大二秋学期物理下课件

0 fx0T0 fx0T=ω mk=2πxf0gxmg §9─3—单 θ<5时,sinθM=-mglsinθ»- d -mglθ= J=dtododtd

=-gl2

ω

dt

=θmcos(ωt+φ T= l

M»-mgld -mglθ=

dt 令ω2

*d2θ+ω2θdt

0θ=θmcos(ωt+φ)T=

§9─4x=Acos(ωt+φ)v=-Aωsin(ωt+φ) =1kx2=1kA2cos2(ωt+φ) =1 =1mv2=1mω2A2sin2(ωtk22ω2=k/=1kA2sin2(ωt+φ)2E=kp=1kA2

=1kA2cos2(ωt+ =1kA2sin2(ωt+φ)E=E=Ek+E1=22x-

φ= Tv-

x=Acosωt E

1kA2 =1kA2cos2 T T

tEk

mωAsin2E EkEp

+A E1mv21kx2 +kx)=0 mvdv+kxdx=0 d2x+dt

x=

mox量为J的薄圆盘与物体m相连，圆盘半径mox mvdvJωdωkxdx mmvdv+Jωdω+kxdx=m 式中ωvdω=1 R \

d2x+Jvd2

+kxv= dt R2 dtd2x(J

+m)+kx=— A2 x2=A2cos(ωt+φ2x=x1+x=Acos(ωt+φ)

1 1 1x A=A2+A2+2AAcos(φ-φ tanφ=A1sinφ1+A2sinA2+A2+A2+2AAcos(φ-φ12 21xx oATt相位差Dφ=2-φ12kπ(xx oATt A=

=1A2+A2+A2+2AAcos(φ-φ12 21= ooA

(k=tA=A1-

φ=φ2A2+A2+A2+2AAcos(φ-φ12 21A=A1+

(k=

φ2-φ1=(2k+1)πAA1 一般情况A1+A2>A>A1-x1=6cos(2t+π x2=8cos(2t-π3)6262+82A2+A2+12

=10tgtg(π-φ)=φπ33688ππφ6x3AAφφ3φ2oxAφφ3φ2ox =A2cos(ωt+φ2 An nx=x+x++ xx=Acos(ωt+φ)ARNOARNO2A0 =Acos =A0cos(ωt+Dφ =Acos(ωt+2Dφ =Acos[ωt+(N-1)Dφ] cosωt

A=2RsinNA0=2R

sinN\A=A

ϕ=1N-1ϕ sin 2 =

cos =A0cos(ωt+Dφ =Acos(ωt+2Dφ)

o

A4 5A A=A=A 0xN=Acos[ωt+(N-1)Dφ 0xN A(1)

2k

3 (k=0,–1,–2,)3论(2NDφ2k

AA2 2x(k'„kN,k'=–1,–2,x

A=A=1 =Acosωt=Acos2πν

x=x1+x2 A1A2ν2-

<<ν1+ν2x=x1+x2=A1cos2πν1t+A2cos2πνx=(2Acos2πν -ν1t)cos2πν

+ν1 x=(2Acos2πν2-ν1t)cos2πν

+ν1 =2

= -ν1(t+T2ν=cos(2πν2-ν1t+π) 2-ν1T T ν2 拍频（合振幅变化的频率ω+φ

ωωt

x A1A A1

+A2+2AA A2A2+A2+2AA12 A

1=

D

-)t= -

ω2>

ω2-

+2A= ν

-ν12

拍频ν

9-6

阻尼力

-kx-Cv=

d2 +kx=0dt 0 ω2d2 ω2 +x=

ω=kδ=C

xω

cos(ωt+φ)ω0-δω2δ20ω0-δω2δ20ω

ifδ2<ω200xxAAe-cosωtOt(φ=AT

>δωω00 <δωω00= =0 ad2 +kx=Fcosω

kmdtx=A0+d2kmdtx=A0+d2 +ω2x=fcosω0p-δtcos(ωt+φ)+Acos(ω