Announcements:
 Selfie, book number, etc….?
 Lab donation?
 2L bottles?
 Unit I-1 Exam: Friday, Unit I-1 HW due Monday
 Phet: Vector Addition due by midnight, Phet: Moving
Man due tomorrow
 Turnitin:
 Password- apphys12
 Class ID- 10276991
Unit I-1:
Kinematics in 1D and 2D
Part 2- Acceleration
Acceleration
 The rate (1/Dt) of change of velocity
(Dv)
 Since velocity is a vector quantity,
acceleration is also a vector quantity.
 Three types of acceleration
 Average
 Constant
 Instantaneous
Average Acceleration
 Rate of change of velocity = acceleration
CARD!
v
-v
Dv
a=
= f i
t
t
Example: A plane can go from rest to 30 m/s in 10 s.
What is it’s acceleration?
Note: a can be positive or negative, since time can’t be
negative the sign of a indicates Dv
Graphs of acceleration
Graphically
Algebraically:
v
-v
Dv
a=
= f i
t
t
CARD!
vf = vi + at
Displacement during constant
acceleration
Dd
v=
t
d = vt
final
✖
vavg = vf + vi
2
But which v is that?
initial
✖
average ✔
d = ½ (vf + vi)t
CARD!
Displacement when acceleration and
time are known
vf = vi + at
d = ½ (vf + vi)t
d = ½ ((vi + at) + vi)t
d = ½ (2vi + at)t
d = vit +
2
½at
CARD!
Example:
 A boat at rest accelerates at 4.2 m/s2 for 14 s. What is
it’s displacement?
Displacement when acceleration and
velocity are known
d = ½ (vf + vi)t
d = ½ (vf + vi)(vf - vi)
a
d = ½ (vf2 - vi2)
a
2
vf
=
2
vi
vf = vi + at
- vi
t = vf a
+ 2ad
CARD!
Example:
A plane is landing with a velocity of m/s and a maximum
acceleration of -2.5 m/s2. How much runway will it
require?
6 Basic Kinematic Equations
Dv
Dd
a=
v=
t
t
vf = vi + at No d
d = ½ (vf + vi)t
No a
d = vit + ½at2
No vf
vf2 = vi2 + 2ad
No t
Gravity
 Galileo determined that things fall with constant
acceleration.
 Acceleration due to gravity = -9.8 m/s2
 Up is defined as the positive direction.
 So “g” can be substituted for “a” in any of the basic
kinematic equations.
Example:
 A kangaroo jumps to a vertical height of 2.8 m. How
long was he in the air?