1
Chapter 2Kinematics of Particles
Motions and Coordinates• Motion
– Constrained motion– Unconstrained motion
• Coordinates– Used to describe the motion of particles
2
Motion
Rectilinear motion (1-D)
Plane curvilinear motion (2-D)
Space curvilinear motion (3-D)
CoordinatesRectangular (Cartesian)
coordinates
Normal and tangential coordinates
Polar coordinates
Cylindrical coordinates
Spherical coordinates
),,(),,( zyxyx
)( tn −
),( θr
),,( zr θ
),,( φθr
3
Chapter 2-2. Rectilinear Motion
2
2
Instantaneous velocity
Instantaneous accelerat
:
:
io
n
dsv sdt
dva vdtd v sdt
= =
= =
= =
&
&
&&
vdv adssds sds
=⎧⇒ ⎨ =⎩ & & &&
Graphical Interpretations
4
2 22 1
1 ( ) (the area)2
ads vdv v v= ⇒ − =
a dvv ds=
High School Physics
0
0
2 20 0
20
0 0 0 0
0 0
Given =constant (and ( ) , ( ) , when 0)
(1).
(2).
(3).
2
1
( )
2
v v
a s t s v t v t
dvadt
vdv ads
dsv v a
at
t
v v a s s
s s v atdt
t
= = =
= ⇒
= ⇒
= + =
= +
= + −
= +⇒ +
5
when a≠constant
0
0
0
2 20
00
( ) (1).
(2).
(3).
( ) (1). ( )
( )
1 (
)2
t
os
s
t
v t
v o
dva f t adt
vdv ads
dsvdtd dv dva f v a f vd
v v adt
v v ads
s s v
t tf
d
t v
t
= ⇒ = ⇒
= ⇒
= ⇒
= +
−
= =
=
+
= ⇒ = =
=
⇒ ∫
∫
∫∫
∫
0
0
0 0
0
2 20
0 (2).
( ) (2). 2 ( )
( )
(3).
(
( )
)
v
s t
s
s
s
s
s
v
vdv ds
v v f s
vdv a
ds dt tg s
ds
a f s vdv ads
dsvdt
s s
v s
f
d
v
s
g
= == ⇒
= ⇒ = ⇒
= ⇒= =
+
⇒ =
=
−
∫
∫
∫
∫
∫
Sample 2.1
3
1 1
2 2
( ) 2 24 6
(1). ( ) 72, ?(2). ( ) 30, ( ) ?(3). (4) (3) ?
s t t t
v t tv t a ts s
= − +
= == =− =
6
Problem 2/19
• Small balls fall from rest through the opening at the steady rate of 2 per-second. Find the vertical displacement h of 2 consecutive balls when the lower one has dropped 3 m.
Problem 2/50
• A bumper provides a deceleration as shown in the figure. Suppose a train is approaching the bumper at speed of 40 ft/sec.
• Determine the maximum compression of the bumper.
7
Chapter 2-3. Plane Curvilinear Motion1. 2-D motion: .2. Define the position vector measured from a fixed point .
3. Time derivative of a position vector:
a special case of 3-D
,
rdr dvv r a
t
O
vd dt
= = = =
r
r rr r r r& &
Three coordinates systems to describe the curvilinear motion
Rectangular (Cartesian) coordinates
Normal and tangential coordinates
Polar coordinates
( , )x y
)( tn −
),( θr
8
Chapter 2.4 Rectangular coordinates (x-y)
Vector representation
r xi yj
v r xi yj
a v r xi yj
= +
= = +
= = = +
r rr
r rr r& & &r rr r r& && && &&
0, -Projectile motion: a a gx y= =
9
Sample 2.5
2
( ) 50 16 ,
( ) 100 4 .(0) 0, in meter and in second.
Question :when ( ) 0, ? and ?
xv t t
y t tx y t
y t a v
= −
= −=
= = =
Determine such that is maximized. Rθ
10
Chapter 2.5Normal and Tangential Coordinates (n-t)
• The positive direction of n is always taken toward the center of curvature of the path.
2
2
,
t t t
t t t n
t n
ds ddsv ve e edt
a ve ve ve e
vve e
ρ β
ρβ
ρβ
ρ
=
⇒ = = =
⇒ = + = +
= +
r r r r&
r r r r r& && &
r r&
11
A special case: Circular Motion
22
n
t
v r
va v rr
a r
θ
θ θ
θ
=
= = =
=
&
& &
&&
Write the vector expression for the acceleration of themass G of the simple pendulum in both - and - coordinates for the instance when
o602.00 rad/sec
24.025 rad/sec
a
n t x y
θθθ
==
=
&
&&
12
Exercise 2/119
2 3
A particle moving in the - plane has the position vector as:3 2 ( , ) (in)2 3
Calculate the radius of the path for the position when =2 sec.
x y
P t t
t
=
Chapter 2.6 Polar coordinates (r-θ)
relative to a fixed point
rerrrr
=
13
.2
,
)2()(
,
θ
θ
θθθ
θ
errerra
ererv
err
r
r
r
r&&&&r&&&r
r&r&
r
rr
++−=
+=
=
Sample 2/9
3 2( ) 0.2 0.02 , ( ) 0.2 0.04 .
(3) ? (3) ?
t t t r t t
v a
θ = + = +
= =
14
Exercise 2/145 (slider)
2( ) 0.8 0.05 , ( ) 1.6 0.2 .
(4) ? (4) ? and direction (relative to -axis)
t t t r t t
v a x
θ = − = −
= =
Constant speed =0.6 m/s =1.2 m
, , , , , ?
when 2(1 )3
vR
r r r
t
θ θ θπ=
= +
& &&& &&
15
Chapter 2.7 Space Curvilinear Motion
• Rectangular (x-y-z)• Cylindrical (r-θ-z)• Spherical (R-θ-ψ)
• * n-t coordinates
Rectangular coordinates (x-y-z)
kzjyixRva
kzjyixRv
kzjyixR
r&&
r&&
r&&
&&r&r
r&
r&
r&
&rr
rrrr
++===
++==
++=
16
Cylindrical Coordinates (r-θ-z)
kzerrerrRva
kzererRv
kzerR
r
r
r
r&&
r&&&&r&&&&&r&r
r&
r&r&
&rr
rrr
+++−===
++==
+=
θ
θ
θθθ
θ
)2()( 2
Spherical Coordinates(R-θ-ψ)
φ
θ
φθ
φφθφφ
φθφφφφθ
φθφ
φφθ
eRRR
eRRR
eRRRRva
eReRRv
R
r
r
R
r&&&&
r&&&&&&
r&&&&&&r&r
r&r&r&&rr
rr
)cossin2(
)sin2cos2cos(
)cos(
coseR
eR
2
222
+++
−++
−−===
++==
=
17
Sample 2/11
The power screw starts from rest and is
given a rotational speed which increases
uniformly according to .Suppose the lead of the screw (advancement per revolution) is L. Determine the expressi
θ kt
θ
=
&
&
on for the velocity and acceleration of the center of ball A when the screw has turned through one complete revolution from rest.
Exercise 2/169
• The velocity and acceleration of a particle are given by
• Determine the angle between v and a, , and the radius of curvature.
zyxazyxvrrrr
rrrr
513236
−−=+−=
v&
18
Exercise 2/181
.30
tolowered isit whenboom theof end theof onaccelerati and velocity theof magnitudes theCalculate .sec10
rateconstant at the lowered is boom the time,same At the .min2 of rateconstant a at axis vertical
about the turningis and ,24 lengthof booma has crane revolving The
o
rad/.
rev/
m
Chapter 2.8 Relative Motion
/ ,
/ ,
/ ,
A B A B
A B A B
A B A B
r r r
v v v
a a a
= +
= +
= +
19
Sample 2/12
o
o
Flight A is moving east at a speed of 800 km/hFlight B is moving northeast
(45 ) at a speed Passengers at flight A observe that flight B moves northwest
(60 ).Determine ?
v
v =
Exercise 2/188
cars? theof velocities theconcerning said be can
What cars. theofvelocity relative theof magnitude
theequals cars thebetween distance theof increase of rate time theIf roads.straight along
moving are Band A cars Two
20
Exercise 2/194
• A ship is capable of 16 knots through still water is to maintain a true course due west while encountering a 3-knots current running from north to south. What should be the heading of the ship (measured clockwise from the north to the nearest degree)? How long does it take the ship to proceed 24 nautical miles due west?
Chapter 2.9 Constrained Motion
0202
2
=+=+=+
yxyx
kyx
&&&&
&&
21
02020202
22
2
1
=+−=+=+−=+=+−=+
cDB
DA
cDB
DA
cDB
DA
yyyyyyyyyy
kyyykyy
&&&&&&
&&&&
&&&
&&
Sample 2/15
The tractor is used to hoist the bale with the pulley arrangement shown. If has a forward velocity , determine an expression for the upward velocity of the bale in termsof .
A
B
AB
AV
Vx
22
Exercise 2/207
If block has a leftward velocity of 1.2 m/s, determine the velocityof cylinder .
B
A
Exercise 2/220
The particle is mounted on a loght rod pivoted at andtherefore is constrained in a curvelar arc of radius . Determine the velocity of in terms of the downward velocity of the counterweight fo
B
A O
rA
v r any angle .θ
23
Chapter Review
• Motion– Rectilinear motion (1-D)– Plane curvilinear motion (2-D)– Space curvilinear motion (3-D)
• Coordinates– Rectangular (Cartesian) coordinates
– Normal and tangential coordinates
– Polar coordinates
– Cylindrical coordinates
– Spherical coordinates
),,(),,( zyxyx
)( tn −
),( θr
),,( zr θ
),,( φθr