A) 1.0 m
B) 7.0 m
C) 3.0 m
D) - 1.0 m
E) - 7.0 m
18
Describing motion(1.Motion Diagrams,2.Graphs,3.Equations);
Position and displacement;
Velocity;
Acceleration; Free Fall
•
Constant Average Velocity and Uniform
Motion:
•
Uniform motion
: Characterized by equal
displacements in equal time intervals=
Constant velocity
. Straight line in
position vs. time graph.
•
Slope = rise/run = change in pos./time
interval. This is the average velocity.
(Unit: m/s)
i
f
i
f
avg
t
t
x
x
t
x
v
−
−
=
Δ
Δ
=
x
t

7
19
Which position-versus-time graph represents the
motion shown in the motion diagram?
(A)
(B)
(C)
(D)
(E)
Question
20
Describing motion(1.Motion Diagrams,2.Graphs,3.Equations);
Position and displacement;
Velocity;
Acceleration; Free Fall
– Curved parts in position
vs. time graph
– The average velocity in
time interval t
2
– t
1
is
1
2
1
2
t
t
x
x
t
x
v
avg
−
−
=
Δ
Δ
=
•Non-Uniform Motion
characterized by an
acceleration or deceleration:
21
Describing motion(1.Motion Diagrams,2.Graphs,3.Equations);
Position and displacement;
Velocity;
Acceleration; Free Fall
dt
dx
t
x
v
t
=
Δ
Δ
=
→
Δ
0
lim
•
Can we determine the instantaneous velocity at a single point in
time from the graph
•
In a plot of the position vs. time, the instantaneous velocity is
the slope (or tangent) at every point of the curve.

8
22
Describing motion(1.Motion Diagrams,2.Graphs,3.Equations);
Position and displacement; Velocity;
Acceleration
; Free Fall
•
In a plot of the
velocity vs. time
, the acceleration
is the
slope
at every point of the curve.
•
Average acceleration = change in velocity in time
interval
Δ
t:
•
SI unit: m/s
2
•
Phys 100: Constant acceleration, so a = a
avg
.
i
f
i
f
avg
t
t
v
v
t
v
a
−
−
=
Δ
Δ
=
v
t
t
i
t
f
v
f
v
i
23
Question
•
When an object is slowing down (deceleration),
what happens?
– (Hint: think of a ball tossed up vertically.)
A) There is no acceleration.
B) There is not enough acceleration.
C) Acceleration and velocity are in opposite
directions.
D) None of the above.
24
Question
•
If you toss a ball up, at the highest point
A.
The velocity changes direction.
B.
The acceleration changes direction.
C.
The acceleration is zero.
D.
Both velocity and acceleration are zero.
E.
More than one of the above is correct.

9
25
Problem
-25
-20
-15
-10
-5
0
5
10
15
20
25
0
5
10
15
20
Time (min)
Velocity (km/h)
•
The graph shows your bike trip to the coffee shop.
What is the displacement and the total distance?
26
Solution
-25
-20
-15
-10
-5
0
5
10
15
20
25
0
5
10
15
20
Time (min)
Velocity (km/h)
•
The graph shows your bike trip to the coffee shop.
What is the displacement and the total distance?

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- Spring '09
- Lioudmila
- Acceleration, Velocity, Vavg