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Basically, spud guns use air pressure to shoot spuds. More air pressure, faster spud. How fast would a pineapple gun (ignore making it, say it just works) have to shoot the pineapple to be lethal?

Assume the target is your average joe who normally wear T-shirt and Shorts and maybe a hat. Not armoured soldiers.

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    $\begingroup$ Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Worldbuilding Meta, or in Worldbuilding Chat. Comments continuing discussion may be removed. $\endgroup$
    – L.Dutch
    Commented Mar 22, 2023 at 8:10
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    $\begingroup$ Something worth considering is what parts of the pineapple - you're going to get pretty nasty lacerations from the leaves. $\endgroup$ Commented Mar 22, 2023 at 12:30
  • $\begingroup$ Don't you think a strong man could simply throw a pineapple hard enough to kill, in some circumstances? $\endgroup$ Commented Mar 23, 2023 at 20:15
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    $\begingroup$ No need to fly when put on a pizza. $\endgroup$
    – CarLaTeX
    Commented Mar 29, 2023 at 8:37

5 Answers 5

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I'm going to disagree with the other answers (even though they are good answers).

The reason is because of 'Beanbag rounds' - these are less-lethal rounds fired from a Shotgun for riot control and other scenarios where you want to incapacitate someone without going for the Lethal option....

Problem is - they can be lethal. Granted they are travelling initially quite fast (300 fps) - around 200 mph, but they weigh only 40 grams and when they hit the target, they are going slower, around 130 mph with around 100 joules of energy.

Often there is an element of chance (either the victim has some underlying medical issues or the beanbag strikes a particularly vulnerable area like the throat/neck)

Plugging 100 joules of energy into the equation from Daron - a Potentially lethal pineapple (the whole pineapple) could be as low as 31 mph.

Additional info here - that uses 80 joules of energy as a potentially fatal injury to the 'correct' part of the body

However the above paper says that 80 joules to a critical area is only lethal ~35% of the time - whereas for a 95% lethality, they cite 200 joules.

So plugging that back in - a 44 mph, 1 Kilo pineapple to the head is likely to be lethal to a fit and robust adult male (20-50) in good health 95% of the time.

And I'm not gonna lie, I'm now scared of my Fruit bowl

Edit

Something I realized I had missed from my Answer - but re-reading the comments and the question should probably clarify:

My answer of 44 Mph is what speed the Pineapple needs to still be travelling at when it makes contact, not the muzzle velocity of when it leaves the SpudGun.

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    $\begingroup$ 20 mph 1 kg impact would be 40 joules. $\endgroup$
    – causative
    Commented Mar 21, 2023 at 2:16
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    $\begingroup$ Maybe. A pineapple is large and soft compared to some specific lethal non-penetrating impactors (cricket ball, baseball) described in the paper you linked. Perhaps a more apt comparison would be to a soccer ball, which is large and soft. Players intentionally will head a soccer ball weighing ~500g and traveling at 85 km/h, which is 140J. While this is not good for their long-term brain health, it doesn't kill or acutely injure them. Your pineapple carries more than 140J but I'm not sure if that's enough to make it lethal. $\endgroup$
    – causative
    Commented Mar 21, 2023 at 4:30
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    $\begingroup$ A soccer ball might also be softer than a pineapple when it comes to head injuries. I'd certainly rather have someone throw a soccer ball at my head than a pineapple, though part of that would be all the spines, which aren't relevant to lethality. The soccer ball will also bounce, while the pineapple will splatter. Probably splattering is worse, but they're both better than the projectile staying cohesive. Bouncing means the soccer ball retains a lot of kinetic energy, but increases momentum transfer to the head. Splattering also means the fragments keep some of their kinetic energy. $\endgroup$
    – causative
    Commented Mar 21, 2023 at 4:49
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    $\begingroup$ @causative - that's why I started with the Beanbag rounds from a Shotgun as my baseline comparison, as those are quite small and soft. I think a more correct explanation would be that 80 joules to the correct part of the body is enough to cause lethal trauma - such as the Trachea or other delicate areas. Certainly someone heading a ball is going to use the strongest part (typically) of their skull and would also have their Muscles tensing to help absorb the impact. There does seem to be a very large element of 'random chance' with such low energy impacts. $\endgroup$ Commented Mar 21, 2023 at 5:57
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    $\begingroup$ The mix of units is making my brain hurt. This would be so much easier to calculate and cross check in SI base units. $\endgroup$
    – Michael
    Commented Mar 21, 2023 at 9:24
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Any reasonably hard and heavy object hitting the head has the potential to kill, either directly or by causing the victim to fall and get more injuries.

A coconut may be slightly harder, but it can kill just by falling.

A hand-thrown baseball can also kill. This would be around 90 mph. This would be an upper bound on the speed, an unlucky pineapple may kill at slower speed.

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    $\begingroup$ Coincidentally, today is Brittanie Cecil's birthday. She died after getting hit by a hockey puck: en.wikipedia.org/wiki/Death_of_Brittanie_Cecil. Hockey pucks travel around 100 mph, but are probably harder than a pineapple. $\endgroup$
    – Tim
    Commented Mar 20, 2023 at 20:44
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    $\begingroup$ @Tim as speed goes up hardness matters less. You can be killed by hitting a body of water if you're going fast enough. $\endgroup$ Commented Mar 21, 2023 at 2:57
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    $\begingroup$ @MarkRansom Less, but not none, and 90 mph isn't very fast when we're talking about projectile impacts. A 90 mph baseball doesn't break when you hit it with a bat, but a 90 mph pineapple certainly would. That means that the hardness and toughness of the baseball is still a significant factor at 90 mph. Still, I agree that a 90 mph pineapple would kill. The weight makes up for the fact it is softer. $\endgroup$
    – causative
    Commented Mar 21, 2023 at 3:10
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    $\begingroup$ @causative: Ceteris paribus applies. The question is comparing the projectiles, you can't just arbitrarily change the location the projectile hits and argue that this is related to the change in projectile itself. $\endgroup$
    – Flater
    Commented Mar 21, 2023 at 5:22
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    $\begingroup$ @VictorStafusa-BozoNaCadeia There is no rule about using only SI units on this SE, as far as I know. Especially with regard to speeds, most readers would find mph or km/h (neither of which is SI) more relatable than m/s. Supplying multiple units in answers can be helpful, though. $\endgroup$
    – reirab
    Commented Mar 21, 2023 at 17:09
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As you mention, a pineapple to the head is much like a potato to the head. (Wise words). It turns out that potato cannon injuries have been studied as they relate to the speed, weight, and diameter of the potato. The formula can be easily adapted to a pineapple.

The paper analyzing potato gun injuries is, "When backyard fun turns to trauma: risk assessment of blunt ballistic impact trauma due to potato cannons" (DOI 10.1007/s00414-011-0552-y ). I'm not sure I should link to this paper because of copyright issues, but you may have heard of a "hub" where you can find such papers.

This paper uses the Sturdivan Blunt Criterion (BC) formula. BC = ln(0.5 m v^2 / (W^(1/3) * T * D)). This gives a number that correlates to injury severity.

  • m is the mass of the pineapple in kg, 1 kg
  • v is the speed of the pineapple in m/s
  • W is the mass of the target in kg. According to the paper W = 4.9 kg should be used for the head.
  • D is the diameter of the pineapple in cm. A typical pineapple has a diameter of 15 cm, but the paper mentions a corrected formula for D should be used for head impacts, so that D = 7.5 cm.
  • T is the thickness of the body wall in cm at point of impact. According to the paper T = 1 cm should be used for the head.

This would let us solve for v if we knew our desired Blunt Criterion value. For this, we can refer to "Tolerance of the skull to blunt ballistic temporo-parietal impact" (DOI 10.1016/j.forsciint.2010.10.023 ) which the potato gun paper also relies on for calculating head injury severity. According to this paper, based on the curve in Fig 9, when the BC value is 1.0, skull fracture is unlikely. When the BC value is 3.0, skull fracture is almost certain. The 50% chance of skull fracture occurs around BC = 1.7.

The potato gun paper lists four examples of head injuries from a potato gun. Three of the four involved skull fractures, but none were fatal. (In one of the four cases, the projectile remarkably was a frog rather than a potato). Also, the potato gun paper analyzed potato guns which all had head BC around 3.0. So BC=3.0 is high enough to produce a fracture but not high enough to reliably produce death. So let's pick BC=4.0 as our target.

So, we solve BC = 4.0 = ln(0.5 * 1 * v^2 / ((4.9)^(1/3) * 1 * 7.5)) for v. This gives v = 37.3 m/s, which is 83.4 mph.

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  • $\begingroup$ A pineapple is not spherical nor made of homogeneous substance. I bet that being hit perpendicularly to by its crown spikes can kill you much easily and injury you much worse than being hit by its body. $\endgroup$ Commented Mar 21, 2023 at 17:08
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    $\begingroup$ @VictorStafusa-BozoNaCadeia I doubt it. First, the crown spikes would act as fins due to their drag, so they would normally point backwards in a flying pineapple. Second, the crown spikes are just leaves - they would bend before they penetrated your skull. Certainly the spikes would be dangerous in the sense of blinding you and destroying soft tissue, but unless they can help get past the skull they don't really increase lethality. $\endgroup$
    – causative
    Commented Mar 21, 2023 at 18:16
  • $\begingroup$ For my curiosity (based on my answer) - what is the MPH value if you use a BC of 3 and then a BC of 1.5? $\endgroup$ Commented Mar 21, 2023 at 21:23
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    $\begingroup$ @TheDemonLord for BC of 1.5, the result is 10.7 m/s = 24 mph. For BC of 3, the result is 22.6 m/s = 50.5 mph. But again, based on the potato gun paper, these may cause skull fractures and injury but are unlikely to cause death. Several people have been shot in the head with potato guns with a BC of 3 but no one has died. $\endgroup$
    – causative
    Commented Mar 21, 2023 at 21:26
  • $\begingroup$ Cheers for that - those values do correlate quite nicely with the answer I gave - which was what my gut was telling me. There's probably some other factors at play as to why no one has died (thankfully) but yeah - thanks. $\endgroup$ Commented Mar 21, 2023 at 21:29
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About 100 mph.

Google says Mike Tyson can punch you in the face with 1600 Joules. This will probably kill your average Joe Schmoe if they are not prepared.

The pineapple is mostly water. Mike Tyson is mostly water. They hit about the same. So let's make them have the same energy.

The pineapple weighs about a kilo. Kinetic energy is $\frac{1}{2} mv^2$ for $m$ the mass (kg) and $v$ the velocity (m/s). Since $m=1$ we just solve

$$\frac{1}{2} v^2 = 1600 \implies v^2 = 3200 \implies v = \sqrt{3200} \simeq 57.$$

So a pineapple to the head at 60 metres per second should be plenty. That's 134 miles an hour.

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    $\begingroup$ Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Worldbuilding Meta, or in Worldbuilding Chat. Comments continuing discussion may be removed. $\endgroup$
    – L.Dutch
    Commented Mar 22, 2023 at 3:08
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Well, the weight of a pineapple is about 1 kg, and a pineapple’s volume is calculated to be about 1,000 cm3. This equates to a density of 1 g/cm3.

A typical lead slug has a density of about 11.3 g/cm3, (this being the density of lead) and strikes a target at about 480 m/s.

From this we can infer that a bullet has a density 11.3 times the density of a pineapple, and therefore our pineapple must travel at 11.3 times the speed of a bullet in order to strike its target with the same force and therefore be lethal. So, a pineapple has to be propelled at about 5424 m/s to be lethal.

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    $\begingroup$ 10,000 cubic centimeters is 10 liters. That is a typical household bucket, not a pineapple. (And you should have noticed that the relative density of a pineapple ought to be about 1, given that it is mostly water. Even cork has a relative density of about 0.2.) $\endgroup$
    – AlexP
    Commented Mar 20, 2023 at 18:07
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    $\begingroup$ Density does not matter in the way you imply it does. Comparing densities only makes sense when dealing with the same volume, as comparing the densities then gives you the comparison in mass. So you've answered what velocity a bullet-shaped pineapple would need to have the same impact as a bullet-shaped bullet (ignoring material hardness and all that); but that was not the question. $\endgroup$
    – Flater
    Commented Mar 21, 2023 at 5:30
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    $\begingroup$ I edited the answer for correcting the math and physics errors. I did not verify all the claims made. $\endgroup$
    – virolino
    Commented Mar 21, 2023 at 9:32
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    $\begingroup$ Well, he got one thing right, a pineapple travelling at 5424 mps absolutely WILL kill you. $\endgroup$ Commented Mar 21, 2023 at 10:28
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    $\begingroup$ @KimAndréKjelsberg And probably a fair bit of your surroundings, too, though perhaps not quite as much as a certain baseball. $\endgroup$ Commented Mar 21, 2023 at 12:36

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