Xem mẫu
- r
at
KÕt luËn
r
r
an
rrr
a = at + an a 1
®é cong
R cña quÜ
2
®¹o
dv 2 v2
a= + = ( ) +( )
2 2
at an
dt R
• an=0 -> chuyÓn ®éng th¼ng
• at=0 -> chuyÓn ®éng cong ®Òu
• a=0 -> chuyÓn ®éng th¼ng ®Òu
- 4. Mét sè d¹ng chuyÓn ®éng c¬ ®Æc biÖt
4.1. ChuyÓn ®éng th¼ng biÕn ®æi ®Òu:
r v2-v20=2as
a = const a n = 0 M
O
dv
a = at = = const
v = ∫ adt = at + v 0
dt
2
ds at
= at + v 0 ⇒ s = ∫ (at + v 0 )dt =
v= + v0t
dt 2
M’
4.2. ChuyÓn ®éng trßn
T¹i M: t
Δθ M
T¹i M’: t’=t+Δt => OM quÐt Δθ O
Δθ Δ θ dθ 2π ω
1
ω= ω = lim Δt→0 = T= ; ν= =
Δt dt
Δt ω T 2π
- r r r
Quan hÖ gi÷a ω vμ v ω
(
M M = Δ s = R .Δ θ
r
Or
Δs Δθ v
R
= lim Δt→0 R. = R.ω
lim Δt→0
Δt Δt
rrr
v = R.ω ⇒ v = ω × R Qui t¾c tam diÖn thuËn
( Rω)
2 2
HÖ qu¶: v
an = = = Rω 2
R R
r
t, ω
Gia tèc gãc: T¹i rr r
T¹i M’: t ' = t + Δt, ω' = ω + Δω
Δω dω d θ 2
β = lim Δt→0 = =2
Δt dt dt
- r r
r Δω dω r
r ω
β = lim Δt→0 =
ω Δt
r dt
rr
β r
r
at = β × R r
O r at r Or
v
Rr
v
R r aM
M
Qui t¾c tam diÖn thuËn β t
T−¬ng tù nh− trong chuyÓn ®éng th¼ng:
ω = βt + ω0
βt 2
θ= + ω0 t
2
ω − ω0 = 2βθ
2 2
- 4.3. ChuyÓn ®éng víi gia tèc kh«ng ®æi
yr
r a =0
r v0
ax
ay=-g v 0y hmax
αr
dv x
=0 O v 0x x
dt
Ph−¬ng tr×nh chuyÓn ®éng
dv y
= −g
x = v 0 cos α.t
dt
v x = v 0 cos α 2
M gt
y = v 0 sin α.t −
v y = v 0 sin α − gt 2
2
gx
Ph−¬ng tr×nh quÜ ®¹o y = xtgα −
2 v 0 cos α
2 2
- 4.4. Dao ®éng th¼ng ®iÒu hoμ
ph−¬ng tr×nh dao ®éng x
0
x = A. cos( ωt + ϕ)
TuÇn hoμn theo thêi gian: x(t)=x(t+nT)
2π
T=
ω
dx
v= = − ωA. sin( ωt + ϕ)
dt
2
dv d x
a= = 2 = − ω A. cos( ωt + ϕ)
2
dt dt
nguon tai.lieu . vn
