perpendicular to the surface of the wood. Since the rubber bullet is fairly elastic it is likely that it will bounce back from the block of wood after impact. Of course the direction that it bounces back in and by how much would depend on the mass and shape of the wood but it would be safe to say that there would be some component of the rubber bullet's velocity after the collision moving away from the block which would result in change in momentum of greater than (m X v) since v is a vector quantity. Now for the case of the aluminium bullet it is likely to penetrate the block of wood and deform during the collision but unlikely to bounce back off the block of wood making its change in momentum less than or equal to (m X v). Note that it would be equal to (m X v) if it lodged in the wood and didn't go through it. Therefore the block of wood would be imparted a larger momentum by the rubber bullet than the aluminium one.

When looking at the energy, however, the opposite is true because the kinetic energy of the bullet (1/2 X m X (v squared)) is not a vector quantity and so since the rubber bullet will have almost the same velocity after it bounces of the block of wood (assuming it is elastic and the force of the impact doesn't break its structure so that it breaks up into separate bits) very little energy will have been transferred to the block of wood. The aluminium bullet, however, will transfer much more energy because it will travel into/through the wood and will therefore have its absolute velocity reduced by a greater amount.

So the answer is that the rubber bullet will impart more momentum to the wood (therefore more likely to knock it over) but the aluminium bullet will impart more energy to the wood (therefore doing more damage to it).

To actually knock it over, wouldn't it have to hit the block above or below center mass? Otherwise it would just push the block of wood. Additionally, the amount of damge would depend on the velocity of the bullet. If a rubber bullet were traveling at several hundred thousand feet per second, it would vaporize the block, and if the aluminum bullet were traveling at 20 feet per second it would do little if any damage.

In the spirit of these types of questions it is customary to assume that there is a unique answer that uses only the information provided, ie, only depends on the material from which the bullet is made of and that all other unknown parameters are the same for both types of bullets, ie, velocity, mass, angle of impact, point of impact on wood, type of wooden block, the bullet's aerodynamic profile and resultant air resistance, etc. If these assumptions are not made then there can be no unique answer as most of the other posts have pointed out. In addition since the material from which the bullet is made is the only variable affecting the result it is also necessary to assume that there are enough differences in the properties of the materials to be able to work out a solution. While 'real life' rubber bullets may be plastic with no better elasticity than an aluminium bullet this would mean that none of the variables in the question were different and would seem contrary to the intent of the question and so I have assumed that the rubber bullet is made of a material that has significantly higher elasticity than aluminium and much less rigidity. Now with all of these assumptions you may point out that this question has no bearing on what happens in a real life situation and you may be correct (I am no expert on the properties of real rubber or aluminium bullets), however, since the person who posed the question also presumably has an answer then these assumptions are necessary to come up with a unique solution. You are correct that the probability of toppling the block depends on where the bulet hits it with respect to its centre of mass but if the location is the same for both bullets the one that imparts more momentum will have a higher chance of toppling it. Note that unless the ground on which the block is standing is frictionless it can still topple over if it is hit in its centre of mass. With respect to your comment on very high velocities, once again it is necessary to assume that the velocity is not so high as to invalidate the differences in the material properties of the bullets otherwise the intent of the question is missed.

Going back now about 50yrs ago in the UK, there was a TV show that for a stunt fired a candle from a shot gun at a wooden door, it penetrated about half way through and the candle was intact. I assume when a body is in motion each molecule has enough energy to deflect anything in it path, untill its KE is disipated, so I would say both would penetrate the wood and knock it over.

Regards JD.

The best I could find on youtube

Regards JD

Hmmm, guess you don't have these down under.

Having several 'rubber' bullets in my collection, I agree that rubber is probably the wrong term for them as they are very hard indeed, on the other hand they are not likly to enter any ones body being very blunt on the front side.

They would most defiantly knock over a block of wood. the aluminum projectile of the same shape and mass would very defiantly cause damage to the same block of wood.

Experience tells me this rather than formula.

It depends what type of 'rubber' bullet is referred to. There are probably people in Northern Ireland who can offer opinions from first hand experience, also in other countries at present. This would have been better as a discussion topic on projectiles, rather then as a 'Challenge'.

Assuming that these are travelling at the sort of speed we expect of bullets, the momentum of the "rubber" will be sufficient that it penetrates the surface of the wooden block, so neither bullet will bounce (I'm assuming that "fire at" means the collision is reasonably 'square' to the surface). That means that the overall motion of the block will be similar in both cases. Whether the block topples, slides or whatever will depend on the shape of the block, its mass, how high you hit it, the friction between block and floor, etc.

N.B. there could be some very marginal cases where the shortening of the duration of the impulse of the rubber bullet (because of its designed-in spreading) results in the block toppling for the rubber bullet when it would slide for the aluminium one - but your aim would need to be extremely steady to be certain this was the cause...

Rubber bullets would usually be bounced off the ground before hitting the target.......

First of all, we must assume that these are theoretical bullets, that the rubber is very much elastic while the aluminum is quite stiff. Then we can determine that the rubber bullet will have an elastic collision and it will knock the block around but not damage it much. The aluminum bullet will not bounce, and so it will do damage. And of course, sice I have indeed fired aluminum bullets at a block, I can verify that it does do a lot of damage. Of course we would not want to have auminum bullets because they corrode and probably damage the barrel of a real gun, unless used almost immediately. So they should only be used in physics guns, which, being theoretical, never corrode.

" is this OK"

W Ketel

I interpret the first part of the challenge wording as: which bullet is more likely to knock the wood block over - rubber/plastic or aluminum?

Depending on some factors not mentioned, the rubber bullet is more likely to bounce back than the aluminum one and hence more likely to topple the block by transferring more momentum to it. Along the same lines, the aluminum bullet is more likely to damage the wood by penetrating it.

All depends on how big the 'block' of wood is and it's dimensions.
My chopping block wouldn't fall over if you hit it with a sledge hammer.
Del

That's understandable.......

almunium damagethe wood but rubber is in spring action

Having shot many rubber bullets but no aluminum ones (correction 80mm inert grenades are made from aluminum) , thousands of FMJ and hundreds if not thousands of pointed soft points.

The rubber bullet will be shorter than the aluminum one due to higher mass density. The mass and cross section/face being the same both will bounce or penetrate about the same depending on velocity.

Soft lead will squeeze into cracks that an aluminum round would not.

The rubber bullet will deform and flow into the wood before the aluminum one would.

The aluminum will not bounce as far due to energy absorption when it deforms.

Rubber bullets pierce the skin just like FMJ but due to a much lower mass lose energy much faster but may penetrate deeper where a metal one would deform.

Very dense hard wood the aluminum will deform less and penetrate at a lower velocity

Softer woods there will be little difference.

The force the wood will react to will be the same the difference will be the aluminum will absorb energy by deforming and the hard rubber will have some elasticity reflecting some deforming energy.

This is given that rubber bullets are the same as 30 years ago.

Given a choice of the two as long as the aluminum didn't fragment I'd rather be shot with it.

If the bullet knock the wood over depend on the energy of the bullet when hits the wood. if the wood is far from the gun enough, even an atomic bomb cannt move it any mm. Haha,

the second question is , of cause, the aluminum bullet will has more stronger force than rubber bullet. no doubt.

We can use formula impulse = delta (momentum). ie. F x t = delta (momentum)

where, the end speed is zero, so delta momentum = m x v

F x t = m x v; well, as the rubber bullet has less stiffness than aluminum made, it has more act time when impact the wood. due to form change.

so that we get aluminum bullet has more force than rubber made one.

For the first question:

What is the size and mass of the wood block?

Where on the block are we shooting with respect to its center of gravity?

For the second question:

What's the shape of the bullets? Is one bullet shaped for penetration while the other for impact?

I noticed no one has mentioned the coefficient of restitution for either of these bullets. I looked for a few minutes online and I couldn't find anything either but I think you would need this number to use in the conservation of momentum before you decide the final velocity of either object. After that you can find deformation.

If I had to guess though, I would assume that the rubber bullet would cause less damage to the block.

I believe that you would have to ID the type of wood and the size and shape of the "block of wood" to get a definitive answer. A cubic foot "block" of Mangkona, Philippine Ironwood, would resist almost any handheld firearm bullets. Filipinos in the hardwood business will tell people that to cut down a 70 cm ( 27 - 28 inches)diameter Mangkono (Philippine Ironwood) tree with an axe would likely require 2 to 4 days of labor! Diamond pointed saws are usually used, with copious streams of water for blade cooling, to cut these hardwood trees. Recall the lack of effect of large caliber naval rifles in the bombardment of Japanese bunkers roofed with coconut logs during the island invasions during WW II. It would be interesting to see what a shaped charge round would do to this wood vs. steel, which would be penetrated largely via melting of the steel. The increased incidence of landslides in the Philippines from heavy rainfall is attributed to the loss of the Philippine trees to illegal cutting, and the loss of soil retention with the loss of the tress.

Presumably the difficulty of cutting is due to the silica (or something similar) in the fibres blunting the tool. That would not have significant effect on the impact of a bullet, as this does not depend on sharpness.

The answer is definitely… maybe!

Depends on a number of factors:

1. The relative mass of the block of wood vs the mass of the bullet (massive block of wood, small bullet, no; small block of wood, large bullet yes) – but also,

2. The thickness of the block (the bullet might bounce off, pass through, or be imbedded)

3. The muzzle velocity of the bullet, and

4. The hardness of the wood (large hard wood block + slow bullet, no; small hard wood block and fast bullet, yes; large soft wood block and slow bullet, maybe; small soft wood block and fast bullet, probably yes), and

5. The shape of the point of the bullet (sharp point may penetrate or shatter the block; blunt point will more likely knock the block over), and

6. The location of the impact point (if high the block will probably fall over; if low, it probably won't fall over; if in between, maybe).

7. As to how the aluminum bullet would compare to the rubber bullet, see 1 – 6.

8. As to which bullet would do more damage, see 1 – 6.

And my final answer is: if I were to shoot the bullet at the block of, I wouldn't know if the block of wood fell over because with my luck the bullet would ricochet off the block of wood and hit me, requiring an immediate trip to the hospital.

In reading the responses so far the ones dealing with the transfer of kinetic energy are the only ones close. The statement was both the bullets (rubber/plastic and aluminum) are shot with the same kinetic force. Upon impact the rubber/plastic will compress thus converting the kinetic force (energy) to potential force (energy). When the compress reverses itself the potential energy is converted back to kinetic force moving in the opposite direction, thus no splintering of the wood. The aluminum bullet does not compress anywhere near as much as the rubber/plastic so the kinetic force continues into the wood separating the wood fibers and creating damage. I could belabor with formulas but the answer is above in simple words. Handling kinetic force is the main obstacle to good armor.

My more considered answer is that the aluminium bullet is more likely to break the wood, but the rubber bullet is more likely to coat it. As regards their relative probability of knocking the block over (not specifically in the question), the answer is "it depends".

If we consider the bullet travelling close to the muzzle velocity, the forces available exceed the elastic limits of the materials. Clearly, the bullet will give on impact, and compress and spread - but it takes pressure to provide the acceleration required for the spreading, and this pressure will be sufficient to cause the bullet to penetrate the wood - at least far enough that the bullet will not bounce out. This applies both to the aluminium bullet and to the 'rubber' one - it is incidentally the same process that allows a pressure washer to work. There will be a difference between the extent to which the bullets ultimately spread, which depends on the density distribution and elastic properties of the bullets and of the wood. But, assuming bullet-type velocities, the momentum applied to the block will be the same in both cases - albeit the durations of the impulses will be marginally different.

The lower rigidity of the rubber bullet will mean that it can be travelling faster at the point where is fails to break the wood, and in this region the rubber bullet will bounce off the block - and the rubber bullet will be more likely to knock the block over. (Note that, if we consider penetrating the fibres and sticking to them, the rubber bullet will still damage the wood)

At even lower speeds, where the aluminium bullet bounces off the block without causing damage, the higher coefficient of restitution of aluminium and wood (compared with the plasticity of a 'rubber bullet') means that the aluminium bullet is more likely to knock the block over.

Referring to restitution if you mean coefficient of restitution since the discussion is hitting a block of wood then it is possible (since we have no data on the type density shape mass etc.) to have a soft target wall in which the final coefficient of restitution would actually be greater than 1 which would mean that a greater amount of kinetic energy would be imparted by the rubber ball then that of the auluminum, and thus all things being equal the rubber ball would have a greater effect on the final outcome.

I don't have much background in this but I think the only time you have a coefficient higher than 1 is when energy is generated (like in an explosion). In a collision like this, energy would only be transferred or wasted (inelastic collision).

Recent studies have clarified that COR can take a value greater than one in a special case of oblique collisions. These phenomena are due to the change of rebound trajectory of a ball caused by a soft target wall.

This question can,t be answered without having all the info, we need to know the size and shape of the block of wood!

The two bullets are defined as having the same mass, and the same size, thus they have the same density and the same kinetic energy. First, how are you going to get a rubber bullet with the same density as the aluminum? I guess it might be possible.

I would expect the rubber bullet to deform more on impact which would result in some energy being converted to heat, thus there is less energy available to damage the wood.

Another moderately defined problem to debate over, yippee.

Ok, so saying that all the pertinent undefined parameters (velocity of projectile, point and angle of impact to the block's center of mass, etc.) are equal despite the fact that they clearly cannot all be identical. The problem hinges on the only clear difference between the projectiles, elasticity. Since the rubber projectile has less elasticity it will convert more of the kinetic energy into heat than the aluminum projectile will. This will mean that it should be more likely for the aluminum projectile to damage the wood. But since the quality of the wood is also undefined and even when defined frequently very variable, this may not determine if either projectile will knock the block over. For the aluminum might cleave a chunk off the block and impart little to the remaining block piece, while the energy loss of the rubber distributes the load over a larger area and knocks the block over. Conversely, the energy lost by the rubber might reduce the energy transfer below the critical value to tip the block over. But the highly elastic aluminum projectile imparts all of the just barely sufficient energy to tip the block over.

Once again, any answer seems viable.

Assume bullet number one is solid, not hollow and made of natural rubber.

Assume bullet number two is also solid and made of pure aluminum.

Assume both bullets have the same powder charge and were fired from the same barrel.

Assume the block of wood is solid Oak and measures exactly four inches by four inches by four inches.

When bullet number 1 hits the block of wood it will transfer some of its energy and move the block a noticable ammount. The rubber bullet may leave a small impression and most likely a black mark where it struck the block of wood but it will bounce off and be difficult to find.

When bullet 2 strikes the block of wood it will penetrate the surface and move the block a significant distance. It will have transfered all or most of its energy into the wood and if not imbedded in the wood it will be found near to where the block was originally located.

The rubber bullet will resemble its former shape and condition. The aluminum bullet will be noticably disfigured.

Someone else can explain using math and technical terms.

Talk about a Challenge Question that leaves out information needed to come to a clear conclusion! We have a prime example here. Of course, in a situation like this, we have to make assumptions, and we have no way of knowing if our assumptions match what the originator of the CQ intended.

Some have mentioned the angle of impact, but no one has looked at it in depth. The only specific we are given is that the block is standing on the floor. If the question said sitting, we would imagine a block with a square profile (cube), or a rectangular profile with its long axis horizontal (i.e., domino laying flat). But the word standing implies a rectangular profile with the long axis vertical (domino standing on end). This then brings up not only the angle of impact, but the point of impact and the aspect ratio between the vertical and horizontal axes as well.

For a block with a vertical axis much longer than its horizontal axis, any point of impact above the CG will cause the block to fall over backwards, regardless of the angle. Impact below the CG might cause it to fall forward, or it might teeter for a while and either fall forward or come to rest in its original position, depending on the angle and the height of the point above the floor.

I will probably think on this some more, and draw up a few illustrations. For now, I need to put away my pot-stirring spoon.

OK, I finally had took the time to draw some illustrations of aspect ratios for the block. I chose a range of horizontal to vertical ratios of 1:1.2 to 1:2 with increments of .2.

As you can see, the 1:1.2 is close to being square, and much more stable than the taller profiles. However, I can imagine this block could be knocked over if the point of impact is close to one of the upper corners, the path of the bullet does not come near the CG, and the momentum of the bullet is sufficient to move the block.

When I get take more time, I will draw some more illustrations including the angles of impact.

I have what I think is simple answer assuming the mass of the wood is the same for both shots. The aluminum bullet would inflict the most damage because it would not absorb as much of the impact energy as the rubber bullet would.

Any bullet will split a 1 foot pieceof 2"x4" of NZ radiata pine at 10 yards and it will fall over. Are we talking about real bullets or theoretical ones I have used real bullets as a sport/hobby/job so to make a general assumtion on how the wood will react is ludicrus given the variables involved

Wood, by nature is somewhat compressible, even the hardest of woods. So anything striking it will deform it ever so slightly which can be considered damage. The bullet shape will also have a lot to do with the amount or type of damage. So the question is a bit lacking in definition.

So my answer is both, as at a high velodity, either bullet will likely deform about the same amount with most of the energy being delivered to the board..

Ball-park densities ; Wood 600(kg/M³), Rubber 1500, Plastic 1200, Aluminium 2700

A matchstick will fall over, a tree wont.

The 'rubber' bullet is designed to knock people over, so the wood may topple. Wood is fibrous, so any projectile will cause damage by compression/splitting. Rubber might bounce or ricochet, same for the others. Aluminium is about 2 to 3 times denser than plastic, and about twice as dense as rubber. In either case, the aluminium bullet will have to be hollow ("Same mass...."), and will probably get pancaked whatever it does to the wood.

I'm now going to bang my head on the table and see what happens. It's the only way I can do a control experiment without getting out of my comfy chair.

Both bullets has the same energy (mass, size, and speed), but when the rubber one hits the wood most of the energy is dissipated in deforming the bullet. While when the aluminium hits the wood;the molecular structure of the aluminium bullet helps to transmit most of the energy to the wood, breaking it and making a hole.

Hi el_indiana, you wrote: "..but when the rubber one hits the wood most of the energy is dissipated in deforming the bullet."

Maybe, but: rubber is most definitely more elastic than aluminum. If there is any bounce-back of the rubber bullet from the block, the rubber bullet will transfer more momentum to the block than a (presumably) non-bouncing ali-bullet. The delta-momentum transferred to the block will be equal to: the original momentum of the bullet minus losses during compression plus backwards momentum of the bullet.

Due to the lack of specifics, I think the only way to answer this challenge is statistically. Short of doing a Monte-Carlo analysis with a range of speeds, masses, impact points, etc., the best answer is probably that the rubber bullet is more likely to topple the block over.

Isn't statistics a saving grace? ;)

Jorrie

Yes you are correct. What I want to say is that the elastic propierty of the rubber bullet makes the energy dissipates over a bigger area than the aluminium bullet. So when the aluminium bullet hit the wood, and transfer all the energy to the wood, it is over a small area; so the pressure over that point is enormous.
But when the rubber bullet hits the wood, it gets deformed and the impact area is bigger than the aluminium bullet, so the preasure for a same area is much less.
That is why the aluminium bullet can break the wood and the rubber hardly can do it.
I hope I could be quite clear.
Have a nice day.

I have shot many (rubber) bullets into a cardboard box full of newspaper and it never penitrated the other side. Hmmmm I have never done the same w/ an alum. shot?

Looks like I have something to do tonight w/ a block of wood and some amo.

Ha ha. This is a very easy answer. It's funny to watch people over analyze. No disrespect meant of course.

Anyway...

If Both bullets had the same size, mass, and speed- then I would have to imagine that the rubber bullet (if it were truly made of rubber) would have a higher density that the aluminum- but also higher elasticity. Let's also, for argument sake, say that both rounds are not hollow point- just standard rounds.

Let's just say that both the aluminum and rubber bullets were traveling around 2300 ft/s.

Which would be around the muzzle velocity of an M16. Let's also assume the size of the wooden block... Let's say it's a 2x4.

I would say (having played around with explosives and guns all my life) at that speed, a rubber m16 round (if it were traveling 2300 ft/s) would surely penetrate the board.

But since the elasticity is higher, it would deform into a flatter and wider shape instead of shattering thereby causing more damage.

But this is only if the rubber round were to penetrate. If not, it would cause less damage than the aluminum round would- like if the board were 20 inches thick or something.

It's like the time last deer season when one of my friends shot a deer with his 30/06 and glanced it off the deer's shoulder- the bullet flattened into a disc shape and ripped a foot and a half hole in the dears stomach. Which is not what a 30/06 usually does.

Higher elasticity causes more damage, more stopping power, and a bigger exit wound. A less elastic round has better penetration, but less stopping power, and a much smaller exit wound. Those are the fundementals of choosing which round to use for personal protection or hunting.

Easy, right?

same mass AND size!? then wouldn't they have to have the same density?

Aluminum. The impact of both bullet on the block is the same, but since the rubber bullet is softer than aluminum, it is more likely to damage the wood.

1. Knock the block over? Depends on the geometry of the block, of course.

2. Aluminum? very little difference. The rubber bullet would have slightly more impact due to the resilience of rubber, whereas the aluminum would lose energy from the permanent deformation in the wood and aluminum. This also answers the last question.

When I ran the central area of North Dakota form an AON company I never anywhere would use them. Out here exactly like the manufacturer recomends, so they don't fall off.

There unfortunately will be assumptions regarding the various properties of the three components and velocity of the projectile.

There is simply too much information missing to encourage anyone to bet on his/her good answer.

How large is the block of wood. Is it rock hard maple wood or Balsa, or something in between.

Rubber is a natural material, but rubber bullets, are synthetic, and may not even have any rubber in them at all.

To cause the aluminum bullet to have the same shape, density and size as the "rubber" example the aluminum must be alloyed with heavier materials.

One may get creative with their answers, but I struggle to see just how anyone could guess at any answer and expect it not to be so controversial that it would hold up to even minute scrutiny.

Add some technical stuff to the problem and maybe you can get answers that aren't comical.

TooMuchFun

Maybe the next challenge will provide absolutely no technical information. We'll be asked if this something unspecified will work. The poser of the challenge will never refine the minuscule amount of information provided despite how politely we ask for clarification. In the end the answer will be revealed that we've all spent too much time, doing nothing. The experiment was a success!

Each to his own, but I have enjoyed the hobby of reloading my own ammunition in the past. I have cast heavy lead bullits, aluminum bullits and even the polymer type from the same substance that anyone can get from a local hardware store that is used for coating tool handles. Results were interesting! Nuff said about this subject.

And of course you are absolutely correct that sometimes folks spend TooMuchTime doing nothing.

TooMuchFun

From experience in shooting Metallic Silhouette competitions in the past, we found that three things would happen. If the bullet was a FMJ (full metal jacket), sometimes the bullet would penetrate the metal plate, creating a hole but NOT knocking the target over. If the bullet was soft lead, the bullet would stop immediately completely deforming onto the surface of the plate, and usually knocking it over. But a conventional jacketed lead tip bullet would hit the plate, and rebound off in another direction. Those had the greatest potential for knocking the plate over. Why? The FMJ went through the plate, carrying a good part of its energy along with it. Velocity did not drop to zero at impact. The lead bullet did transfer all of its energy into the plate, giving a better impact, but the most reliable was the standard jacketed that rebounded, as at impact its velocity went to zero in one vector and then was launched in a different direction with some velocity. These rounds not only dropped all their forward kinetic energy into the target, but the rebound actually increased the amount of energy transferred into the target.

So, with the two bullets you described and not knowing anything about the wood block, the aluminum bullet would tend to penetrate the wood, while the rubber bullet would tend to bounce off. Damage and penetration would go to the aluminum bullet, but actual transfer of energy (knockdown power) would go to the rubber bullet. At least that is what I have seen in thirty years of shooting experience.

At the time I was enjoying this activity I discovered that the aluminum bullet became immediately unstable and and completely missed the bullet trap impacting a cement wall and doing absolutely no damage other than leaving a small impact mark in the paint and shiny fragments about the area. The polymer bullet totally disintegrated against the 1/2 plywood panel on which I stapled the targets, with out penetration.

The hand gun was a Ruger 357 magnum, the load was placed in a 38 S&W case, packed with 2 grains of bullseye powder, the distance was 50 ft.. The mold created a standard 125 grain round nose projectile if cast using a blend of plumbers lead and wheel weights.

Given the lack of significant density and weight, I really doubt that the aluminum bullet would penetrate a wood source such as rock hard maple or locust. Further I would really be surprised if it could carry enough energy to knock over an 8"X8"X2' tall timber of either of those woods even at 50".

A 22 cal. LR round fired from a rifle at a meer 50' will penetrate only about 3/4 " into locust wood. I have personally made this observation, and it did not move the target.

I don't reload anymore. I find that buying the powder locally is just too expensive to make it worth while. I do like to shoot black powder though and I am considering the use of the "semi" smokeless powders, for reloading a few light loads for a 410 ga shotgun, just to observe the results. Must be careful to begin very light with the powder though. I don 't need to hurt myself or destroy the gun.

TMF

Stp all the nonsense lets add this and that!

Which would you rather fall on your head a 1# frozen chicken or a 1# thawed chichen. Same weight, same speed.

I don't know exactly what you mean by stop all the nonsense. Your original Blog flat sucks as it carries too little info for any one of reasonable intelligence to come to many realistic conclusion. If that is the best you can do then stick to your flying chickens and leave ballistics to those who under stand them

TMF

That's a trick question - the egg has to come first.

Hi guys. Didn't einstein sit at a desk and think up the special and general theories of relativity. That's what you guys need to do here. The answers(s) is (are) clear. There is a spectrum of answers. First, the word fire. I remember my physics teacher in high school firing the chalkboard eraser at students who talked in his class. So "firing" could be anything from a weak toss to a nuclear-enhanced hardened projectile-launched device. So we start by tossing the bullets at the block. In our mind's eye we can imagine the rubber bouncing off the block. At harder and harder throws, eventually we can see the block being knocked over. But because the aluminum is harder, it would knock the block over sooner. The rubber would elastically deform and bounce off, where at the same speed the aluminum would make a loud clunk and impart slightly more energy to the collision. The block would fall over. Now, as we increase the speeds, next the rubber would knock the block over. At higher and higher speeds, the block would continue to get knocked over. although at a certain point the aluminum would be embedded in it, and then the rubber. The next stage would be when the aluminum bullet would strike at such a huge velocity that it would pass completely through the block, making a tiny hole, deforming the wood in its path and nearly vaporising the wood. It would spend such a short period of time interacting with the block that not enough energy would be imparted to the block to knock it over. At this point the rubber would still be knocking the block over, because it would deform and flatten, increasing in diameter and imparting more energy to the block. At still higher speeds it also would pass through the block without knocking it over.

The Answer will be posted right here on CR4 on March 3rd

Blimey, Kris ! They finally put an answer up !!!!! The strange thing is, you didn't take the piss too much in order to get their attention. I know you PM'd them about the snow shadow thing when they didn't pick up on all the musical silliness, but this time it seems to have worked. They must have been waiting for another song, and in their frustration slipped up and posted the answer when one didn't appear. Hurrah ! Maybe some other gallant person PM'd them this time ?

I wonder how many people have shuffled their mortal coil while waiting for answers on these things. It'd be nice if they could send subscribers a notification when they answer does eventually appear, that way the next of kin would have some form of closure. I know, Kris, you could ask if that ever-so-nice Mr Leonard to alter the way in which it's done. He might have to haul poor Mark out of the basement to add a little bit of code, but it might be possible.

Tell ya what, Kris. Don't say anything. Just wait and see how many people are going to come back and see what the correct answer is. OK, so you haven't read it yourself yet, and you're miffed that you just knocked coffee all over your desk, but look on the bright side; Here is a whole new microsphere of CR4 activity to watch, and the cigarette ash has been washed all over your desk. The murky veneer has quite a nice effect, and it's saved you a whole bunch of time from cleaning it. You've got a great excuse not to answer the mail as it hangs up to dry.

Your ever loving chum,

Kris

ps - If you cleared all the garbage off your desk, the coffee mug wouldn't tip over. If you had a good tidy up each Friday none of this would have happened. Really, you're your own worst enemy sometimes. I dunno....tut tut.

What do you mean, "the correct answer". Dogmatic, maybe, but correct in detail - not really (though the broad conclusions were generally agreed). The aggregate of answers from participants is (IMnsHO) better than the Authorised Version.

Notes:
Rubber is softer than aluminium or wood, so we are more aware of its elastic properties. But the description of the rubber bullet "bouncing back immediately" is misleading. That would require higher force on the wood than the aluminium bullet. The rubber bullet will spread, which will reduce penetration; whether it reduces the impact time depends on how deep the aluminium bullet penetrates. Also, any rebound will be quite slow (relative to the original velocity).

As my earlier reply posted, this question as barely stated is so vague that almost any answer is plausible. If the block of wood has the same mass as a match box while the two bullets have the mass of a Volkswagen Jetta, then you will get a completely different answer than the proposed "answer."

When I see a poorly worded question, I quickly dismiss the understanding of the questioner. I certainly have no faith in this answer.

My bad - I should have said "official answer" i/o "correct answer". I can only think of a couple of occasions when the official answer has been better than any posted. Not that that's the only measure. Alternative solutions and related discussion make the whole thread worth reading. Those who just check CR4 for the question and it's given 'official' answer are missing out (and on occasion are probably left woefully misinformed). I'm quite happy with my post #53. With the given conditions, and my fertile (I wonder why it's fertile ?) imagination, I can picture the results of an experiment on this question.

I don't see anything wrong with the answer given to us, it's just boringly worded.

Fertility is usually assisted by manure. Just be careful of the origins (perhaps avoid horse*& bull) and be diligent with the weeding?

*Paradoxically, the best for the garden