COM M UNITY SCIENCE JOURNAL

Vol. 4 No. 1M ay 2007

Also:

CSCA tak e s part in Science World

Th e H istory of Nuclear W eapons

Toxic H eavy M etals

Th e O fficial Journal of th e Com m unity Science Centre As sociation

Robotics w ith Aras h M arzi

CSJ M ay 2007 - 2

PUBLISH ER Antonio W e ingarts h ofer, D. Sc.w e ingarts h ofer@ ns .sym patico.caEDITOR Cath erine H ollow aycath erine .h ollow ay@ dal.caPRODUCTION George vanAudenh ove, B. Eng.vanauden@ dal.caYOUTH CO -O RDINATOR Adam W h alenCH AIR Andrew M acDougallx2004apm @ stfx.ca

Affiliated O rganizationsiDLabTh e Sch ool of Education, St. Francis Xavier Univers ityTh e Discovery CentreTh e Antigonis h Regional Developm ent Auth ority

Supporting O rganizationsTow n of Antigonis hRegional Sch ool Advisory CouncilAntigonis h Guysborough Black Developm ent As sociationAntigonis h Detach m ent of th e RCM P

Th e Com m unity Science Journal is publis h ed m onth ly by th e Com m unity Science Centre As sociation, a registered non-profit organization. For over ten years , th e CSCA h as be en h elping youth learn about science , th rough m entoring and h ands -on experim entation. Th e CSJ is intended as a forum in w h ich youth , teach ers , and persons intere sted in science education can s h are th e ir opinions and ideas . All content is th e property of its re spective auth or(s) and/or th e CSCA.

Com m ents , sugge stions and e s says are invited. Inq uirie s s h ould be directed to cscaorg@ gm ail.com or to Th e Com m unity Science Centre As sociation, c/o Antonio W e ingarts h ofer, Ph ys ics Dept., P.O . Box 5000, Antigonis h , Nova Scotia, Canada, B2G 2W 5.

Th e deadline for contributions to th e next is sue is June 24th , 2007.

CSJM ay 2007 - Vol. 4 No. 1

Table of Conte nts

Editorial 3CSC Lecture Serie s 3CSC Participate s in M ayfe st 4CSC M em ber W ins at Science Fair 5

Fe ature sH istory of Science : Th e M anh attan ProjectM ark W illiam s 6Water, th e Strange st Substance Know n to ScienceAdam W h ale n, Le iff and De von Watson 7Th e Ins ect BirdCath e rine H ollow ay 9

Stude nt Re se archDeterm ining w h eth e r contextual or cued stim uli are m ore effective at triggering a fear-bas ed re spons e in m iceJoyce W . Y. Yu 10Predisposal to Drug AddictionKate lyn Ch e rw onick 13Analyzing Th e Interactions O f Biologically Relevant M olecules W ith Bism uth And W ith LeadPaul N. Duch e sne , Je nnie K . Le e , Sunis h a Ne upane 16

Re se arch ProfileDr. Sh ilpi M ajum de r, Psych ology 20

CSJ M ay 2007 - 3

Editorial

W h en I joined th e com m unity science centre th re e years ago, it w asn’t becaus e I saw it as a force to ch ange th e w orld or bring th e tow n togeth e r. I didn’t even expect to learn anyth ing about science . I joined becaus e it w as a place to talk about science w ith oth er people of s im ilar intere sts . Becaus e it w as th e clos e st th ing to a science club th at Antigonis h h ad to offer, som eth ing th at th e h igh sch ool didn’t.

Th e science centre h as an im portant role to play in our com m unity. Even if it doe s not produce scientists , it w ill h elp to m ak e adult citizens w ith an intere st in and

re spect for science . Citizens w h o w ill be outraged w h en science is censored or ignored for political or com m ercial reasons , and w ith th e savy to navigate out increas ingly tech nological w orld w ith out falling prey to q uak ery.

W e h ave lofty goals and lim ited re source s , tw o th ings th at do not go togeth e r w ell. But w e don’t ne ed to ch ange th e w orld. All w e ne ed to do is k e ep th e Science Centre open and w ork ing as be st it can, so th at students can h ave th e sam e experience as I did th rough th e years to com e, w h eth e r our num bers be tw o or tw o h undred. W e s h ould never undere stim ate th e value of a place th at advocate s science as fun.

Cath e rine H ollow ay

Th e W edne sday afternoon lecture s e rie s is an after sch ool program be ing run th is spring by th e com m unity science centre as sociation. Th e objective of th e s e rie s is to bring th e com m unity and Univers ity togeth e r in order to educate th e public about th e natural science s and m ath em atics , discipline s on w h ich our civilization is dependant but about w h ich m ost people are unfam iliar. Th e s e rie s is prim arily aim ed at H igh Sch ool students , but is open to all age s , w ith th e obs e rved age range of audience m em bers from 8 to 81.

As of th e tim e of w riting, th e re h ave be en ten lecture s . Topics h ave be en divers e and h ave included; ‘Life th e Univers e and Everyth ing’, ‘H ow and W h y Plants and Anim als get th e ir Colours’, ‘Th e us e of Biotelem etry and GIS in Fis h e rie s Biology’, ‘Clim ate Ch ange and Infectious Dis eas e s’, and ‘Fractals th e CN Tow er and Pine Cone s’. Th e M ost recent of w h ich , ‘Brain calculations : H ow th e cerebellum controls coordination’ a lecture pre s ented by Dr. Angela Brack enbury, included th e exh ibition of real s h e ep brains and a dem onstration, w ith crystal glas s e s ,

about h ow th e cerebellum com pensate s for corrupted input from th e s ens e s .

Th e Com m unity Science Centre cons iders th is year’s lecture s e rie s a h uge succe s s and plans to continue th e lecture s e rie s in th e fall of 2007. W ith luck th e CSCA h ope s to continue th e s e rie s perpetually into th e future as one of our core activitie s .

Com m unity Scie nce Ce ntre Le cture Se rie s: Bringing Scie nce to th e PublicAndrew MacDougall

Dr. Angela Brack enbury h olds a m odel of a h um an brain

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M ayfe st is a Sure Sign of Spring.

Th e true s ign th at Spring is h e re com e s w ith th e excitem ent of M ayfe st w h ich is th e annual fundrais e r of St. M arth a's H ospital Auxillary. All s ectors of th e com m unity bring th e ir be st attractions and h om e bak ed pastrie s to th e Bloom field Centre to deligh t, to entertain and to inform th e local population. Young ch ildren h ave a ball.

Th e Science World is a popular attraction, put togeth e r w ith booth s from th e science departm ents at St. FX. It's a golden opportunity to s h ow th at doing science and learning h ow nature w ork s is fun. Th e Com m unity Science Centre

As sociation prepared a h ands -on exh ibit on w ater, th is unk now n liq uid th at w e s im ply tak e for granted. After interacting w ith th e youngsters and th e ir parents , w e believe th at w ater is inde ed a w onderful topic to bring science alive .

At th e display w e h ad tw o Grade 6 students , Leiff and Devon Watson, s h ow ing th e youngsters th at m olecules com e in all s h ape s and th at w ater is a bend m olecule. Th e youngsters w ere exploring th e s h ape s by us ing gum drops and tooth pick s .

Adam W h alen, an am ateur prospector, w as dem onstrating th e ph ys ics and th e art of panning for gold w h ile h e w as telling storie s about th e M ining M us eum in Goldenville.

For m ore inform ation about th e dem onstrations pre sented at Mayfe st, please se e page 7.

Com m unity Scie nce Ce ntre Participate s in Mayfe stDr. A. W e ingartsh ofe r

George VanAudenh ove , Le iff and Devon W atson ope rate th e CSC booth at Science W orld

Adam W h alen dem onstrate s gold panning

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Com m unity Scie nce Ce ntre Me m be r w ins at Canada W ide Scie nce FairDr. A. W e ingartsh ofe r

Aras h M arzi's "Controllable Autom otive Robot" (C.A.R.) reach ed th e national level of th e Canada W ide Science Fair Com petition. Som e 500 students from acros s Canada converged on Truro, Nova Scotia to experience a w e e k of friendly rivalry and great fellow s h ip. Aras h is a student at th e junior h igh sch ool in Antigonis h and h as be en com ing to th e science centre for four years .

H e w as th e Silver M edalist in h is category, Com puting and Inform ation Tech nology. Th e As sociation of Profe s s ional Engine ers of Nova Scotia declared h is C.A.R. th e "be st engine ering entry". Along w ith th e s ilver m edal from th e Strait Regional Science Fair, h e also w on anoth er from th e Youth Science Foundation of Canada. H e w on m oney in th e bank for th e future : a $1500 entrance sch olars h ip from th e Univers ity of W e stern O ntario. Th e h onorary certificate s th at h e rece ived could cover a w h ole w all in h is h ous e .

Th e w e e k -long gath ering put a lot of em ph as is on displaying th e oth er talents of th e candidate s , dem onstrating th at budding scientists are w ell rounded individuals . Aras h did not bring h is violin but h e h ad h is tae k w ondo gear and dem onstrated th e art of break ing tw o and th re e solid w ooden boards w ith one tactical m ove w ith h is bare fe et.

Aras h m ade m any new friends and th e Youth Science Foundation of Canada (YSF) nom inated h im to th e m em bers h ip of Student M entors h ip As sociation Regarding Tech nology and Science (SM ARTS). SM ARTS is th e YSF's for youth , by youth netw ork th at connects young Canadians w ith science - and one anoth er.

Th e em ph as is in SM ARTS is 'M entors h ip'. Aras h fe els th at if h e could reach th e top, so can oth er youngsters . O f cours e , it is h ard w ork and deditcation, along w ith guidance, th at w ill get th em th e re . H e is prepared to h elp h is fellow students get into com puting and inform ation tech nology and build robots . It's fun and offers a m ultitude of practical applications . Aras h is offering h is h elp to anyone w h o w ould lik e it. So, let's form a robotics club in our com m unity!

Aras h 's fam ily s h are s a good part of th is succe s s story. H is fath er, Dr. H osain M arzi, a profe s sor at St. FX, offered h is tech nical guidance . H is m oth er M inoo and older s ister Elh am h ave be en very supportive .

Aras h is cons idering offering pre s entations w ith practical dem onstrations . Th e s e w ill be sponsored by th e Com m unity Science Centre As sociation, of w h ich Aras h h as be en a m em ber s ince grade four.

Dr. Mich ael Ste initz capture s a spark on th e Van de r Graaff Gene rator at Science W orld

CSJ M ay 2007 - 6

August 19 45: th e US drops nuclear w eapons in air raids on H iros h im a and Nagasak i, w h ich led to th e capitulation of Japan in th e dying days of th e w ar. It w as th e first and only us e of a tech nology th at w as earth -s h attering, in m ore th an one s ens e of th e w ord.

Th e notion of us ing som e form of nuclear pow er e ith e r for energy or m ilitary applications h ad actually be en around for s everal years prior to th e beginning of th e w ar. Radioactivity in uranium w as discovered in 189 6 by H enri Becq uerel, a French ph ys icist, and scientists h ad be en studying it s ince to s e e if it could be h arne s s ed for th e production of energy. Unfortunately, th ings didn’t exactly progre s s at a spe edy pace; even by th e 30’s , th e us e of nuclear energy w as m ore of a dream th an a reality. In th eory, it w as entirely pos s ible; th e problem w as figuring out h ow to safely and efficiently obtain it.

Still, re s earch did progre s s and m ore k now ledge w as accum ulated. Th e real catalyst for developm ent in th e field of nuclear energy, h ow ever, w as th e beginning of H itler’s Th ird Re ich . After be ing elected Ch ancellor in 19 33, and th en appointed h ead of state in 19 34 follow ing th e death of Pre s ident Paul von H indenburg, H itler proce eded to carry out h is notorious policie s . H is pers ecution of th e Jew is h people w as greatly intens ified, caus ing m any Jew is h -Germ an scientists to flee th e country and h ead to th e US. H e also w ork ed h ard to revitalize th e Germ an m ilitary, in direct violation of th e Treaty of Versailles . Th is , com bined w ith H itler’s gradual extens ion of pow er in Europe (ie , th e annexation of Austria in 19 38, th e annexation/invas ion of Czech oslovak ia in 19 38-39 ) alarm ed m any of th e aforem entioned scientists w h o fled th e nation. Th ey k new th at Germ any w as conducting re s earch on th e pos s ibility of h arne s s ing nuclear pow er, and th ey feared th at th is w as to be done for furth er m ilitary purpos e s .

In order to prevent H itler from developing th is capability (or at th e very least, beat h im to it), s everal of th e s e scientists w ork ed togeth e r in an effort to get Frank lin Delano Roos evelt, th e US Pre s ident at th e tim e , to develop an Am erican nuclear program . Th ey h ad little succe s s in getting th e attention of Was h ington until Albert Einste in, a th eoretical ph ys icist and h im s elf a Jew is h -Germ an refugee , decided to lend h is support to th e caus e . Roos evelt th en took intere st in th e caus e , due in part to Einste in’s fam e and

reputation, and also due to th e fact th at Poland h ad just recently be en invaded by th e tim e h e h ad rece ived contact from Einste in and th e oth ers . Funding w as approved, and a com m itte e e stablis h ed.

At first, progre s s w as q uite slow ; th e US w as not yet involved in th e w ar w h en th e project w as begun (th e US didn’t join th e effort until 8 Decem ber 19 41). O nce w ar w as declared, h ow ever, re s earch progre s s ed sw iftly. Now confronted w ith th e pos s ibility of an attack on its ow n soil, th e US w anted to ensure th at it w ould h ave th e upper h and m ilitarily. Robert O ppenh e im er, an Am erican th eoretical ph ys icist from th e Univers ity of California, Berk ley, joined

th e project in 19 42. Th e effort continued to expand, and soon included not only scientists from th e US and refugee s from Germ any, but follow ing th e Quebec Agre em ent of 19 43, Britis h and Canadian re s earch e rs . Th e project w as w ell on its w ay.

Finally, in 19 45, after years of re s earch , th e M anh attan Project h ad developed tw o w ork ing vers ions of a nuclear w eapon (now w e get to th e fun stuff!). Th ough it took years of h ard w ork and billions of dollars , th e final de s igns w ere surpris ingly s im ple. Th e first bom b to be us ed in a m ilitary scenario, a uranium bom b nick nam ed “Little Boy”, w as e s s entially a tube w ith uranium -235 at each end, and an explos ive ch arge

at th e front. W h en th e bom b h ad reach ed a suitable h e igh t in its de scent over H iros h im a, th e explos ive ch arge at th e front w as s et off. Th is caus ed th e uranium at th e front of th e bom b to be “ s h ot” to th e oth er end of th e bom b, and collide w ith th e oth er m as s of uranium . Th e force w ith w h ich th e tw o m as s e s collided, com bined w ith th e confined space in th e bom b, caus ed th e uranium to reach critical m as s and detonate . I realize th at th is is not th e m ost detailed explanation, but th en, th e de s ign really isn’t th at com plicated. Plus, I’m an arts student . . . let’s k e ep our expectations realistic.

Th e s econd bom b, th e one us ed at Nagasak i, w as a plutonium bom b nick nam ed “Fat M an” (ok , so th e w eren’t very creative). W h ile plutonium w as q uite h ard to obtain and h ad only be en discovered in 19 41, th e de s ign of th e plutonium bom b also proved to be rath er s im ple. A sph e rical m as s of plutonium w as placed in th e centre of th e bom b, w ith explos ive ch arge s placed around it. As w ith th e first one , th e ch arge s w ere th en s im ultaneously detonated w h en

H istory of Scie nce : Th e Manh attan Proje ctMark W illiam s

CSJ M ay 2007 - 7

th e bom b h ad reach ed its proper h e igh t over Nagasak i. Th e s e ch arge s , spaced and tim ed precis ely to ensure th at force w as applied e q ually to th e entire surface of th e plutonium sph e re , forced th e plutonium to contract and im plode . Th e plutonium th en reach ed critical m as s and, bada-bing bada-boom . . . w ell, boom .

P.S. For th os e of you w ondering: it w as called th e M anh attan Project becaus e it w as originally h eadq uartered in

M anh attan. Th e m ajority of th e re s earch and te sting, h ow ever, w as conducted at various scattered s ite s acros s th e US.

M ark W illiam s is a H istory M ajor at St. FX Unive rs ity

A rath er odd th ing to say about a substance as fam iliar as w ater, but it is surely true . Just th ink of tw o propertie s th at are uniq ue to w ater. Ice floats on w ater and our m arine life is protected becaus e of it. In th e w inter w ater com e s dow n as snow and not as ice pellets if it w ere an ordinary substance .

Com pared to oth er ch em ical substance s (containing h ydrogen atom s , lik e am m onia) w e find th at its m elting point and boiling point are very m uch h igh e r. If th is w eren't so liq uid w ater w ould be scarce on Earth and biological m ach inery involving DNA and prote ins w ould h alt. Water's h eat of vaporization is very h igh , so th at th e w ater th at w e spread on fore st fire s tak e s a lot of h eat out of th e fire th e reby allow ing q uench ing and cooling dow n th e fire .

All th e s e life -giving propertie s of w ater ow e th e ir existence to a uniq ue k ind of ch em ical bond called a 'h ydrogen bond' w h ich still rem ains m ysterious de spite intens e scrutiny. Th e tw o strands in th e double h elix structure of DNA are bonded by h ydrogen bonds w h ich are strong enough to h old th em togeth e r and yet also w eak to operate lik e a 'zipper' for DNA to carry out its vital functions .

In sum m ary, w e w is h to stre s s th at life ow e s its existence to th is relatively w eak bond w h ich joins m olecules . M uch science can be learned by exam ining w ater.

M olecules are aggregate s of atom s th at h ave a s h ape . Th ey can be linear lik e carbon dioxide or bent lik e w ater. Ke ep alw ays in m ind th at atom s h ave a negative cloud of m obile electrons sw irling around a m as s ive nucleus com pos ed of pos itive protons and neutral neutrons . Th e pos itive nucleus is 1836 tim e s m ore m as s ive th an th e m obile electrons . Th is fundam ental constant stabilize s th e structure of th e m olecules . Th e binding glue is determ ined by a s h aring proce s s of th e m obile electrons . Th is type of bond is called covalent and is th e stronge st ch em ical bond.

Diam onds are lik e big m olecules w h e re th e carbon atom s occupy th e vertice s of a tetrah ydron, w h ich com bined w ith th e covalent bonding betw e en th e carbon atom s is an illustration of th e stronge st ch em ical bond m ak ing diam onds th e h arde st k now n substance s . Sodium Ch loride is an exam ple of ionic bonding th at is som ew h at w eak e r of 'electrostatic attraction' in nature . Th en w e h ave 'm etallic bonding' lik e in copper, s ilver or gold w h ich is ch aracteristic of a lattice of pos itive m etal ions and a cloud of electrons th at m oves betw e en th e ions . Th ere are as m any fre e electrons as th e re are atom s in th e sam ple. Th is give s m etals th e ir ch aracteristic electrical propertie s and also m ak e s th em good m irrors . Th is is th e ligh t interaction w ith fre e electrons .

Th e m etallic bonding depends on th e pre s ence of fre e 'm obile' electrons . H ow ever, th e ir arrangem ent give s ris e to bonding strength s th at vary greatly from one m etal to anoth er. Th is m odel explains w h y gold and s ilver are so m alleable. Inde ed, th e noble m etal gold is so m alleable th at a craftsm an can h am m er an ounce of gold into a 300-s q uare foot s h e et. But w h y, ch em ists w onder, doe s gold rem ain tarnis h -fre e? H ow doe s it m anage to re s ist corros ion? Th e uniq ue role th at gold plays in society is due to th e fact th at it is th e m ost noble: th at m eans 'unreactive'. H ow ever, it doe s form

W ate r, th e Strange st Substance Know n to Scie nceAdam W h alen and Le iff and Devon W atson, w ith h elp from Dr. A W e ingartsh ofe r

CSJ M ay 2007 - 8

stable alloys w ith m ercury for instance . Th e s e are som e uniq ue surface propertie s th at h ave enabled scientists to study surface bonds of m etals th at play a m ajor role as catalysts in th e ch em ical industry and in m icroelectronics .

A popular dem onstration for th e youngsters w as th e ph ys ics of gold panning w h ich re q uire s great s k ill and is alm ost an art. Th e M ining M us eum in Goldenville, w h ich is a couple of k ilom eters from Sh erbrook Village, w as discus s ed in th e pre s entation.

In ice w e h ave a netw ork of h ydrogen bonds w h ich are som e 25 tim e s w eak e r th an covalent bonds but th e structure h as an open tetrah edron ch aracter w h ich m ak e s ice ligh ter th an liq uid w ater. O f im portance is th at som e of th is h ydrogen bonding pers ists in w ater and even in th e vapour ph as e th at give s w ater its peculiar propertie s of h aving h igh value s for its m elting and boiling tem perature s .

A very popular h ands -on activity -th at w e provided - w as m ak ing m olecules of various s h ape s w ith coloured gum drops and tooth pick s to em ph as ize th at m olecules h ave s h ape s . W e q uick ly ran out of gum drops unfortunately but w e h ad oth er h ands -on activitie s w ith w ater.

Water is a w onderful m edium to play w ith and do som e intere sting h ands -on ph ys ics to practice som e fundam ental tech niq ue s to m easure ph ys ical propertie s lik e surface tens ion and viscos ity.

(1) M easuring 'surface tens ion” w ith a spring

balance .

Surface tens ion determ ine s th e 'w etting propertie s ' of w ater. Th is fam iliar effect can be dem onstrated w ith a s et of capillary tube s of various bore cros s s ections . Th e concave m eniscus is a clear indication th at th e w ater clings to th e glas s . Capillarity effects explain th e com plex system of w ater transportation in plants and tre e s w h e re th e w ater can ris e to m ore th an 200 fe et from th e ground. Closely connected w ith th is is a stunning dem onstration of so-called coh e s ion plate s . Tw o polis h ed glas s plate s can strongly stick togeth e r w ith a film of w ater betw e en th em .

(2) M easuring viscos ity w ith th e h elp of Stok e 's law and dropping sm all sph e re s in a tall cylinder

filled w ith w ater and determ ining th e 'term inal velocity' as th ey fall th rough th e w ater. Th e term inal velocity is determ ined by th e viscos ity (to be m easured) and th e radius of th e sph e re s and th e ir dens ity.

(3) O f cours e , Arch im ede s ' ‘Eure k a’ exploit of h ow to determ ine dens itie s of irregular objects lik e th e 'crow n of a k ing'. Th e h ands -on dem onstration in th e Figure illustrate s th e procedure .

Leiff and Devon W atson are grade six students at SAJS

CSJ M ay 2007 - 9

Th e Inse ct BirdCath e rine H ollow ay

W h en th e first Europeans cam e to North Am erica, back in th e fifte enth century, m any w onders aw aited th em . A w h ole continent full of uniq ue societie s of m an and specie s of w ildlife, and am ong th em a creature so h ard to de scribe : th e h um m ingbird. Explorers w ere at a los s for w ords w h en trying to explain th e tiny creature : a bird w ith jew el-lik e ruby, em erald, black and w h ite feath ers , but lik e an ins ect, able to fly back w ards , h over, and drink nectar from flow ers . Astonis h ed, th ey reported it as just th at: th ey as sum ed th e h um m ingbird m ust be a m ix of both ins ect and bird.

Today, w e still m arvel at h um m ingbirds . From Canada to Brazil, from California to Nova Scotia, h um m ingbirds are a uniq uely Am erican feature . M any of us h ave built fe eders to attract th em , including m y grandfath er. H e live s in O h io and for m any years h e h as be en trying to attract h um m ingbirds to a fe eder near h is h ous e . Every sum m er, w h en I vis it, h e’s got th e brigh t red and yellow fe eder out in h is yard, and if anyone in th e h ous e h appens to s e e a h um m ingbird at th e fe eder, w e’re suppos ed to yell “H um m er Alert!” so th at h e can get a glim ps e of h is favourite bird.

Th is intere st is s h ared by Douglas Warrick , Bret Tobals k e , & Donald Pow ers , th re e biologists w h o k now a lot about aerodynam ics . Th ey w ere curious about h um m ingbirds , too. In particular, h ow m uch alik e are h um m ingbirds and ins ects w h en h overing? To satisfy th e ir curios ity, th ey de s igned and ran an experim ent involving olive oil droplets , las ers , an idle w ind tunnel, and of cours e , h um m ingbirds , w h o h ad to be specially trained for th e purpos e s of th e experim ent. Th e rufous h um m ingbirds , Selasph orus rufus , h over at a fe eder in th e air tunnel filled w ith olive oil vapour, generated at a rate of 7*10^10 particles per m inute . Th e vapour is pus h ed and pulled around by th e w ing strok e s of th e h overing h um m er, w h ile a las er illum inate s a cros s -s ection of th e w ak e . Th e droplets’ velocitie s can th en be m easured us ing a s ensor.

Watch ing a video of a h overing h um m ingbird from th e s ide s h ow s th at th e ir w ings follow a type of figure -e igh t, forcing air dow n in both strok e directions . To understand w h y th ey do th is , im agine yours elf treading w ater in a

sw im m ing pool. In order to k e ep your ears above th e w ater, you m ust continuously pus h w ater dow n, to pus h yours elf up. H ow ever, if you pus h straigh t dow n and up, you w ill loos e all th e w ork you h ave done pus h ing yours elf up w h en you rais e your arm s to repeat th e action. So, th e m ost effective strok e is a figure -e igh t, one w h ich m ak e s th e m ost of pus h ing dow n, w idth -w is e , and m ak e s th e least of th e upw ards m ovem ent, along th e edge s of th e figure . H um m ingbird w ings can rotate 180 degre e s in order to m ak e th is figure , a rare ability in th e avian w orld.

W h ich leads to th e re sults of th e biologists’ experim ent in aerodynam ics . Both ins ects and h um m ingbirds us e figure -e igh ts to h over, but unlik e ins ects , th e h um m er’s

bird bodie s prevents th em from sym m etrical h overing. In sym m etrical h overing, h alf of th e w e igh t of th e ins ect’s body is supported on th e dow n strok e and h alf on th e upstrok e . Contrast th is w ith your typical bird, w h os e w e igh t is supported com pletely on th e dow n strok e . Th e h um m ingbird is a m ix of both . Th e experim ent s h ow ed th at th e h um m ingbird supports 75% of its w e igh t on th e dow n strok e and 25% on th e upstrok e . Part bird, part ins ect.Now , th e really intere sting part is

th at a specie s of bird and a specie s of ins ect, th e Sph inx M oth , h ave both evolved in a w ay to us e th e sam e source of energy, flow er nectar, w ith th e sam e relative s ize and w ing strok e . Th e h um m ingbird h as evolved to split its m as s betw e en th e tw o strok e s lik e an ins ect becaus e it is th e m ost

efficient w ay of h overing, saving precious energy it ne eds to sustain w ing beat fre q uencie s as h igh as 75 tim e s per s econd and to k e ep its h eart beating at 1260 beats per m inute . H ow ever, h um m ingbirds are not com pletely efficient becaus e th e ir bird w ings and m uscles lim it th em .

Alth ough w e now k now th at h um m ingbirds are birds , not ins ects , th is experim ent just goe s to s h ow th at perh aps th os e early explorers w eren’t too far off.

For really neat slow videos of h um m ingbirds and sph inx m oth s , vis it w w w .w ildlifeth eatre .com

Cath e rine H ollow ay is a Ph ysics m ajor at Dalh ousie and th e editor of th e CSJ.