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Physics 121 9/10/10
Prof. E. F. Redish 1
9/10/10 1 Physics 121
9/10/10 3 Physics 121
9/10/10 4
o Choose origin
o Choose axes
o Choose scale
o Set scales on graph
o Take data from video
Physics 121
Physics 121 9/10/10
Prof. E. F. Redish 2
9/10/10 8
r t( ) = x(t)ˆ i + y(t) ˆ j
x(t)
r =
r t2( )
r t1( )
t = t2 t1
Physics 121
9/10/10 9
r t r t r t
r r t r t
r r t r t
r r r
r t r t r t r t
r t r t
( ) ( ) ( )
( ) ( )
( ) ( )
( ) ( ) ( ) ( )
( ) ( )
1 2 3
12 2 1
23 3 2
13 12 23
2 1 3 2
3 1
=
=
= +
= +
= Physics 121
9/10/10 10 Physics 121
< > =
< > =
v
vr
t
displacement
time it took to make the displacement
Physics 121 9/10/10
Prof. E. F. Redish 3
9/10/10 11 Physics 121
< > = =
=
=
= +
vr
tv
r v t
r t r t v t
r r v tfinal initial
0
0
2 1 0
0
( ) ( )
Position as a function of time
0
2
4
6
8
10
-5 0 5 10 15
t (sec)
x (
m)
9/10/10 16 Physics 121
9/10/10 17 Physics 121
Physics 121 9/10/10
Prof. E. F. Redish 4
9/10/10 18 Physics 121
v tdr
dt
v tr t r t
t
t t
( )
( )( ) ( )
=
=+ 2 2
9/10/10 19 Physics 121
9/10/10 20 Physics 121
Physics 121 9/10/10
Prof. E. F. Redish 5
9/10/10 23 Physics 121
Velocity as a function of time
0
0.5
1
1.5
2
-5 0 5 10 15
t (sec)
x (m
)
Position as a function of time
0
2
4
6
8
10
-5 0 5 10 15
t (sec)
x (
m)
v =x
tx = v t
x
t
Slope
= <v>
v (
m/s
)
9/10/10 24 Physics 121
9/10/10 26 Physics 121
t (sec)
x (m)
t (sec)
v (m)
dx
dt
v
v =displacement
time it took to make the displacement
v =x
tx = v t
