this is the mechanism inside a grasshopper's leg that enables it to jump so high and it's really clever because it solves a fundamental limitation of animal muscles humans come up against the same limitation but we get around it with tools and actually it's kind of two limitations I'm going to show you how humans deal with the problem first because it's quite instructive and then we'll see how the same mechanical principles are found inside the grasshopper's body and a few different variations in other animal so here's a problem that a human might face there's an object
in the distance that I would like to puncture a hole in and I've got this little steel ball here so I think if I can get the ball going fast enough by the time it reaches that thing maybe it'll puncture a hole in it and I think well how can I do that I'm going to throw it with my arm the problem is the steel ball is quite light which means it's not offering much inertial resistance to my muscles so my hand ends up traveling really quickly and actually it takes muscles a little bit of
time to build up to their maximum force and by the time the ball has left my arm I'm nowhere near my maximum Force that's the first limitation of muscles and it's quite easy to overcome actually in quite a counterintuitive way and that is to just make the ball heavier so this ball has much more inertia so my arm is is going to move more slowly when I throw it but at least it's going to give my muscles a chance to get up to maximum force and because it's heavier it's going to have more kinetic energy
meaning when it hits the target it's going to have more puncturing ability but this is where we come up against the big limitation of muscles you can either apply a large Force slowly or a small Force at high speed and it's something you've experienced like if you've ever lifted weight if it feels heavy to you you have to lift it slowly so that makes intuitive sense but it also makes mathematical sense because what you're experiencing is your muscle maximum power output like you know that power is a measure of how quickly you can deliver energy
in other words energy divided by time but maybe you also know that energy is force times distance moved in direction of force and if we slide things around to get the force term on its own you can now see that power is also force times speed so given that your muscles have a maximum power output that explains why you can either have a small force moving quickly or a large force moving slowly but if I want either of these balls to leave my hand with enough speed to puncture the target when it arrives I need
to be applying a large Force at high speed but with my muscles I can't do both and that's where the use of tools comes in the tool in this case is a slingshot here in the UK we call it a caterp but that's a bit confusing cuz other things are called catapults so I'll keep calling it a slingshot probably the elastic of this thing is really strong so to pull it back I have to use a large Force which means I have to move my muscle slowly but that's fine because what I'm doing is I'm
storing all that energy as elastic potential energy in the slingshot and the slingshot doesn't have the same limitations as my muscles it can move with a large Force quickly so a slingshot is an example of a mechanical Power amplification device and humans have invented loads of those things another obvious example is a bow and arrow I use a large Force traveling slowly to flex the bow and that stores energy again as elastic potential energy and all that energy can be delivered by the bow with a large Force quickly one of my favorite examples is a
barbecue lighter inside there is a quartz crystal and if you hit it really hard it'll generate an electric spark these two wires carry that electric spark up to the tip where it can ignite a flame but you would never be able to hit it hard enough just like with moving your finger that short distance so instead you apply a large Force slowly right and that compresses a spring so all that energy is being stored in the spring and at some point you get far enough down that um catch is released and all the energy that's
stored in the spring is released with a large Force quickly and that's enough of a force hitting the crystal to generate the spark the hammer on a pistol works in the same way as a barbecue lighter and by the way in all these examples we're never using an external source of energy all the energy comes from your body it's just stored slowly and released quickly even the electrical energy in the spark ultimately comes from your muscles so that's what humans have figured out but what about the gra Hopper is there something like a slingshot or
an archery bow inside the grasshopper's body so here's a diagram of the back leg of a grasshopper and there are two tendons the one shown in red extends the leg so that's called the extensor tendon and the blue one flexes the leg so that's called the flexer tendon and of course each tendon is pulled by a muscle and in my model that's just these two ropes here the flexer tendon in blue the extensor tendon in red and you can see it's just a lever that pivots around this point this is the knee joint that extensor
muscle is big like amazingly in a large grasshopper like a locust that extensive muscle can produce almost 15 Newtons of force which means with both back legs at the same time a grasshopper could lift these three bags of sugar so the peak force is huge but unfortunately it takes a little while to reach Peak Force about 300 millisecond which doesn't sound like a lot but it only takes 30 milliseconds for the grasshopper to leave the ground once the jump has started so by the time the peak Force has reached there's nothing to push against that's
a bit like the issue that I had with my tricep muscle and then there's the big limitation of maximum power that we talked about earlier like a locust could bench press 3 Kg but it could only do it very very slowly and that's no use for the jump so the grasshopper needs something like a bow something that can store energy and release it quickly and this is actually something that you can see from the outside compare this jumping leg on the left with this middle leg on the right everything you can see here is exoskeleton
but the darker region is a different type of exoskeleton it's much stiffer much better for storing lots of elastic energy and you can see in this video how it bends before the kick a lot of these videos and animations come from Dr Bill heer's website by the way which has been an amazing resource for this video linking the description for that so in our model we've added a spring to represent that specialized exoskeleton I also added this lever here that's not part of the grasshopper's body that's just there to give my puny muscles enough mechanical
advantage to be able to represent the immense strength of the grasshopper's extensor muscle so here's the sequence first the flex attendant pulls the leg up and it holds it there so then when the extensor muscle contracts it's not going to cause the leg to kick out because it's being held in place by the flexor muscle in instead it's going to cause that spring to contract which remember in the case of the grasshopper is actually a super stiff specialized bit of exoskeleton that's going to bend like an Archer bow and because it's so stiff the extensor
muscle has to apply a large Force which means it has to move slowly and that's absolutely fine because what it's doing is storing up all that energy in the spring then all the grasshopper has to do is release the flexor muscle and all that gets delivered with a large Force quickly like that but that's not the whole story because the flexor muscle is much weaker than the extensor muscle like the extensor muscle can produce up to 15 Newtons of force but the flexor muscle can produce up to like 0.7 Newtons of force so how is
it that the flexa muscle is able to hold the leg in place against the much Superior force of the extensor muscle that's acting to oppose it well there's two things the first is mechanical advantage you'll notice that um the position of this tendon is much further away from the Pivot Point than this tendon here so this has mechanical advantage over this one but even that isn't enough there's actually a little bump inside the knee joint of the grasshopper and the flex attendant goes around that bump so I've put a rod here for the flex attendant
to go around so when the flexor tendon is pulled and the leg reaches this position you see how the tendon is leaving the leg almost perpendicular so almost all the force from the tendon is acting to turn the leg around the pivot whereas if you look at the angle of the extensor tendon where it meets the leg it's a shallower angle so it's only the perpendicular component of that force that acts to rotate the leg in the opposite direction around the pivot point and it's the combination of those two factors that means the much weaker
flexer muscle is able to hold the leg in place against a much stronger extensor muscle there are loads of different mechanical Power amplification mechanisms found in nature and it's really interesting to look at the different types for example the frog hopper it has one of the largest accelerations in the animal kingdom clocking in 500 G's it does that by first pulling its leg up against its chest right so imagine like the Frog Hopper's body is up here this is the chest and this is the leg that's coming up and they stick together by something akin
to Velcro so I've put some velcro there and then a muscle tries to pull the leg free but it does it via some kind of elastic thing like this so again it's a large Force applied slowly energy is being stored in that elastic medium until eventually the dark C gives way and all that energy is released with a large Force quickly the human equivalent might be something like a spud gun where you build up energy until something gives way in this case you're building up pressure until the potato seal gives way what about catch mechanisms
do you find those anywhere in nature like humans use catches a lot to hold back a large force with a catch that only requires a small Force to release and it turns out that the Trap jaw ant uses a catch mechanism to to hold its jaw open it then uses a large Force to slowly build up energy behind the jaw and then it uses a small Force to release the catch so that the jaw snap shut on the ant's prey this footage is from the ant lab by the way link to their brilliant video in
the card and description so the Trap jaw ant mechanism is not quite the same as a crossbow in the sense that the energy buildup stage happens after the catch has been put in place it's a bit like if the string of my crossbow was slack when I locked it in place and only then did I tighten up the string right this is where I get distracted by a massive side quest and I hope you'll come with me cuz it's really interesting so thinking about all these different Power amplification mechanisms I thought of one I was
like I'm sure I've seen this in a device before but I wonder if it's ever happened in nature so I printed this thing out to demonstrate it gets harder and harder to open this thing up as the elastic becomes more and more stretched but actually Beyond a certain point it gets easier again and that's because of the shallow angle of the elastic like only a small component of the force from that elastic is perpendicular to the arm so it gets easier and easier and easier until look when it passes the pivot point there it's actually
slightly holding it open now and you only need a really small Force to close it again I was sure that I'd seen a mechanism like this in a device but I just couldn't think where it was which is very frustrating I even built an alternative representation of the thing so look this is a compliant mechanism it's a by stable switch I didn't Design This by the way and look it switches between these two configurations and you need a lot of force to switch between the two stable States but look if I get it just like
halfway between the two stable States just as you're getting over that energy hump you hardly need any Force at all to move it around you know it's just as you get over the hump and then it races away to the other stable configuration but what if you put a little nub in there right so just as you're getting over the energy hump the nub in's in the way so you hardly need any Force at all to get it back to that first stable configuration and I'm pretty sure it's the same kind of thing as this
right you get just past the energy hump you know it gets easier and easier and easier you get just past the hump and then it's like on a a hair trigger but I still couldn't think of any device that employs this mechanism and then I spoke to some people if you've got any ideas please tell me because this video goes out in two days uh lots of people had ideas by the way tickets go on sale for our end of year show in a few days I'll link to that in the description a few people
said what about a mouse trap but that's not quite the same mechanism like when you're priming a mouse trap and you're pulling that thing back it gets harder and harder and harder harder and harder all the way and then you apply a catch to it so it's not the same as this right where it starts to get easier just at the end there David didn't actually suggested the lever Arch file just like the thing that I demonstrated it's hard to move at the beginning but look eventually this is mostly moving side to side so at
that point you don't need much force to move but you're not working against this spring and it would be easy to pop up if it wasn't for all that friction and it's easy to pop up Step Smith mentioned these boom cards look they pop up into a cube inside there's an elastic band and when you get towards flat there's pretty much no resistance at all because the elastic band at that point isn't really changing length but there's enough bounce in the card to get it started my favorite suggestion comes from Matt barington the compound bow
actually gets easier to pull back Beyond a certain point so it's easier to hold in that drawn position compare that experience to a normal bow where your arm is quivering with the strain of holding it at full draw that's a clever idea isn't it so it turns out that humans have used that mechanism a number of times but I don't have an example of it in nature if you can think of one let me know you know it seems to me any way you try to categorize the natural world you'll always be able to find
some exception that defies your categorical rule like the rule that mammals don't lay eggs or fish don't fly or whatever so I need to be careful because I've kind of implied that humans always do their power amplification through the use of tools and animals always use their bodies but actually I can think of an exception to both of those rules like take clicking your fingers for example try and do that directly without par amplification it's a pretty weak sound what we actually do is we press our thumb and finger together and slowly build up elastic
energy in the muscles tendons and joints and then we release it quickly and you get that snapping of the fingers there's only one known example of an animal using something external to its own body for mechanical Power amplification and that's the slingshot spider it stores elastic potential energy in its web then transfer all that energy suddenly into the web and its own body as a means of catching prey how cool is that it's interesting to see how new business models are born like during the California Gold Rush Savvy people started new businesses selling shovels but
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