[{"data":1,"prerenderedAt":914},["ShallowReactive",2],{"layer:human-body-anatomy:investigate":3},{"layer":4,"contentHash":895,"dependencyHashes":896,"approval":907,"releaseId":913},{"schemaVersion":5,"conceptId":6,"locale":7,"depth":8,"revision":5,"title":9,"subtitle":10,"summary":11,"objectives":12,"estimatedMinutes":18,"plate":19,"blocks":43,"sourceIds":890,"reviewStatus":891,"authoring":892},1,"human-body-anatomy","en","investigate","Predict it, then test it","Seven claims about your body, tested with paper, a tape measure and real class data","Guess before you look: does a hollow tube beat a solid rod, does height equal arm span for everyone, can a bone reveal a stranger’s height, does exercise raise every pulse equally, are you really symmetric, and does your shoulder really out-move your hip? Seven hands-on tests against real evidence.",[13,14,15,16,17],"Test whether a hollow tube resists bending better than a solid rod of the same material, and explain why.","Distinguish a rule that is true on average from a rule that is true for every individual, using real class height and arm-span data.","Use a simple ratio to estimate height from a bone length, and explain the limits of a single average formula.","Collect and compare a class’s resting and after-exercise pulse, and describe what varies and what does not.","Test your own body for bilateral symmetry and separate the roughly-symmetric outside from the deliberately lopsided inside.",36,{"title":20,"rows":21},"I",[22,25,28,31,34,37,40],{"label":23,"value":24},"Depth","Investigate (predict and test)",{"label":26,"value":27},"Reading time","About 36 minutes, plus time for the hands-on tests",{"label":29,"value":30},"Prior knowledge","Discover and Understand layers of this topic",{"label":32,"value":33},"Chapters","9",{"label":35,"value":36},"Labs","2 data labs, a body explorer, a sort game, a match game",{"label":38,"value":39},"You will need","Two A4 sheets, tape, a tape measure, a clock",{"label":41,"value":42},"Sensitivity","Exercise is mild and optional; no photographs",[44,48,51,72,101,107,110,127,133,138,143,146,151,154,218,231,281,286,291,294,307,343,355,359,364,367,378,393,397,400,421,425,430,435,438,451,488,493,504,516,521,524,528,532,587,592,595,608,612,616,638,643,646,659,690,716,722,727,732,866,869,881],{"id":45,"type":46,"markdown":47},"i-intro","prose","*Discover* showed you the map. *Understand* explained how the pieces are built. This layer does neither: it puts seven claims about your own body **to the test**. For each one, you will guess first, then measure, build or observe, and then compare your guess with what actually happened.\n\nThis is how anatomy has always really been learned — not by being told a fact, but by checking it. Every measurement here is safe, needs nothing but paper, a tape measure and a clock, and never requires you to share a number you would rather keep private.",{"id":49,"type":46,"markdown":50},"i-method","Keep one question in your head through every section: **is this always true, or just true on average?** A great deal of confusion about bodies comes from mixing those two up. A rule can be reliable for a whole class and still be wrong for any one person in it. You are about to see that happen more than once.",{"id":52,"type":53,"title":54,"items":55},"i-steps-method","steps","The same four-step test, every time",[56,60,64,68],{"title":57,"tag":58,"text":59},"Predict","before you look","Commit to a guess, in writing or out loud, before you measure or try anything. A prediction you made up afterwards teaches you nothing.",{"title":61,"tag":62,"text":63},"Test","measure, build or observe","Do the thing: make the paper columns, measure the class, apply the formula, take the pulses.",{"title":65,"tag":66,"text":67},"Compare","guess vs. evidence","Put your prediction next to what actually happened. Where do they match? Where do they not?",{"title":69,"tag":70,"text":71},"Explain","the why","A test that only says \"I was right\" or \"I was wrong\" is half finished. The useful half is working out *why* the evidence came out the way it did.",{"id":73,"type":74,"title":75,"terms":76},"i-glossary-method","glossary","Words for testing an idea",[77,81,85,89,93,97],{"term":78,"meaning":79,"example":80},"hypothesis","A testable guess about how something works, made before you collect evidence.","\"A hollow tube will resist bending better than a solid rod of the same mass\" is a hypothesis.",{"term":82,"meaning":83,"example":84},"prediction","What you expect to observe if your hypothesis is correct.","If the hypothesis about tubes is right, the paper tube should hold more books.",{"term":86,"meaning":87,"example":88},"variable","Anything in a test that can change or be changed.","The shape of the paper column, the number of books, and who is stacking them are all variables.",{"term":90,"meaning":91,"example":92},"controlled variable","Something you deliberately keep the same, so it cannot explain a difference in your result.","Using the same size and type of paper for both columns controls for the material.",{"term":94,"meaning":95,"example":96},"sample size","How many people, objects or measurements a test is based on.","A class of fifteen pupils is a small sample; a real forensic study uses thousands of skeletons.",{"term":98,"meaning":99,"example":100},"margin of error","How far a real value might reasonably be from an estimate.","A femur-based height estimate is usually stated with a margin of error of several centimetres, not as one exact number.",{"id":102,"type":103,"title":104,"eyebrow":105,"navLabel":106},"i-ch-tube","chapter","Claim 1: a hollow tube resists bending better than a solid rod of the same mass","Chapter 01","1 Hollow vs solid",{"id":108,"type":46,"markdown":109},"i-tube-recall","Your long bones, such as the femur, are hollow tubes with marrow in the middle rather than solid rods of bone all the way through. The claim, made in the *Understand* layer, was that for the **same amount of material**, a tube resists bending better than a rod. That was reasoning on paper. Now test it.",{"id":111,"type":82,"prompt":112,"options":113,"explanation":126},"i-predict-tube","You will make two paper columns from two identical sheets of A4 paper: one rolled into a tube and taped, one folded flat into a narrow strip. Both use the same amount of paper. Which do you predict will hold more books stacked on top before collapsing?",[114,117,120,123],{"id":115,"label":116},"a","The flat folded strip — flat things are always stronger",{"id":118,"label":119},"b","The tube — the same paper, shaped differently, resists more",{"id":121,"label":122},"c","Exactly the same, because it is the same paper",{"id":124,"label":125},"d","Neither will hold any weight at all","Make both and find out before reading on. Most people guess (a) or (c) — the tube result surprises almost everyone the first time they see it.",{"id":128,"type":129,"variant":130,"title":131,"markdown":132},"i-tryit-tube","callout","try_it","Build both columns and load them","You need two identical sheets of A4 paper, sticky tape, and some paperback books of a similar size.\n\n1. Roll the first sheet along its long side into a tube about 4 cm across and tape the seam. Stand it upright on a table.\n2. Fold the second sheet into a flat, narrow strip (accordion or a single flat fold about 4 cm wide) and stand it upright on its edge.\n3. Lower books onto each column one at a time, gently and centred, and count how many each one holds before it buckles.\n4. Repeat with a fresh pair if the first pair gave a close result. Small differences in rolling and folding matter.\n\nRecord both counts before reading the next block.",{"id":134,"type":129,"variant":135,"title":136,"markdown":137},"i-observation-tube","observation","What almost every class finds","The tube almost always wins, often by a wide margin — many classes get two, three or more times as many books on the tube. Rolling the same flat paper into a circular cross-section moves the material away from the centre line, which is exactly the geometry that resists bending best, the same reasoning from *Understand*: material far from the centre does more work.\n\nIf your tube lost, check the taping. A loose or overlapping seam lets the tube flatten under load before it has a chance to show what a true circular tube can do.",{"id":139,"type":129,"variant":140,"title":141,"markdown":142},"i-model-limit-tube","model_limit","A paper tube is not a femur","This test shows the geometry, not the biology. Real bone is not paper: it is a living composite of collagen and mineral, it is thickest exactly where the load is greatest, and its inner surface is not a smooth empty pipe but a lattice of spongy bone plus marrow. The paper test proves one honest point — shape alone can multiply strength for the same material — and nothing more. Do not treat the numbers of books as if they told you anything about how many kilograms a femur can bear.",{"id":144,"type":46,"markdown":145},"i-tube-everywhere","Once you notice the tube-beats-rod pattern, you start seeing it everywhere. Bamboo scaffolding, still common on Indian building sites, is strong enough to support workers and materials many storeys up precisely because bamboo grows as a hollow tube with internal cross-walls, not a solid stem. A bicycle frame is tubing, not solid bar, for the same reason it would be needlessly heavy and no stronger if it were solid. Drinking straws, kitchen foil rolls and the collarbone in your own shoulder are all, in their own way, the same trick: nature and engineers keep arriving at the same shape because the same physics rewards it every time.",{"id":147,"type":103,"title":148,"eyebrow":149,"navLabel":150},"i-ch-span","Claim 2: your height equals your arm span","Chapter 02","2 Height vs arm span",{"id":152,"type":46,"markdown":153},"i-span-recall","The Vitruvian claim from *Discover* was that height and arm span are about equal. Averaged over 15 classmates, that held up well: 148.9 cm against 149.0 cm, a gap of only 0.1 cm. But an average hides individuals. Time to look at every single person separately.",{"id":155,"type":156,"caption":157,"columns":158,"rows":163},"i-table-span-diffs","table","Arm span minus height for all fifteen pupils (a positive number means a longer arm span)",[159,160,161,162],"Pupil","Height (cm)","Arm span (cm)","Span − height (cm)",[164,169,174,177,181,184,188,191,195,196,201,204,207,210,214],[165,166,167,168],"1","138","136","-2",[170,171,172,173],"2","141","142","+1",[175,172,176,168],"3","140",[178,179,180,173],"4","144","145",[182,180,179,183],"5","-1",[185,186,187,173],"6","147","148",[189,186,190,183],"7","146",[192,193,194,173],"8","149","150",[33,194,193,183],[197,198,199,200],"10","151","153","+2",[202,203,198,183],"11","152",[205,199,206,200],"12","155",[208,206,209,173],"13","156",[211,212,213,183],"14","158","157",[215,216,217,200],"15","161","163",{"id":219,"type":82,"prompt":220,"options":221,"explanation":230},"i-predict-span","Looking at the table, did every single pupil have an arm span within 2 cm of their own height?",[222,224,226,228],{"id":115,"label":223},"Yes — 15 out of 15, all of them",{"id":118,"label":225},"No — about half of them",{"id":121,"label":227},"No — only two or three of them",{"id":124,"label":229},"It is impossible to tell from a table","**Yes.** All 15 of the 15 pupils fall within 2 cm either way, even though individual differences range from -2 cm to +2 cm — a spread of 4 cm. The rule is not exact for anyone, but it is close for everyone in this class.",{"id":232,"type":233,"component":234,"componentVersion":5,"config":235,"objective":274,"textAlternative":275,"help":276},"i-lab-data-span","interactive","data-lab",{"datasets":236,"valueRange":263,"step":5,"challenges":266},[237,254],{"label":160,"unit":238,"values":239},"cm",[240,241,242,243,244,245,245,246,247,248,249,250,251,252,253],138,141,142,144,145,147,149,150,151,152,153,155,158,161,{"label":161,"unit":238,"values":255},[256,242,257,244,243,258,259,247,246,250,248,251,260,261,262],136,140,148,146,156,157,163,{"min":264,"max":265},120,175,[267,270],{"measure":268,"target":246,"prompt":269},"mean","Nudge one arm span value so the class mean arm span becomes 149 cm without changing any height.",{"measure":271,"target":272,"prompt":273},"range",15,"Bring the range of heights down to 15 cm by adjusting only the shortest and tallest values. How many values did you have to touch?","Test the height-equals-arm-span rule pupil by pupil, not just on the class average.","The lab plots height and arm span as two aligned dot plots, one dot per pupil, so you can compare the same person's two measurements directly instead of only comparing two averages.\n\nDrag any dot and watch both the individual gap and the class mean update. Try to make the means exactly equal (they start 0.1 cm apart) without making every individual gap zero — you will find you can, because the small pluses and minuses in the individual differences cancel out when averaged. That cancellation is exactly why the class mean matches the rule far better than most individuals do.",{"simplerExplanation":277,"hints":278},"Two rows of dots: one for height, one for arm span, matched pupil by pupil. Move a dot and see the class average change without every person becoming exactly equal.",[279,280],"Look for the pupil with the biggest gap. Are they unusually tall, unusually long-armed, or both?","A rule can be true \"on average\" while being slightly wrong for every single case. That is not a contradiction.",{"id":282,"type":129,"variant":283,"title":284,"markdown":285},"i-nuance-average","nuance","What \"true on average\" actually means","A rule that is \"true on average\" is not a weaker version of a fact — it is a different kind of claim altogether. It says: *if you add up the differences across many people, the pluses and minuses roughly cancel out.* It does **not** say every person matches exactly, and it does not say the rule was measured wrong.\n\nThis shows up everywhere once you look for it: the average Indian household size, the average rainfall in a month, the average mark in a test. Each one is a true, useful number that describes a group and describes almost nobody in it exactly.",{"id":287,"type":103,"title":288,"eyebrow":289,"navLabel":290},"i-ch-handspan-unit","Claim 3: measuring with your hand is just as good as measuring with a ruler","Chapter 03","3 Hand-span units",{"id":292,"type":46,"markdown":293},"i-handspan-intro","Long before rulers were standardised, people measured length with parts of their own body: a **hand span** (thumb tip to little-finger tip), a **cubit** (elbow to fingertip), a **foot**. A classroom desk measured in hand spans should give roughly the same answer for everyone — or should it?",{"id":295,"type":82,"prompt":296,"options":297,"explanation":306},"i-predict-handspan","A 120 cm desk is measured in hand spans by 15 pupils with hand spans from 16 cm to 22 cm. Will they all report the same number of hand spans for the same desk?",[298,300,302,304],{"id":115,"label":299},"Yes, because it is the same desk",{"id":118,"label":301},"No — pupils with bigger hands will count fewer, bigger spans",{"id":121,"label":303},"No — pupils with bigger hands will count more, smaller spans",{"id":124,"label":305},"It is impossible to say without knowing their heights","**(b).** A bigger hand span covers more of the desk with each measure, so it takes fewer of them to reach the end. The desk has not changed length; the *unit* measuring it has changed size from person to person.",{"id":308,"type":156,"caption":309,"columns":310,"rows":313},"i-table-handspan-desk","The same 120 cm desk, measured in each pupil’s own hand spans",[311,312],"Hand span (cm)","Desk in that pupil’s hand spans",[314,317,320,321,324,325,326,329,330,331,332,335,336,339,340],[315,316],"16 cm","7.5",[318,319],"17 cm","7.1",[318,319],[322,323],"18 cm","6.7",[322,323],[322,323],[327,328],"19 cm","6.3",[327,328],[327,328],[327,328],[333,334],"20 cm","6.0",[333,334],[337,338],"21 cm","5.7",[337,338],[341,342],"22 cm","5.5",{"id":344,"type":345,"title":346,"problem":347,"steps":348,"help":353},"i-we-handspan","worked_example","The same desk, two very different-looking answers","One pupil has a 16 cm hand span; another has a 22 cm hand span. How many hand spans does each report for the same 120 cm desk, and by how much do their answers differ?",[349,350,351,352],"Smaller hand: 120 ÷ 16 = **7.5 spans**.","Bigger hand: 120 ÷ 22 = **5.5 spans**.","Difference: 7.5 − 5.5 = **2.0 spans**, for the exact same desk.","Neither pupil made a mistake. The desk is one fixed length; the unit each of them used was not.",{"simplerExplanation":354},"A bigger hand measures fewer, bigger spans. A smaller hand measures more, smaller spans. Same desk, different-looking number.",{"id":356,"type":129,"variant":283,"title":357,"markdown":358},"i-nuance-standard-units","Why the world eventually agreed on the centimetre","A hand span is instantly available and needs no equipment, which is exactly why ancient measurers used it. But it fails at the one job a unit must do: **stay the same everywhere, for everyone.** A trader in one town and a trader in another, each measuring cloth in their own hand spans, could disagree about a sale without either one lying.\n\nThe centimetre solves this by being defined once, centrally, and copied exactly onto every ruler and tape measure in the world. It is less convenient than your own hand — you have to go and fetch one — but it never changes size from person to person. This is precisely the trade-off every standard unit makes: give up personal convenience, gain universal agreement.",{"id":360,"type":103,"title":361,"eyebrow":362,"navLabel":363},"i-ch-forensic","Claim 4: a single bone can reveal a person’s height","Chapter 04","4 Estimate from a bone",{"id":365,"type":46,"markdown":366},"i-forensic-intro","Forensic anthropologists — scientists who study skeletons to learn about the people they belonged to — regularly estimate a missing person's height from just one long bone, most often the femur. The idea rests on the fact used in *Discover*: the femur is reliably about 26% of a person's standing height. Turn that ratio around and a bone becomes a height.",{"id":368,"type":345,"title":369,"problem":370,"steps":371,"help":376},"i-we-forensic","From femur to height, and back again","A recovered femur measures 45 cm. Estimate the height of the person it belonged to.",[372,373,374,375],"Start from the rule: femur ≈ height × 0.267.","Rearrange it: height ≈ femur ÷ 0.267.","Put in the number: height ≈ 45 ÷ 0.267 = **168.5 cm**.","Check it the other way: 168.5 cm × 0.267 = 45.0 cm, close to the 45 cm we started with. ✓",{"simplerExplanation":377},"If the femur is always about a quarter plus a bit of your height, then dividing the femur length by that same fraction gets you back to the height.",{"id":379,"type":380,"itemId":381,"prompt":382,"check":383,"hints":387,"feedback":390},"i-practice-forensic","practice","human-body-anatomy.investigate-femur-height","A femur measures 40 cm. Using height ≈ femur ÷ 0.267, estimate the person's height in cm to one decimal place.",{"kind":384,"answer":385,"tolerance":386,"unit":238},"number",149.8,0.2,[388,389],"Divide 40 by 0.267.","You should get a number a little under 150.",{"correct":391,"incorrect":392},"Correct: 40 ÷ 0.267 ≈ **149.8 cm**.","40 ÷ 0.267 ≈ 149.8 cm.",{"id":394,"type":129,"variant":140,"title":395,"markdown":396},"i-model-limit-femur","One ratio does not fit every body","The 0.267 figure is an **average ratio**, built from measuring many skeletons. Real forensic work is more careful than the single formula used here: the true ratio differs slightly between men and women, between populations, and even between the left and right femur of the same skeleton, so professional tables use several different equations and give a **range**, not a single number, along with a stated margin of error.\n\nThe lesson is the same one from the arm-span investigation: a formula built from averages will be somewhat wrong for almost everyone it is applied to, and a responsible scientist always says by how much.",{"id":398,"type":46,"markdown":399},"i-forensic-uses","This is not a classroom curiosity. Forensic anthropologists use exactly this kind of reasoning, made far more rigorous, to help identify people after disasters, to help archaeologists estimate the height and age of people who lived thousands of years ago from their remains, and to help police work out basic facts about an unidentified skeleton before other evidence narrows things further. The single ratio used above is the seed of a real, respected profession.",{"id":401,"type":402,"tone":403,"items":404},"i-spec-skeleton-clues","spec","neutral",[405,409,413,417],{"label":406,"big":407,"value":408},"Height","from a limb bone","A long bone such as the femur, applied to a calibrated ratio, gives height within several centimetres.",{"label":410,"big":411,"value":412},"Age, in children","from teeth","The number and type of teeth present narrows a child’s age closely, because teeth appear in a predictable order.",{"label":414,"big":415,"value":416},"Still growing?","from growth plates","An X-ray showing open growth plates means the skeleton is still lengthening; fused plates mean adult height has been reached.",{"label":418,"big":419,"value":420},"An old injury","from healed bone","A healed fracture leaves a permanent thickened mark on the bone that can still be seen and dated years later.",{"id":422,"type":423,"prompt":424},"i-reflect-forensic","reflection","A single femur estimated a stranger's height to within a few centimetres, using nothing but one ratio and one measurement. What does that tell you about how much information is quietly stored in the proportions of your own skeleton? Can you think of another single measurement (a foot, a hand, a skull) that might let you estimate something else about a person?",{"id":426,"type":103,"title":427,"eyebrow":428,"navLabel":429},"i-ch-pulse","Claim 5: exercise raises everyone’s pulse by the same amount","Chapter 05","5 Pulse and exercise",{"id":431,"type":129,"variant":432,"title":433,"markdown":434},"i-careful-exercise","careful","Keep this mild and optional","This activity uses gentle movement only — about twenty star jumps or a minute of jogging on the spot — never anything exhausting. Anyone who would rather not take part, or who has been told by a doctor to avoid exertion, should simply sit out and can still work with the class data below. Stop immediately and tell an adult if anyone feels dizzy, breathless in an unusual way, or unwell.",{"id":436,"type":46,"markdown":437},"i-pulse-setup","Measure your resting pulse for 15 seconds and multiply by 4. Then do twenty star jumps (or skip this and use the recorded numbers below), sit down immediately, and measure your pulse again the same way.",{"id":439,"type":82,"prompt":440,"options":441,"explanation":450},"i-predict-pulse","Before looking at any data: do you expect every single person’s pulse to rise by roughly the same number of beats per minute after the same mild exercise?",[442,444,446,448],{"id":115,"label":443},"Yes, almost exactly the same rise for everyone",{"id":118,"label":445},"No — everyone’s pulse will rise, but by quite different amounts",{"id":121,"label":447},"No — some people’s pulse will actually fall",{"id":124,"label":449},"It depends only on how tall the person is","**(b) is what real classes find.** Everyone's pulse goes up after exercise — that direction is reliable — but the *size* of the rise varies a great deal between people, for reasons including fitness, how hard they actually exercised, and simple day-to-day variation.",{"id":452,"type":233,"component":234,"componentVersion":5,"config":453,"objective":482,"textAlternative":483,"help":484},"i-lab-data-pulse",{"datasets":454,"valueRange":473,"step":5,"challenges":476},[455,466],{"label":456,"unit":457,"values":458},"Resting pulse (bpm)","bpm",[459,460,461,462,463,459,464,461,460,462,463,461,459,465,461],72,76,80,84,88,92,96,{"label":467,"unit":457,"values":468},"Pulse after mild exercise (bpm)",[464,464,469,465,470,464,471,469,464,465,472,469,463,471,471],104,116,100,108,{"min":474,"max":475},60,130,[477,479],{"measure":268,"target":471,"prompt":478},"Adjust the after-exercise data so its mean is exactly 100 bpm.",{"measure":271,"target":480,"prompt":481},20,"Bring the range of the after-exercise pulses down to 20 bpm. Which two pupils did you have to change?","Compare resting and after-exercise pulse for the same fifteen pupils, and test whether the rise is the same for everyone.","Two aligned dot plots: resting pulse (mean 81.3 bpm) and pulse straight after mild exercise (mean 98.9 bpm). Every single dot moved upward — nobody's pulse fell — but by very different amounts: from as little as 4 bpm to as much as 28 bpm, a range of 24 bpm in the rise itself.\n\nDrag dots and watch the class mean rise (17.6 bpm on average) stay steady even while individual rises vary hugely — the same \"true on average, not for every individual\" pattern as the arm-span data.",{"simplerExplanation":485,"hints":486},"Two sets of dots for the same fifteen people: pulse before and after mild exercise. Everyone rises, but not by the same amount.",[487],"Find the smallest riser and the biggest riser. What might explain the difference — fitness, effort, or just normal variation?",{"id":489,"type":129,"variant":490,"title":491,"markdown":492},"i-aha-heart-response","aha","A rising pulse is your heart answering a real question","Your heart is cardiac muscle, and cardiac muscle needs more oxygen-carrying blood delivered to your whole body the moment your skeletal muscles start working harder. It has no way to \"add more muscle\" in the moment, so it does the only two things available to it: beat faster, and beat a little harder. That is the entire reason a pulse rises with exercise.\n\nThe class figures make the size of the response concrete: on average, twenty star jumps raised pulse by about **17.6 beats per minute**, though the true number for any one pupil ranged all the way from 4 to 28.",{"id":494,"type":345,"title":495,"problem":496,"steps":497,"help":502},"i-we-pulse-percent","Turn the class rise into a percentage","The class mean pulse rose from 81.3 bpm resting to 98.9 bpm after mild exercise. What was that rise as a percentage of the resting pulse?",[498,499,500,501],"Find the rise: 98.9 − 81.3 = **17.6 bpm**.","Divide the rise by the starting value: 17.6 ÷ 81.3.","Multiply by 100 to make it a percentage: **21.6%**.","So twenty star jumps raised this class’s average pulse by a little over a fifth of its resting value.",{"simplerExplanation":503},"A percentage rise always compares the size of the change with the size you started from, not with any fixed number.",{"id":505,"type":380,"itemId":506,"prompt":507,"check":508,"hints":511,"feedback":513},"i-practice-pulse-rise","human-body-anatomy.investigate-pulse-rise","One pupil’s resting pulse was 88 bpm and their pulse after mild exercise was 116 bpm. By how many beats per minute did it rise?",{"kind":384,"answer":509,"tolerance":510,"unit":457},28,0,[512],"Subtract the resting value from the after value.",{"correct":514,"incorrect":515},"Correct: 116 − 88 = **28 bpm**, the biggest rise recorded in this class’s data.","116 − 88 = 28 bpm.",{"id":517,"type":103,"title":518,"eyebrow":519,"navLabel":520},"i-ch-symmetry","Claim 6: your left and right sides are mirror images","Chapter 06","6 Test your own symmetry",{"id":522,"type":46,"markdown":523},"i-symmetry-recall","*Discover* claimed humans are bilaterally symmetric on the outside. \"Symmetric\" is doing a lot of work in that sentence. Roughly symmetric, or exactly symmetric? Measure yourself and find out.",{"id":525,"type":129,"variant":130,"title":526,"markdown":527},"i-tryit-symmetry","Measure both sides of yourself","Using a ruler or tape measure:\n\n1. Measure your left hand span (thumb tip to little-finger tip, hand spread flat) and then your right hand span. Compare them.\n2. Measure the length of your left foot and your right foot, heel to longest toe, standing normally.\n3. If you can, measure the distance from the centre of your nose to the outer corner of your left eye, and again to the outer corner of your right eye.\n\nWrite down every pair of numbers before reading on.",{"id":529,"type":129,"variant":135,"title":530,"markdown":531},"i-observation-symmetry","Close, but almost never identical","Most people find their two hand spans and two foot lengths differ by only a few millimetres — close enough that you would call yourself symmetric in everyday speech, but not exactly equal under a careful ruler. A small, genuine difference like this is completely normal and is not a sign that anything is wrong; nobody is built from an exact mirror.\n\nOne pattern worth noticing without making too much of it: a dominant hand (the one you write with) is very slightly more used than the other, which over years can make its bones and muscles fractionally more developed. The skeleton you are born with sets the plan; a lifetime of use fine-tunes it slightly.",{"id":533,"type":233,"component":534,"componentVersion":5,"config":535,"objective":580,"textAlternative":581,"help":582},"i-lab-sort-symmetry","sort-game",{"prompt":536,"bins":537,"items":547,"seconds":510},"Sort each body feature by how symmetric you would expect careful measurement to find it.",[538,541,544],{"id":539,"label":540},"very","Very close to identical",{"id":542,"label":543},"roughly","Roughly matching, small differences",{"id":545,"label":546},"not","Not symmetric at all",[548,552,556,560,564,568,572,576],{"id":549,"label":550,"bin":542,"why":551},"hand-span","Left hand span vs right hand span","Usually within a few millimetres, but genuinely almost never exactly equal.",{"id":553,"label":554,"bin":542,"why":555},"foot-length","Left foot length vs right foot length","Close, though many people have one foot fractionally longer — which is why trying on both shoes matters.",{"id":557,"label":558,"bin":542,"why":559},"eye-position","Distance from nose to each eye","Faces look symmetric at a glance but are measurably slightly uneven; that is normal for every human face.",{"id":561,"label":562,"bin":539,"why":563},"rib-count","Number of ribs on the left side vs the right side","Twelve pairs, one on each side, matched exactly in almost everyone.",{"id":565,"label":566,"bin":545,"why":567},"heart-position","Position of the heart","The heart is a single organ that leans to the left. There is no matching organ on the right at all.",{"id":569,"label":570,"bin":545,"why":571},"liver-stomach","Liver on one side, stomach on the other","Two completely different organs occupy the left and right of the upper belly. It is asymmetric by design.",{"id":573,"label":574,"bin":545,"why":575},"lung-lobes","Number of lobes in the left lung vs the right lung","2 on the left, 3 on the right — a genuine, deliberate difference caused by the heart taking up room.",{"id":577,"label":578,"bin":542,"why":579},"kidney-height","Height of the left kidney vs the right kidney","Both present and similar in size, but the right one sits a little lower because the liver crowds the space above it.","Decide, feature by feature, whether the body is truly symmetric, roughly symmetric, or deliberately lopsided.","Eight features and three bins. This game rewards exactly the distinction the chapter is making: outward, paired body parts tend to be *roughly* symmetric — close but not identical under a ruler — while single internal organs are either exactly matched in number (ribs) or deliberately asymmetric by position and design (heart, liver, lungs).\n\nA wrong drop explains which of the three bins is correct and why, so a mistake is never a dead end.",{"simplerExplanation":583,"hints":584},"For each body feature, ask: is there a copy of it, and if so, is the copy in exactly the same place doing exactly the same thing?",[585,586],"Anything you can measure with a ruler on the outside of yourself is usually \"roughly\", never \"very\" or \"not\".","Single central organs that are not doubled at all still count as \"not symmetric\": there is nothing to compare them with.",{"id":588,"type":103,"title":589,"eyebrow":590,"navLabel":591},"i-ch-jointrange","Claim 7: your shoulder moves further than your hip, even though both are ball-and-socket","Chapter 07","7 Joint range test",{"id":593,"type":46,"markdown":594},"i-jointrange-recall","*Understand* explained that the shoulder and hip are both ball-and-socket joints, but built with opposite priorities: a shallow shoulder socket for reach, a deep hip socket for load-bearing stability. That was a claim about design. Time to test what it actually predicts about how far each joint can move.",{"id":596,"type":82,"prompt":597,"options":598,"explanation":607},"i-predict-jointrange","Standing straight, which do you predict you can lift higher out to the side without bending your body: a straight arm, or a straight leg?",[599,601,603,605],{"id":115,"label":600},"The arm — much higher, often close to overhead",{"id":118,"label":602},"The leg — much higher",{"id":121,"label":604},"Both about equally high",{"id":124,"label":606},"Neither can move sideways at all","**The arm, by a wide margin.** Nearly everyone can lift a straight arm out to the side well above shoulder height, close to vertical. Lifting a straight leg sideways much past waist height, without leaning the trunk to help, is difficult or impossible for most people — exactly what a shallow, mobile socket versus a deep, stable one would predict.",{"id":609,"type":129,"variant":130,"title":610,"markdown":611},"i-tryit-jointrange","Measure the two ranges, roughly","Work with a partner, standing side-on to a wall marked with clock positions is not required — a rough estimate is enough.\n\n1. Stand straight. Keeping your arm straight and your body still, lift it out to the side as high as it will comfortably go. Have your partner judge, roughly, how close it gets to horizontal (shoulder height) and then to vertical (straight overhead).\n2. Now, holding a wall or chair for balance, keep your leg straight and lift it out to the side as high as it will comfortably go, without leaning your trunk. Have your partner judge how close it gets to horizontal (hip height).\n3. Compare the two. Do not force either movement or bounce — stop well within a comfortable range.",{"id":613,"type":129,"variant":135,"title":614,"markdown":615},"i-observation-jointrange","A large, consistent gap","Most people can raise a straight arm to somewhere between shoulder height and fully overhead — commonly 150 to 180 degrees from hanging by the side. Raising a straight leg sideways to shoulder-equivalent height (full horizontal, 90 degrees) without leaning is unusual even for trained athletes; a comfortable, unforced range for most people is well under that.\n\nThe gap is not a fitness difference between your arm and your leg. It is the joint design itself: a shallow socket set free to move in exchange for stability, a deep socket set stable in exchange for range — precisely the trade-off named in *Understand*.",{"id":617,"type":380,"itemId":618,"prompt":619,"check":620,"hints":632,"feedback":635},"i-practice-jointrange","human-body-anatomy.investigate-joint-range","Both the shoulder and the hip are ball-and-socket joints, yet the shoulder moves through a far bigger range. What explains this?",{"kind":621,"options":622,"correct":631},"choice",[623,625,627,629],{"id":115,"label":624},"The hip has weaker muscles than the shoulder",{"id":118,"label":626},"The shoulder socket is shallow (freer); the hip socket is deep (more stable)",{"id":121,"label":628},"The hip is not really a ball-and-socket joint",{"id":124,"label":630},"The leg is simply too heavy to lift as high as an arm",[118],[633,634],"Think back to the girdle comparison in Understand: one girdle is built for reach, one for load.","A shallower socket allows more movement but is less stable; a deeper socket is the opposite.",{"correct":636,"incorrect":637},"Correct. Both joints share the same basic ball-and-socket design, but the socket depth is tuned to a different job: shallow and free at the shoulder, deep and stable at the hip.","Not quite. Both are ball-and-socket joints of the same basic type; the difference is entirely in how deep each socket is, which trades range of movement against stability.",{"id":639,"type":103,"title":640,"eyebrow":641,"navLabel":642},"i-ch-sizematch","How good is your sense of scale?","Chapter 08","8 Size-match challenge",{"id":644,"type":46,"markdown":645},"i-sizematch-intro","You have now measured real numbers for several organs and bones. The last test is a test of intuition: can you judge relative size correctly without a ruler, just by comparing one organ with an everyday object?",{"id":647,"type":82,"prompt":648,"options":649,"explanation":658},"i-predict-sizematch","Before playing the lab below, guess: is an adult brain closer in size to a tennis ball, a closed fist doubled in size (two fists), or a football?",[650,652,654,656],{"id":115,"label":651},"A tennis ball",{"id":118,"label":653},"About two fists held together",{"id":121,"label":655},"A full-size football",{"id":124,"label":657},"A grain of rice, scaled up in the imagination only","**About two fists held together**, at roughly 1.4 kg. A tennis ball is far too small and a football is too large. This is one of the most commonly misjudged sizes in the whole body — most people picture something bigger than the truth.",{"id":660,"type":233,"component":661,"componentVersion":5,"config":662,"objective":684,"textAlternative":685,"help":686},"i-lab-sizematch","body-explorer",{"views":663,"parts":666,"modes":682},[664,665],"organs","skeleton",[667,670,673,676,679],{"id":668,"note":669},"heart","About the size of your own closed fist, roughly 300 g — closer to a large potato than a football.",{"id":671,"note":672},"brain","About 1.4 kg, roughly the size of two fists held together — closer to a small cauliflower than a basketball.",{"id":674,"note":675},"liver","About 1.5 kg, roughly the size of a rugby ball — the largest internal organ, but still smaller than most people guess.",{"id":677,"note":678},"kidneys","Each about 11 cm, roughly the size of a bar of soap, not a dinner plate.",{"id":680,"note":681},"femur","In a 150 cm person, about 40.1 cm — close to the length of a school ruler and a bit more.",[683],"size-match","Match each organ or bone to the everyday object closest to its real size, before checking the true measurement.","The lab shows an outline body with five parts marked, and a shelf of everyday objects of different sizes below it: a grain of rice, a bar of soap, a fist, a large potato, a rugby ball, a football, a school ruler, a cauliflower.\n\nDrag the object you think is the closest size match onto each organ before revealing the true figure. Most learners overestimate the brain and the heart, expecting something closer to a football or a melon, and underestimate how much of the belly a fist-sized heart or two-fist brain really needs.",{"simplerExplanation":687,"hints":688},"Guess which everyday object is closest in size to each organ, then check the real measurement against your guess.",[689],"A closed fist is a genuinely good stand-in for a heart. Look at your own fist before you answer.",{"id":691,"type":233,"component":692,"componentVersion":5,"config":693,"objective":712,"textAlternative":713,"help":714},"i-lab-match-forensic","match-pairs",{"prompt":694,"mode":695,"pairs":696},"Match each measurement a scientist can take to what it helps them estimate.","connect",[697,700,703,706,709],{"a":698,"b":699},"Length of a femur","Approximate height of the person",{"a":701,"b":702},"Number of teeth present in a young child","Approximate age of that child",{"a":704,"b":705},"Whether growth plates have closed on an X-ray","Whether someone has finished growing taller",{"a":707,"b":708},"Arm span compared with height","Whether the Vitruvian rule fits this particular person",{"a":710,"b":711},"Resting pulse compared with pulse after exercise","How strongly the heart responded to activity","Connect five measurements to the estimate each one supports, tying every investigation in this layer together.","Five clue cards and five estimate cards, shuffled. Every pair in this game is drawn directly from an investigation earlier in the layer, so getting all five correct is a genuine check on whether the connections stuck, not just the numbers.",{"simplerExplanation":715},"Each measurement on the left is a clue. Match it to the question on the right that it actually helps answer.",{"id":717,"type":718,"conceptId":719,"relation":720,"explanation":721},"i-conn-data","connection","data-handling","applied_in","Every investigation in this layer produced a small real data set — heights, pulses, differences — and used mean, median, mode and range to describe what the class actually found.",{"id":723,"type":718,"conceptId":724,"relation":725,"explanation":726},"i-conn-body-systems","body-systems","related_to","A rising pulse after exercise is a body-systems story: how the heart, lungs and muscles hand work to each other. This layer only measures the effect; that topic explains the mechanism.",{"id":728,"type":103,"title":729,"eyebrow":730,"navLabel":731},"i-ch-close","Check yourself","Chapter 09","9 Check yourself",{"id":733,"type":734,"title":735,"questions":736},"i-quiz","quiz","Ten questions on what the tests actually showed",[737,750,763,776,789,802,815,828,840,853],{"itemId":738,"prompt":739,"options":740,"correct":118,"why":749},"human-body-anatomy.investigate-q-tube","Why did the rolled paper tube hold more books than the flat folded strip, using the same paper?",[741,743,745,747],{"id":115,"label":742},"Paper becomes stronger when it is rolled",{"id":118,"label":744},"The tube shape moves material away from the centre, which resists bending better",{"id":121,"label":746},"The tube weighs less",{"id":124,"label":748},"It was a coincidence; both should be equally strong","Same material, same mass, different shape. Moving material outward into a ring, away from the centre line, is what makes a shape resist bending well — the same reason your long bones are hollow tubes.",{"itemId":751,"prompt":752,"options":753,"correct":118,"why":762},"human-body-anatomy.investigate-q-span-average","In the class of 15, the mean height and mean arm span were very close, but every single pupil differed from their own height by some amount. What does this show?",[754,756,758,760],{"id":115,"label":755},"The rule is completely false",{"id":118,"label":757},"A rule can be true on average without being exact for any one individual",{"id":121,"label":759},"The measurements must have been taken wrong",{"id":124,"label":761},"Arm span is a more reliable measurement than height","Averages can hide real individual variation. The rule held well for the group and only approximately for each person in it — both statements are true at once.",{"itemId":764,"prompt":765,"options":766,"correct":118,"why":775},"human-body-anatomy.investigate-q-forensic-formula","Height ≈ femur ÷ 0.267. A femur measures 42.7 cm. What height does this predict?",[767,769,771,773],{"id":115,"label":768},"About 114 cm",{"id":118,"label":770},"About 160 cm",{"id":121,"label":772},"About 200 cm",{"id":124,"label":774},"About 42.7 cm","42.7 ÷ 0.267 ≈ 159.9 cm, so about 160 cm is the closest.",{"itemId":777,"prompt":778,"options":779,"correct":118,"why":788},"human-body-anatomy.investigate-q-forensic-limit","Why do real forensic scientists use several equations and give a range, rather than one single ratio like the one used in this layer?",[780,782,784,786],{"id":115,"label":781},"Because the femur is too hard to measure accurately",{"id":118,"label":783},"Because the true ratio differs slightly between sexes and populations",{"id":121,"label":785},"Because height cannot really be estimated from bone at all",{"id":124,"label":787},"Because computers cannot do the division accurately","A single average ratio is somewhat wrong for almost everyone. Careful science accounts for that by using several calibrated equations and stating a margin of error, rather than presenting one number as exact.",{"itemId":790,"prompt":791,"options":792,"correct":118,"why":801},"human-body-anatomy.investigate-q-pulse-direction","After mild exercise, what happened to every single pupil’s pulse in the class data?",[793,795,797,799],{"id":115,"label":794},"It fell for everyone",{"id":118,"label":796},"It rose for everyone, but by different amounts",{"id":121,"label":798},"It stayed exactly the same for everyone",{"id":124,"label":800},"It rose for exactly half the class","Direction was universal (every pulse rose) while size of the rise varied hugely, from 4 to 28 bpm.",{"itemId":803,"prompt":804,"options":805,"correct":118,"why":814},"human-body-anatomy.investigate-q-heart-response","Why does a pulse rise during exercise at all?",[806,808,810,812],{"id":115,"label":807},"The heart shrinks and beats faster to compensate",{"id":118,"label":809},"Working muscles need more oxygen-carrying blood delivered faster",{"id":121,"label":811},"The lungs stop working properly during exercise",{"id":124,"label":813},"It is a random, meaningless change","Cardiac muscle cannot instantly grow bigger, so the heart answers a higher demand for oxygen the only way it can in the moment: beating faster and a little harder.",{"itemId":816,"prompt":817,"options":818,"correct":118,"why":827},"human-body-anatomy.investigate-q-symmetry-hands","Careful measurement usually finds that a person’s left and right hand spans are:",[819,821,823,825],{"id":115,"label":820},"Exactly identical, always",{"id":118,"label":822},"Close, but almost never exactly equal",{"id":121,"label":824},"Wildly different",{"id":124,"label":826},"Impossible to measure consistently","Close under everyday inspection but rarely identical under a careful ruler — completely normal, and no cause for concern.",{"itemId":829,"prompt":830,"options":831,"correct":121,"why":839},"human-body-anatomy.investigate-q-symmetry-organs","Which of these is a genuinely, deliberately asymmetric feature of the body, not just a small measuring difference?",[832,834,836,837],{"id":115,"label":833},"Left vs right foot length",{"id":118,"label":835},"Left vs right hand span",{"id":121,"label":574},{"id":124,"label":838},"Left vs right eye-to-nose distance","2 lobes on the left against 3 on the right is a real, built-in asymmetry caused by the heart, not measurement noise.",{"itemId":841,"prompt":842,"options":843,"correct":118,"why":852},"human-body-anatomy.investigate-q-handspan","A 120 cm desk is measured by two pupils with different hand-span sizes. What is true?",[844,846,848,850],{"id":115,"label":845},"Both must report the same number of spans",{"id":118,"label":847},"The pupil with the smaller hand span reports a bigger number of spans",{"id":121,"label":849},"The pupil with the smaller hand span reports a smaller number of spans",{"id":124,"label":851},"Hand-span measuring is impossible with more than one person","A smaller hand span covers less of the desk each time, so more of them are needed to reach the end — a bigger number, for the exact same desk. This is exactly why standard units like the centimetre replaced body-based ones.",{"itemId":854,"prompt":855,"options":856,"correct":118,"why":865},"human-body-anatomy.investigate-q-scale","Roughly how big is a typical adult heart?",[857,859,861,863],{"id":115,"label":858},"The size of a grain of rice",{"id":118,"label":860},"The size of a closed fist",{"id":121,"label":862},"The size of a football",{"id":124,"label":864},"The size of a dinner plate","About 300 g and fist-sized — smaller than most people guess before measuring their own fist against the figures.",{"id":867,"type":423,"prompt":868},"i-reflect-close","Of the seven claims tested in this layer, which one matched your prediction least well? Write two sentences on what you expected, and two on what you actually found. Being specifically wrong once is worth more to memory than being vaguely right five times.",{"id":870,"type":871,"title":872,"points":873},"i-summary","summary","Cheat sheet",[874,875,876,877,878,879,880],"**Hollow beats solid.** For the same mass of material, a tube resists bending better than a rod — true for paper columns, bamboo scaffolding, bicycle frames and hollow long bones.","**Averages hide individuals.** Class mean height (148.9 cm) and mean arm span (149.0 cm) were very close, yet every pupil differed from the rule by some amount, up to 2 cm either way.","**Body-based units disagree; standard units do not.** The same 120 cm desk gave every pupil a different number of hand spans, from 5.5 to 7.5, because their hands differ in size. A centimetre never does that.","**Height from a bone.** Height ≈ femur ÷ 0.267. Useful and testable, but built from an average ratio — real forensic work uses several calibrated equations with a stated margin of error.","**Exercise always raises pulse, never by a fixed amount.** Class mean rise was 17.6 bpm after mild exercise, but individual rises ranged from 4 to 28 bpm.","**Roughly symmetric outside, deliberately lopsided inside.** Paired outward measurements (hands, feet, eye distances) are close but rarely exact. Single internal organs are either matched exactly in number (ribs) or asymmetric by design (heart, lungs, liver).","**A rule can be true on average and only approximately true for any one person — this is not a contradiction, and it is worth checking, every time, which kind of claim you are looking at.**",{"id":882,"type":883,"sourceIds":884},"i-sources","sources",[885,886,887,888,889],"human-body-anatomy-britannica-human-body","human-body-anatomy-britannica-skeleton","human-body-anatomy-britannica-muscle","human-body-anatomy-wikipedia-organ-list","human-body-anatomy-ncert-textbooks",[885,886,887,888,889],"needs_review",{"generatedBy":893,"notes":894},"claude-code","Draft generated locally; pending owner review. Every figure is computed and asserted in scratchpad\u002Fhuman-body-anatomy\u002Ffacts.py.","76802a05d5df430f0f36ba70f77f7f23a2daee94a4fab7de90d3b3b42c48a5de",{"component:data-lab@1":897,"logic:practice":898,"component:sort-game@1":899,"component:body-explorer@1":900,"component:match-pairs@1":901,"source:human-body-anatomy-britannica-human-body":902,"source:human-body-anatomy-britannica-muscle":903,"source:human-body-anatomy-britannica-skeleton":904,"source:human-body-anatomy-ncert-textbooks":905,"source:human-body-anatomy-wikipedia-organ-list":906},"466896cc37735f48db03875fe9c9ce42fc8bcb7e5f937c9779d70513703b91bd","3d6b0fe1b15255975a32b0fcd94e8019bc959ad45cbf12e136e86149549c6878","b164f45a2c8ca08f26c450768ff0231e113e9fe45381eddb34dc6d0548596c38","b44b6ef91c082fccbb2437932390f32c3cdec3d3b00c1261c62e6f7a421e644b","2a8ee4ac87460b4e1175a4bb13c96b03d577db06dde95670eb7fcfe4ad787899","d8eb8accac4fca64e6711169db72028b260fb8b81c937c86516d9009896fa34c","b2397d7be01ef8cf5211da5eca1573ad62d46085f36d4db2ed08f21c53056557","193bc0eb450e6145811c970ee092582c5438e4c1a9b77f43068da210057b43d4","efd8ff1189b2fa80028f5c70765a1028db96825546b54365d07ce2b79ce43928","6ae52bf16d9cf93ff90c426eeb0f7cb7f36e504d5e893cbcecd97a44a5fb6c9e",{"state":908,"reviewer":909,"selfReview":910,"reviewedAt":911,"method":912},"approved","The library owner",true,"2026-09-20T10:18:37.581Z","owner_bulk","preview-7e1cbbcc4f",1789899598709]