forces

Work is donewhen an objectis movedover a distanceby a forceappliedin thedirectionof its displacement

work done (joules) = force (Newtons) * distance (m)

1 Joule = 1 Newton metre

Ifa forceacts in thedirection that an objectis moving,then theobjectwillgain energy Iftheforceacts in theoppositedirection tothemovementthen theobjectwill loseenergy

mechancially

When friction is present, energy is transferredby heating This raises thetemperature(energy is transferredtothethermal store) oftheobject andits surroundings Theworkdoneagainstthefrictionalforces causes this risein thetemperature

Imperfections attheinterfacebetween theobject andthesurfacebumpintoandrubup againsteach other Notonlydoes this slow theobjectdown but alsocauses a transferofenergy tothe thermal storeoftheobject andthesurroundings

Particles bumpintotheobject as itmoves through theair As a result, energy is transferredby heatingduetotheworkdoneagainstthefrictional forces

For stationaryobjects, morethan oneforcehas tobeappliedtochangetheir shape

Their shapecan changeby: Stretching(forces in oppositedirections away from theobject) Bending(forces thatdistorttheobject) Compressing(forces in oppositedirections towards theobject)

An exampleofcompression is placinga mass on topofa springplacedon a flat surface Thetwoforces are: Theweightofthemass Thereaction forcefrom thesurfacetothespring the 2 forces are towards each other

An exampleof stretchingis placinga mass on thebottom ofa vertically hangingspring Thetwoforces are: Theweightofthemass Thetension in thespring forces are away from each othr

An exampleofbendingis a divingboardbendingwhen a swimmer stands atthefarend Thetwoforces are: Theweightoftheswimmer Thereaction forcefrom theblock tothedividingboard forces act towards each other, but at different points on obj. bending can alos be cuased by two forces at angle to each other

Achangeof shapeis calleda deformation andcan eitherbe: Elastic Inelastic

Whenobjects return totheiroriginal shapewhen thestretchingforceis removed Examples ofmaterials that undergoelasticdeformation are: Rubberbands Fabrics Steel springs

Whenobjects remain stretched and donot return completely totheiroriginal shape even when thestretchingforceis removed Examples ofmaterials that undergoinelasticdeformation are: Plastic Clay Glass

Therelationshipbetween theextension ofan elasticobject andtheappliedforceis defined by Hooke’s Law Hooke’s Law states that: Theextensionof an elasticobject is directlyproportional totheforceapplied, up tothelimit of proportionality

Thelimit of proportionality is whereifmoreforceis added,theobjectmay extendbutwill not return toits original shapewhen theforceis removed(itwillbeinelasticallydeformed) This varies accordingtothematerial

f = k * e Where: F =forcein newtons (N) k=springconstantin newtons permetres (N/m) e =extension in metres (m)

how stif a spring is higher the spring const, higher the stiffness

Hooke’s law is thelinearrelationshipbetween forceandextension This is representedby a straight lineon a force-extension graph materials not obeying this have non inear relationship - represenyed by curve on graph Any materialbeyondits limitofproportionality will havea non-linearrelationshipbetween forceandextension

Iftheforceis on they axis andtheextension on thex axis,thespringconstantis the gradient ofthestraight line(Hooke’s law) region ofthegraph Iftheforceis on thex axis andtheextension on they axis,thespringconstantis 1 ÷gradient ofthestraight line(Hooke’s law) region ofthegraph

Theenergy stored in an elasticobject when work is doneon theobject Providedthespringis notinelasticallydeformed(i.ehas notexceededits limitof proportionality),theworkdoneon thespringandits elasticpotentialenergy storedare equal

1/2 k e^2 Where: E =elasticpotentialenergy in joules (J) k=springconstantin newtons permetre(N/m) e =extension in metres (m)