功与动能定理：电场力做功与动能、势能关系分析.pdfVIP

Lecture1:2WorkandKineticEnergy—

ConceptTheorem

1.Electricfield

forcework

1.:

TheworkofelectricfieldforceEqdFdFW=θ==xcos,disthediscementalongthedirectionofthe

electricfieldline,|AM|inthefigurebelow.

2.Note:

(1)Inauniformelectricfield,theworkdonebytheelectricfieldforcehasnothingtodowiththepath,but

onlywithdinthedirectionoftheelectricfieldline.

3.TwomethodsofderivingEqdW=:

(1)AccordingtoW＝FS

(2)Accordingtofunctional

relationship

二.重力场中，

物体自由下落，重力做正功，V增大，动能增大，重力势能减小；

物体自由上抛，重力做负功，V减小，动能减小，重力势能增大。

三.电场力功、动能、电势能

1.正电荷

（1）A→B，（正功，V增大，动能增大，电势能减小。）

（2）B→A，（负功，V减小，动能减小，电势能增大。）

2.负电荷

（1）A→B，（负功，V减小，动能减小，电势能增大。）

（2）B→A，（正功，V增大，动能增大，电势能减小。）

同一电场中，同样的两点间（例如A→B），移动正电荷、负电荷，电荷电势能的变化是相反的。

2.Inthegravity

field,

Whenanobjectfallsfreely,gravitydoespositivework,Vincreases,kineticenergy

increases,andgravitypotentialenergydecreases;whenanobjectisfreelythrownup,

gravitydoesneivework,Vdecreases,kineticenergydecreases,andgravity

potentialenergyincreases.

3.Electricfieldforcework,kinetic

energy,andpotentialenergy

1.Positive

charge

(1)A→B,(positivework,Vincreases,kineticenergyincreases,andpotential

energydecreases.)(2)B→A,(neivework,Vdecreases,kineticenergy

decreases,andpotentialenergyincreases.)

2.Neive

charge

(1)A→B,(Neivework,Vdecreases,kineticenergydecreases,andpotential

energyincreases.)

(2)B→A,(positivework,Vincreases,kineticenergyincreases,andpotentialenergy

decreases.)

Inthesameelectricfield,weenthesametwopoints(forexample,A→B),thepositiveandneivechargesaremoved,andthec

hangeofthechargepotentialenerg