C H A P T E R
2
Kinematics in One
Dimension
Mechanics
The study of
Physics
begins with mechanics.
Mechanics
The study of
Physics
begins with mechanics.
Mechanics
is the branch of physics that focuses on the motion
of objects and the forces that cause the motion to change.
Mechanics
The study of
Physics
begins with mechanics.
Mechanics
is the branch of physics that focuses on the motion
of objects and the forces that cause the motion to change.
There are two parts to mechanics:
Kinematics
and
Dynamics
.
Mechanics
The study of
Physics
begins with mechanics.
Mechanics
is the branch of physics that focuses on the motion
of objects and the forces that cause the motion to change.
There are two parts to mechanics:
Kinematics
and
Dynamics
.
Kinematics
deals with the concepts that are needed to describe
motion, without any reference to forces.
Chapter 2: Kinematics in one dimension
Chapter 3: Kinematics in two dimensions
Mechanics
The study of
Physics
begins with mechanics.
Mechanics
is the branch of physics that focuses on the motion
of objects and the forces that cause the motion to change.
There are two parts to mechanics:
Kinematics
and
Dynamics
.
Kinematics
deals with the concepts that are needed to describe
motion, without any reference to forces.
Chapter 2: Kinematics in one dimension
Chapter 3: Kinematics in two dimensions
Dynamics
deals with the effect that forces have on motion.
Chapter 4: Dynamics
Distance and Displacement
Distance and Displacement
Starting from origin, O a person walks 90

m east, then turns
around and walks 40

m west.
Distance and Displacement
Starting from origin, O a person walks 90

m east, then turns
around and walks 40

m west.
Q: What is the total walked distance?
Distance and Displacement
Starting from origin, O a person walks 90

m east, then turns
around and walks 40

m west.
Q: What is the total walked distance? A: 130

m
Distance and Displacement
Starting from origin, O a person walks 90

m east, then turns
around and walks 40

m west.
Q: What is the total walked distance? A: 130

m
Q: What is the displacement?
Distance and Displacement
Starting from origin, O a person walks 90

m east, then turns
around and walks 40

m west.
Q: What is the total walked distance? A: 130

m
Q: What is the displacement? A: 50

m, due east.
Displacement
position
initial
o
x
position
final
x
nt
displaceme
o
x
x
x
The
displacement
Ä
x
is a
vector
that points from the initial position
to the final position
.
SI Unit of Displacement:
meter (m)
Figure 2

2
One

Dimensional Coordinates
2.2 Speed and Velocity
•
Average Speed
•
Average Velocity
•
Instantaneous Velocity
•
Instantaneous Speed
Average Speed
Units for speed: m/s, MPH, kmPH.
Conceptual Checkpoint 2

1
Average Speed
Average Velocity
t
t
t
o
o
x
x
x
v
Units for velocity: m/s, MPH, kmPH.
time
Elapsed
nt
Displaceme
velocity
Average
Figure 2

6
Constant Velocity on an
x

Versus

t
Graph
Example 2

2
Sprint Training
Figure 2

4
Motion Along the
X
Axis Represented with an
x

Versus

t
Graph
Figure 2

5a
Average Velocity on an
x

Versus

t
Graph
Figure 2

5b
Average Velocity on an
x

Versus

t
Graph
Instantaneous Velocity and Speed
The
instantaneous velocity
v
indicates how fast an object
moves and the direction of the motion at each instant of time.
t
t
x
v
0
lim
The magnitude of the instantaneous velocity is called the
instantaneous speed
, and it is the number (with units) indicated
by the speedometer.
Figure 2

7
Instantaneous Velocity
Figure 2

8
Graphical Interpretation of Average and Instantaneous Velocity
Acceleration
Acceleration
Units: m/s
2
, cm/s
2
Table 2

3
Typical Accelerations (m/s
2
)
Ultracentrifuge
3 x 10
6
Batted baseball
3 x 10
4
Bungee jump
30
Acceleration of gravity on Earth
9.81
Emergency stop in a car
8
Acceleration of gravity on the Moon
1.62
Figure 2

9
v

Versus

t
Plots for Motion with Constant Acceleration
Example 2

3
An Accelerating Train
Instantaneous acceleration
Acceleration at a particular instant is called instantaneous
acceleration.
Figure 2

10
Graphical Interpretation of Average and Instantaneous Acceleration
Deceleration
Deceleration
An object speeds up when the acceleration and velocity vectors
point in the same direction.
Deceleration
An object speeds up when the acceleration and velocity vectors
point in the same direction.
Whenever the acceleration and velocity vectors have opposite
directions, the object slows down and is said to be “decelerating.”
Figure 2

11
Cars Accelerating or Decelerating
Deceleration
An object speeds up when the acceleration and velocity vectors
point in the same direction.
Whenever the acceleration and velocity vectors have opposite
directions, the object slows down and is said to be “decelerating.”
Example 4: A drag racer crosses the finish line, and the driver
deploys a parachute and applies the brakes to slow down. The
driver begins slowing down when
t
0
= 9.0 s and the car's
velocity
is
v
0
= +28 m/s. When
t
= 12.0 s, the velocity has been reduced to
v
= +13 m/s. What is the average
acceleration
of the dragster?
Kinematics Equations
Figure 2

13a
The Average Velocity
Figure 2

14
Velocity Versus Time for the Boat in Example 2

5
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