A cast saw on human skin

Steve Mould2023-11-06

yeso#sierra para yeso#piel humana#afeitadora#afeitar#cuchilla#Steve Mould#Gipssäge#Gipsverband#Gips#Haut#menschliche Haut#Slow Motion#Zeitlupe#Elektromodul

10M views|10 months ago

💫 Short Summary

The video demonstrates how a cast saw operates using slow motion footage and explains why it's safe for cutting casts but not human skin. It also shows the process of cutting through traditional plaster of Paris cast and modern fiberglass cast. The speed of sound in the skin is observed at different locations on the arm, and the Henson AL-13 razor is introduced as a well-crafted and precise shaving instrument.

✨ Highlights

📊 Transcript

✦

A cast saw is used to remove a cast, and it's designed to cut through the hard outer shell of the cast.

00:06

The saw blade is sharp and fast.

It can be dangerous if used incorrectly by someone without medical experience.

✦

A high-speed camera was used to show that a cast saw blade oscillates back and forth, cutting through the cast but not human skin.

01:16

The stroboscopic effect couldn't fake the high-speed camera due to rolling shutter artifacts.

A phantom high-speed camera that can do 2,000 frames per second in full HD was hired to capture the blade's movement.

The blade oscillates about 3mm, and a mark drawn on the blade doesn't spin but becomes blurry around the edges.

The difference in the elasticity of overinflated and underinflated balloons demonstrates why the saw can cut through the cast but not skin.

✦

Different types of casts: traditional made from plaster of Paris, and modern one with fiberglass and water-activated resin.

03:11

Plaster of Paris cast takes 24 to 48 hours to fully dry.

Fiberglass cast dries in about 15 minutes and creates less mess when cutting.

✦

The oscillating blade moves the whole cast back and forth and creates plaster shavings that float above the surface.

04:23

Traditional cast made from plaster of Paris.

Modern synthetic cast made from fiberglass and water activated resin dries much faster.

✦

Calculation of the Young's modulus of skin based on the shear modulus and Poisson's ratio.

05:19

The Poisson's ratio of human skin is about 0.48.

The Young's modulus for the back of the hand is about 100 kilopascals, and for the back of the arm is about 300 kilopascals.

✦

Promotion of Henson AL-13 razor, emphasizing its lower total cost of ownership compared to cartridge razors and its high-quality engineering.

06:56

Henson AL-13 is a family run Aerospace machine shop product.

The blade protrudes exactly 30 microns from the plane at an angle of 12 radians.

Promo code 'SteveMould' for 100 free blades with the purchase of a razor.

00:06 this is a cast saw it's used to extract

00:10 you from a cast after your bones have

00:12 healed the blades are sharp enough and

00:14 fast enough to cut through the hard

00:16 outer shell of the cast and that seems

00:19 pretty dangerous given how close the

00:21 cutting blade gets to soft human skin

00:24 parts and it would be a terrible idea

00:25 for someone with no medical experience

00:28 to attempt such a procedure on

00:30 themselves like what if my hand slipped

00:32 and the blade touched my

00:38[Music]

00:45 skin well it turns out nothing would

00:48 happen actually because a cast saw is

00:51 able to cut through a cast but it's not

00:54 able to cut through human skin to see

00:56 how that's possible we need to film it

00:57 in slow motion my first thought was that

01:00 because the movement is cyclic I could

01:02 use the stroboscopic effect to fake

01:05 having a high-speed camera like I did in

01:07 my gravitational waves video if you want

01:09 an explanation of how the stroboscopic

01:11 effect works watch to the end of that

01:13 video link in the card and the

01:14 description but when I actually tried

01:16 that the rolling shutter artifacts were

01:18 just off the charts so I hired a phantom

01:20 high-speed camera that can do 2,000

01:22 frames per second in full HD straight

01:24 away you can see that the blade isn't in

01:26 fact spinning it's oscillating backwards

01:29 and forwards and looking at the footage

01:30 it's only moving back and forth about 3

01:33 mm a tiny distance really actually you

01:36 don't need a high-speed camera to show

01:38 that if I draw a mark on the blade and

01:41 turn it on you can see the mark doesn't

01:43 spin round it becomes blurry around the

01:46 edges which tells us that it's

01:47 oscillating not spinning we'll get to

01:49 the slow motion footage of the blade on

01:51 my skin in a moment but first his a clue

01:54 as to why a cast saw can cut through a

01:57 cast but not through human skin here

01:59 here's an underinflated balloon and

02:01 here's an overinflated balloon the cast

02:03 all can't pop the underinflated balloon

02:05 but look what happens when I press it

02:07 into the overinflated balloon it pops

02:09 easily the difference is when you

02:11 overinflate a balloon you're pushing the

02:13 balloon to its elastic deformation limit

02:15 it can't stretch anymore after that so

02:17 when the teeth of the blade touches the

02:19 rubber the rubber can't stretch and move

02:21 underneath it the blade scrapes along

02:24 the rubber which cuts a hole through it

02:26 the underinflated balloon has a lot of

02:28 stretch still left in it the rubber just

02:30 moves and stretches underneath the teeth

02:33 so no hole can be cut and it turns out

02:35 that human skin is like an underinflated

02:38 balloon you can see that really clearly

02:40 here as the teeth bite into my skin they

02:43 proceed to just casually move the skin

02:46 back and forth it's fun to see the

02:48 ripples propagate outwards from the

02:50 point of contact there this is probably

02:52 a good opportunity to point out that

02:54 although you may have a tool at home

02:56 that is superficially similar to a cast

02:59 saw it may very well operate in a

03:01 different way for example it may be a

03:03 rotary tool as opposed to an oscillating

03:06 tool this Dremel is a rotating tool and

03:09 look what it does to the underinflated

03:11 balloon the rubber can only stretch so

03:13 far hopefully I got that warning out

03:15 before anyone pause the video to run and

03:17 get their angle grinder even if you know

03:19 for sure that the tool you're holding is

03:21 an oscillating tool it maybe that the

03:24 distance over which it oscillates could

03:26 be beyond the elastic deformation limit

03:28 of your skin in other words it could cut

03:30 you and in fact if the tool was sharp

03:32 enough it could cut you anyway what I'm

03:34 saying is don't try this at home I

03:36 wonder about hairs I wonder if I could

03:38 use a cast sord to shave before you find

03:41 out it's interesting to see in slow

03:43 motion how the cast saw interacts with

03:45 the different types of cast you can get

03:48 the traditional cast is made from plas

03:49 of Paris so first you put on this sleeve

03:51 then you wrap your arm in padding I mean

03:53 you don't do it the doctor does the roll

03:55 of fabric which has all this plaster of

03:57 Paris powder on it is dipped in water

03:59 water that's then wrapped around your

04:01 arm and it dries fully in 24 to 48 hours

04:05 which is quite a long time to wait but

04:07 it's really cool to see plaster of Paris

04:09 being cut in slow motion because it's

04:12 rigid the teeth of the saw scrape along

04:14 the surface of the cast chipping away

04:16 little bits of it that you can see

04:17 flying through the air another cool

04:19 thing I noticed is the oscillating blade

04:21 actually moves the whole cast back and

04:23 forth a little bit but look the plaster

04:26 of Paris shavings kind of float above

04:28 the surface while the cast Jiggles about

04:30 underneath so that's a PL of Paris cast

04:33 but if you broke your arm today they

04:34 would most likely put on a synthetic

04:37 cast like this I mean they wouldn't put

04:39 it on like this the fabric is fiberglass

04:42 and it's coated in a water activated

04:44 resin so the process starts in the same

04:46 way you dip the roll in water but once

04:48 it's applied to the arm it only takes

04:50 about 15 minutes to dry and actually it

04:52 creates much less mess when you're

04:54 cutting it off something interesting

04:55 about the waves that radiate out from

04:57 the contact point they represent the

05:00 speed of sound of my skin it's

05:02 interesting to see how the speed of

05:03 sound is different on different parts of

05:05 my arm here on the back of my arm I

05:07 estimate it's about 10 m/s but on the

05:10 back of my hand it's about 6 m/s

05:12 interestingly from that I can calculate

05:14 the shear modulus of my skin and from

05:17 that I can calculate the Young's modulus

05:19 of my skin but to get from the sheer

05:20 modulus to Young's modulus I need to

05:23 know what the pon ratio of my skin is I

05:26 talked about the pon ratio in my otics

05:28 video link in the card in the

05:30 description when I Googled Pon number of

05:32 skin I got this result the pon ratio of

05:35 cow te skin was measured uni and bi

05:38 axially and is shown to be an isotropic

05:41 and dependent on aspect ratio so there

05:43 you go but I also found out that the pon

05:45 ratio of human skin is about 0.48 and it

05:48 turns out that the Young's modulus for

05:50 the back of my hand is about 100

05:51 kilopascals and the Young's modulus for

05:53 the back of my arm is about 300

05:56 kilopascals which is good to know

06:01 I really don't like vendor lockin for

06:04 example email doesn't have vendor lockin

06:07 like I could use Gmail as my vendor you

06:09 could use Hotmail and we can still

06:11 communicate with each other whereas I

06:13 couldn't use Facebook to DM you on

06:16 Twitter because those services use

06:18 proprietary protocols that don't talk to

06:20 each other it even happens in the

06:21 physical world like I have this power

06:23 tool and a bunch of batteries that go

06:25 with the power tool but the connection

06:28 is proprietary so if I wanted to switch

06:30 to a different brand of power tool I'd

06:32 need to buy a bunch of new batteries to

06:34 go with it even razors have proprietary

06:37 connection technology so once you've

06:39 bought a particular razor handle you

06:41 have to continue buying the cartridges

06:44 from the same manufacturer but of course

06:46 there's been an open standard for razor

06:48 blades for over 200 years the safety

06:50 razor why would you buy into a

06:52 proprietary standard when you could get

06:54 a beautifully engineered safety razor

06:56 from the sponsor of this video hence and

06:57 shaving and then buy quality blades from

06:59 whoever you like for pennies compare

07:01 that to a cartridge razor where the

07:03 handle is cheap but the cartridges are

07:04 sold at a huge markup it might seem like

07:07 an economical option at the beginning

07:08 but it's a false economy the total cost

07:10 of ownership of the Henson ar-13 is

07:13 lower than a cartridge Razer after just

07:15 a few months the Henson al-13 is what

07:17 you get when a family run Aerospace

07:19 machine shop pivots to making their own

07:21 products the blade is well supported by

07:23 its all metal body it protrudes exactly

07:26 30 microns from the plane at an angle of

07:28 to on 12 radians for a really nice shave

07:31 the nice thing is you only have to buy a

07:33 new handle once a year wait once a

07:36 lifetime it's something you literally

07:38 buy once ever but what's the actual

07:41 shave like well I shaved this side of my

07:43 face with the Hensen al13 and I shaved

07:46 this side of my face with a cast saw and

07:49 the difference is unbelievable go to

07:51 Hensen shaving tocom for/ Steve mold and

07:54 use promo code Steve mold at checkout to

07:56 get 100 free blades with your purchase

07:59 of a razor just make sure both items are

08:01 in the basket when you apply the code

08:02 the link is also in the description so

08:04 check out hens and shaving today I hope

08:06 you enjoyed this video if you did don't

08:08 forget to hit subscribe and the

08:09 algorithm thinks you'll enjoy this video

08:14[Music]

08:28 next

08:30 a

💫 FAQs about This YouTube Video

1. How does a cast saw work and why is it safe for use on human skin?

A cast saw is designed to cut through the hard outer shell of a cast using sharp and fast blades. It is safe for use on human skin due to the saw's inability to cut through skin, demonstrated by the oscillating movement of the blade.

2. What are the two types of casts mentioned in the video?

The video mentions two types of casts: traditional casts made from plaster of Paris and modern synthetic casts made from fiberglass and water-activated resin.

3. What is the difference in the drying time and material between the two types of casts?

Traditional casts made from plaster of Paris take 24 to 48 hours to dry, while modern synthetic casts made from fiberglass and water-activated resin dry in about 15 minutes. The material used is also different, with the traditional cast using plaster of Paris and the modern cast using fiberglass and resin.

4. How is the speed of sound and the modulus of the skin calculated in the video?

The speed of sound and the modulus of the skin are calculated based on the waves that radiate out from the contact point. The shear modulus and Young's modulus of the skin are determined using the speed of sound and the Poisson's ratio.

5. What is the Henson AL-13 razor, and what makes it a better option than cartridge razors?

The Henson AL-13 razor is a high-quality, well-engineered razor that is considered a better option than cartridge razors due to its lower total cost of ownership and the ability to use quality blades from various manufacturers.

🎥 Related Videos