Physics 1st Semester Review
Whatareforces?
Aforceisapushorpullexertedbyoneobjectonanotherobject
Forcesarevectors;theyhavemagnitudeanddirection
Thesymbolforforceis“F”
TheSIunitforforceisaNewton(N)
Contactvs.Non-contactForces
Therearetwocategoriesthatforcesareclassifiedas:contactandnon-contact
Withcontactforces,theobjectsaretouchingintheinteraction
Withnon-contactforces,theobjectsdonottouchintheinteraction
ContactForces
Appliedforce-forceappliedonanobjectbyapersonoranotherobject
Frictionforce-forceexertedbyasurfaceasanobjectslides(orattemptstoslide)acrossit
Airresistanceforce-specialtypeoffriction
Normalforce-thereactionforceonanobjectfromthesurfaceitisrestingon
Springforce-forceexertedbyastretchedorcompressedspring
Tensionforce-transmittedthroughastring,rope,cableorwirewhenitispulledtightbyforcesactingfromoppositeends
Non-ContactForces
Gravitationalforce-forceofattractionbetweenbodiesofmass
Electricalforce-duetoelectriccharges
Magneticforce-duetomagneticdipoles
FundamentalForces
Therearefourfundamentalforces:
StrongNuclearForce:Holdsnucleustogether,strongestofthefundamentalforces
ElectromagneticForce:Betweenelectricallychargedparticles,secondstrongestfundamentalforce
WeakNuclearForce:Causesnucleardecay,secondweakestfundamentalforce
Gravity:Betweenbodiesofmass,weakestfundamentalforce
Allcontactandnon-contactforcesarisefromthefourfundamentalforces.
What’sinafree-bodydiagram?
Afreebodyisonethatisstandingalone;therefore,onlydrawtheobjectyouareanalyzinginthediagram.
Representtheobject(body)asabox,nomatterwhatitactuallyis
Onlydrawtheforcesactingontheobject,donotincludeforcestheobjectexertsonotherobjects
ForceisaVector
Forcescanberepresentedasarrows
Thelengthofthearrowrepresentsthemagnitude(size)oftheforce
Thedirectionofthearrowrepresentsthedirectionoftheforce
Drawthetailoftheforcecomingoutofthemiddleoftheobject
LabelingtheForce
Afterdrawingtheforcesinthediagram,labeleachone
Usethesymbol“F”forforce,andaddasubscriptdescribingthetypeofforce
Example:ForanappliedforceuseFapp
Example
NetForce
Thevectorsumofforcesactingonanobjectisthenetforce
Netforce=0
26400N
26400N
6400N
Manyorangutansspendtheirentirelivesamongthetreesandarewelladaptedtomoveinthisarborealhabitat.Theyhavelongarms(abouttwo-thirdsoftheirbodyheight)andpowerfulchestmuscles.Supposeanadultorangutanishangingbyitsarmsfromatreebranch.Theanglebetweeneachoftheanimal’sarmsandtheverticalis15°witheacharmexertingaforce430N.Thegravitationalforceactingonitis830N.Drawafree-bodydiagramoftheanimal.
Farm=430N
Farm=430N
Fgravity=830N
Θ=30o
Newton’s1stLawofMotion
Anobjectatrestremainsatrest,andanobjectinmotioncontinuesinmotionwithconstantvelocityunlesstheobjectexperiencesanetexternalforce.
ForceandAcceleration
Forcescancauseaccelerations(speedingup,slowingdown,changingdirection)
Ifthenetforceonanobjectisnotzero,theobjectwillaccelerate
Ifthenetforceonanobjectiszero,theobjectwillnotaccelerate
Inertia
Newton’s1stLawisalsocalledtheLawofInertia
Inertiaisthetendencyofanobjecttoresistchangesinitsmotion
Massisameasureofinertia.Themoremassanobjecthas,themoreinertiaithas.
Newton’sSecondLawofMotion
Ifanetforceisappliedtoanobject,thiscausesittoaccelerate.Theaccelerationisdirectlyproportionaltotheforce,andinverselyproportionaltothemass.
Force=massxacceleration
F=ma
Units
Force:Newtons
Mass:kilograms
Acceleration:m/s2
BecausemassandaccelerationaremultipliedinF=ma,wewouldexpecttheunitsforforcetobekgm/s2.ANewtonisequivalenttoakgm/s2.
Newton’sThirdLaw
Allforcesoccurinpairs,andthesetwoforcesareequalinmagnitudeandoppositeindirection.
Thisiscommonlyparaphrasedas“Foreveryactionforce,thereisanequal,butopposite,reactionforce”.
Action-ReactionForcesDon’tCancel
Forcepairsdonotcanceleachotherbecausetheyactondifferentobjects
- Touching the side of the pot would result in a burn due to
- Conduction
- Convection
- Radiation
- Stupidity
- Placing your hand above the pot would result in your hand warming due to
- Conduction
- Convection
- Radiation
- If you placed your hand 2 inches away from the side of the pot, it would feel warm due to
- Conduction
- Convection
- Radiation
- Use the graph above to determine the distance the object traveled during 0.4 seconds.
- 1 m
- 0.5 m
- 0.8 m
- 10 m
- The acceleration of the object above is
- 0.5 m/s2
- 1.0 m/s2
- 15 m/s2
- 10 m/s2
- Which system would have more kinetic energy, the one on the left, or the one on the right?
- At position C, the ball has
- Lost kinetic energy but gained potential energy
- Lost potential energy but gained kinetic energy
- Lost both kinetic and potential energy
- Gained both kinetic and potential energy
- At position F, the ball has
- Lost kinetic energy but gained potential energy
- Lost potential energy but gained kinetic energy
- Lost both kinetic and potential energy
- Gained both kinetic and potential energy
- Describe the ball’s motion at position D.
- Decrease the pressure
- Increase the pressure
- Decrease the energy
- Increase the energy
- Both b and d
A60kgwomanand80kgmanpushoffeachotherwhileiceskating.Comparetheforceexperiencedbyeachone.Comparetheaccelerationexperiencedbyeachone.
- What does the following diagram represent? Explain.
- What does the following represent? Explain.
b. Greatest acceleration?
c. Greatest momentum change?
d. Greatest Impulse?
a.Greatest velocity change?
b. Greatest acceleration?
c. Greatest momentum change?
d. Greatest Impulse?