# Why Woodchips?
**URL:** https://boards.straightdope.com/t/why-woodchips/22061
**Category:** Factual Questions
**Created:** [June 11, 2000, 10:32pm UTC](https://boards.straightdope.com/t/why-woodchips/22061 "2000-06-11T22:32:53Z")
**Posts on this page:** 18
**Page:** 2
### Author:  [@silenus](https://boards.straightdope.com/u/silenus)
#### Post date: [March 7, 2016, 10:58pm UTC](https://boards.straightdope.com/t/why-woodchips/22061/21 "2016-03-07T22:58:11Z")
Note: This is a 16 year old zombie.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [March 7, 2016, 11:07pm UTC](https://boards.straightdope.com/t/why-woodchips/22061/22 "2016-03-07T23:07:31Z")
Sure, but rubber isn’t very bouncy. Especially not shredded rubber.
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### Author:  [@snowthx](https://boards.straightdope.com/u/snowthx)
#### Post date: [March 7, 2016, 11:34pm UTC](https://boards.straightdope.com/t/why-woodchips/22061/23 "2016-03-07T23:34:27Z")
Zombie or not - with the current controversy unsettled for the use of ground-up rubber tires on soccer and football fields, I doubt many playgrounds will be using it for the foreseeable future.
As far as woodchips, as mentioned, sand tends to get dirty with cigarette butts, animal waste, and other detritus, and must be raked clean periodically. I suppose chips are going to be cheaper and any leaves or twigs falling into it will just become part of the mass. I am not sure about how “safe” chips are compared to other materials, tho.
In our area, which has a fire danger in the summer and fall, mind you, they decided this past holiday season to grind-up Christmas trees and are now in the process of spreading the resultant chips, twigs, and needles around the non-lawn areas around parks and alongside trails, as mulch and to reduce weeds. Did I mention we live in a fire-prone area? Aren’t dried-out Christmas trees a major fire hazard?
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### Author:  [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)
#### Post date: [March 8, 2016, 6:14am UTC](https://boards.straightdope.com/t/why-woodchips/22061/24 "2016-03-08T06:14:37Z")
Wood has anti-bacterial properties, which likely makes wood chips more sanitary. I’m not sure if that was known back when this thread was first active.
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### Author:  [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)
#### Post date: [March 8, 2016, 3:53pm UTC](https://boards.straightdope.com/t/why-woodchips/22061/25 "2016-03-08T15:53:58Z")
> [@snowthx](#):
>
> … Aren’t dried-out Christmas trees a major fire hazard?
A nice vertical drying rack of pine needles with lots of room for a chimney effect is a set-up for a conflagration in your house.
A bunch of chopped pine detritus spread on the forest floor, not so much. Anything organic burns better than dirt does, but you’re not talking about a big hazard here. What would be on that surface if not for this pine mulch?
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### Author:  [@beowulff](https://boards.straightdope.com/u/beowulff)
#### Post date: [March 8, 2016, 5:48pm UTC](https://boards.straightdope.com/t/why-woodchips/22061/26 "2016-03-08T17:48:44Z")
> [@einv](#):
>
> A poster above stated that rubber may be preferred to wood chips. This is not the case. When you fall a certain height on a surface, the amount of injury is dependent on two factors—the change in momentum and the contact time. Anything that is bouncy causes a bigger change in momentum vertically than something that is non-bouncy. Further, a smaller contact time results in a larger overall impact force. Rubber is probably the worst thing that you can fall on from a great height, as both the momentum change and contact time work against your favor.
Oh, B.S.
People are not spherical metal objects.
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### Author:  [@dracoi](https://boards.straightdope.com/u/dracoi)
#### Post date: [March 8, 2016, 6:10pm UTC](https://boards.straightdope.com/t/why-woodchips/22061/27 "2016-03-08T18:10:17Z")
> [@einv](#):
>
> A poster above stated that rubber may be preferred to wood chips. This is not the case. When you fall a certain height on a surface, the amount of injury is dependent on two factors—the change in momentum and the contact time. Anything that is bouncy causes a bigger change in momentum vertically than something that is non-bouncy. Further, a smaller contact time results in a larger overall impact force. Rubber is probably the worst thing that you can fall on from a great height, as both the momentum change and contact time work against your favor.
I don’t know how much you’re misinterpreting what the other poster said… but he’s right. The preference is actually rubber, though usually in a form that looks like wood chips or mulch from distance. Here are examples with some data sheets, laws and official recommendations on the subject: [Rubber Mulch for Playgrounds | Safe and Durable Surface Material](http://www.bestrubbermulch.com/playground-rubber-mulch.php)
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### Author:  [@Wednesday\_Evening](https://boards.straightdope.com/u/Wednesday_Evening)
#### Post date: [March 8, 2016, 7:22pm UTC](https://boards.straightdope.com/t/why-woodchips/22061/28 "2016-03-08T19:22:03Z")
Zombie or no…
My understanding was that sand was not ADA compliant whereas wood chips were. So like a good Doper I went looking for a cite…
[Playground Surfacing Materials (422KB PDF)](https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwj80dW35bHLAhWiw4MKHU5MBGAQFgggMAA&url=http%3A%2F%2Fncemch.org%2Fchild-care-health-consultants%2FPart2%2F2-4_playground_surfacing.pdf&v6u=https%3A%2F%2Fs-v6exp1-ds.metric.gstatic.com%2Fgen_204%3Fip%3D38.195.34.170%26ts%3D1457464251743337%26auth%3Dctqhbdrojii4ulksdwzkidcme5fk2zpo%26rndm%3D0.03698275681798158&v6s=2&v6t=972&usg=AFQjCNH-32tyDBi1FMSDOtkjTQqpJYoINA&sig2=3Tpgxx_K5FS9atxpwzLGNg&cad=rja)
The pdf presents pros/cons for the various playground surfaces,and whether they are ADA compliant or not. Turns out sand is only good for drops \<= 4 feet, whereas wood chips are good for up to 10 foot drops. There is also a difference between wood chips and engineered wood fiber. Wood chips are not ADA compliant, but engineered wood fiber is.
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### Author:  [@Chefguy](https://boards.straightdope.com/u/Chefguy)
#### Post date: [March 8, 2016, 8:39pm UTC](https://boards.straightdope.com/t/why-woodchips/22061/29 "2016-03-08T20:39:45Z")
Also, the notion that sand attracts cats more than other material is just nonsense. Cat’s will use pretty much any material as a cat box.
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### Author:  [@am77494](https://boards.straightdope.com/u/am77494)
#### Post date: [March 8, 2016, 9:12pm UTC](https://boards.straightdope.com/t/why-woodchips/22061/30 "2016-03-08T21:12:43Z")
For the same volume, I would think transporting sand would cost more than wood chips. Also, the fracking demand has made sand prices go through the roof.
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### Author:  [@Omar\_Little](https://boards.straightdope.com/u/Omar_Little)
#### Post date: [March 8, 2016, 9:40pm UTC](https://boards.straightdope.com/t/why-woodchips/22061/31 "2016-03-08T21:40:57Z")
> [@am77494](#):
>
> Also, the fracking demand has made sand prices go through the roof.
Pretty sure they don’t use playground sand for fracking.
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### Author:  [@Quercus](https://boards.straightdope.com/u/Quercus)
#### Post date: [March 8, 2016, 9:42pm UTC](https://boards.straightdope.com/t/why-woodchips/22061/32 "2016-03-08T21:42:02Z")
> [@einv](#):
>
> A poster above stated that rubber may be preferred to wood chips. This is not the case. When you fall a certain height on a surface, the amount of injury is dependent on two factors—the change in momentum and the contact time. Anything that is bouncy causes a bigger change in momentum vertically than something that is non-bouncy. Further, a smaller contact time results in a larger overall impact force. Rubber is probably the worst thing that you can fall on from a great height, as both the momentum change and contact time work against your favor.
I don’t know what you mean by ‘contact time’. If you mean ‘deceleration time’, then yes, a smaller deceleration time means greater force. Which is why something soft that deforms and lets the deceleration happen over a greater distance/time is better.
You’re technically right that a bounce requires more momentum change, but spreading out the change over a bigger distance/time is much more important. After all, a proper fall onto a trampoline doesn’t hurt anyone. Sure, the best thing to fall onto is something that collapses/compresses, but for a playground we also need something that can take impacts without being used up. Something that deforms easily when impacted, but then returns to its original shape. You know, something … rubbery.
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### Author:  [@robby](https://boards.straightdope.com/u/robby)
#### Post date: [March 8, 2016, 10:54pm UTC](https://boards.straightdope.com/t/why-woodchips/22061/33 "2016-03-08T22:54:08Z")
> [@einv](#):
>
> A poster above stated that rubber may be preferred to wood chips. This is not the case. When you fall a certain height on a surface, the amount of injury is dependent on two factors—the change in momentum and the contact time. Anything that is bouncy causes a bigger change in momentum vertically than something that is non-bouncy. Further, a smaller contact time results in a larger overall impact force. Rubber is probably the worst thing that you can fall on from a great height, as both the momentum change and contact time work against your favor.
> [@Quercus](#):
>
> I don’t know what you mean by ‘contact time’. If you mean ‘deceleration time’, then yes, a smaller deceleration time means greater force. Which is why something soft that deforms and lets the deceleration happen over a greater distance/time is better.
>
> You’re technically right that a bounce requires more momentum change, but spreading out the change over a bigger distance/time is much more important. After all, a proper fall onto a trampoline doesn’t hurt anyone. Sure, the best thing to fall onto is something that collapses/compresses, but for a playground we also need something that can take impacts without being used up. Something that deforms easily when impacted, but then returns to its original shape. You know, something … rubbery.
Exactly…what **Quercus** said.
The amount of injury that a person experiences in a collision is dependent on the peak forces that the person experiences. The change in momentum is not a factor, because if the change in momentum is spread out over a long enough time, the peak force experienced will be smaller. This is why I can jump into a swimming pool from a diving board without fear of injury. I wouldn’t try the same thing onto the concrete pool deck, even though the change in momentum is the same in both cases.
The contact time of the collision **is** important. Anything compressible (like rubber) is going to lengthen the contact time of the impulse (which is equal to the product of the average force times the time interval, and also equal to the change in momentum).
Another example: If you were falling, would you rather land on a trampoline or a concrete sidewalk? The trampoline does indeed result in a larger change in momentum (because your velocity changes from downward to upward), but this is vastly outweighed by the long time interval that the impulse is spread over, resulting in a smaller average force that is experienced.
On the other hand, if you land on a concrete sidewalk, your change in momentum may indeed be smaller because your final velocity is zero (assuming you don’t bounce :D), but due to the short time interval of the collision, the average force you experience is much higher.
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### Author:  [@AskNott](https://boards.straightdope.com/u/AskNott)
#### Post date: [March 9, 2016, 12:38am UTC](https://boards.straightdope.com/t/why-woodchips/22061/34 "2016-03-09T00:38:53Z")
> [@Der\_Trihs](#):
>
> Wood has anti-bacterial properties, which likely makes wood chips more sanitary. I’m not sure if that was known back when this thread was first active.
Well, it certainly isn’t anti-fungal. Wood-chip mulch carries artillery fungus. If you use it near walls or building walls, it will stain the wall a foot or more high with black mold. It also is attractive, pre-chewed snack food to termites.
Cite: [http://www.gardensalive.com/product/using-mulch-wisely](http://www.gardensalive.com/product/using-mulch-wisely)
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### Author:  [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)
#### Post date: [March 9, 2016, 1:53am UTC](https://boards.straightdope.com/t/why-woodchips/22061/35 "2016-03-09T01:53:51Z")
> [@AskNott](#):
>
> Well, it certainly isn’t anti-fungal. Wood-chip mulch carries artillery fungus. If you use it near walls or building walls, it will stain the wall a foot or more high with black mold. It also is attractive, pre-chewed snack food to termites.
Both termites and wood-eating fungus are less dangerous to humans than bacteria, though.
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### Author:  [@Lumpy](https://boards.straightdope.com/u/Lumpy)
#### Post date: [March 9, 2016, 4:00am UTC](https://boards.straightdope.com/t/why-woodchips/22061/36 "2016-03-09T04:00:31Z")
Way back when I was in grade school (sometime in the Paleozoic era), the school playgrounds were covered with what we called “strips”. They resembled shredded roof tiles and were slightly rubbery in consistency; I have no idea what they were made of.
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### Author:  [@smithsb](https://boards.straightdope.com/u/smithsb)
#### Post date: [March 9, 2016, 4:32am UTC](https://boards.straightdope.com/t/why-woodchips/22061/37 "2016-03-09T04:32:10Z")
> [@Lumpy](#):
>
> Way back when I was in grade school (sometime in the Paleozoic era), the school playgrounds were covered with what we called “strips”. They resembled shredded roof tiles and were slightly rubbery in consistency; I have no idea what they were made of.
Heh, heh. From that era the covering was probably ground asbestos, mixed with lead, mercury, and arsenic. And we liked it. And it was good for us.😃
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### Author:  [@purplehearingaid](https://boards.straightdope.com/u/purplehearingaid)
#### Post date: [March 9, 2016, 4:41am UTC](https://boards.straightdope.com/t/why-woodchips/22061/38 "2016-03-09T04:41:26Z")
> [@HorseloverFat](#):
>
> Sand just encourages the smoking kids its like standing in a giant ashtray. Woodchips do the opposite.
Dogs love to pee in the sand too so like a giant littler box too.
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