Acceleration
Acceleration
• The rate of change in velocity
Acceleration
• The rate of change in velocity
• Examples….
– Speeding up
• Positive acceleration
– Slowing down
• Negative acceleration
• Deceleration
– Changing direction
• Centripetal acceleration
Acceleration
• Compare to speed
• Acceleration is the rate of change in either
speed or direction, while speed is the rate
of change in position. They are both rates,
but they are rates of different things.
Acceleration
• Formula for calculating acceleration:
finalvelocity  startingvelocity
acceleration 
time
vf  vs
a
t
Acceleration
• Formula for calculating acceleration:
Vf = final velocity
Vs = starting velocity
t= time
a = acceleration
vf  vs
a
t
Acceleration
• One last way to write that formula:
• Which is read delta v over t or change in
velocity over time.
a 
v
t
Acceleration: Example
• What is the average acceleration of a
subway train that speeds up from 6 m/s to
12 m/s in 2s?
vf  vs
a
t
Acceleration: Example
• What is the average acceleration of a
subway train that speeds up from 6 m/s to
12 m/s in 2s?
Vf = 12 m/s
a=?
Vs = 6 m/s
t= 2 s
Acceleration Problems
What is the average acceleration of a subway
train that speeds up from 6 m/s to 12 m/s in 2s?
vf = 12 m/s
vs = 6 m/s
t = 2s
12m / s  6m / s
a
2s
6m / s

2s
 3m / s / s
Acceleration Problems
A person is traveling at 20 m/s in a car when
the car hits a tree. The person comes to a
complete stop in 0.4 seconds. What was the
person’s acceleration?
Acceleration Problems
A person is traveling at 20 m/s in a car when
the car hits a tree. The person comes to a
complete stop in 0.4 seconds. What was the
person’s acceleration?
vs = 20 m/s
vf = 0 m/s
t = 0.4s
vf  vs
a
t
Acceleration Problems
A person is traveling at 20 m/s in a car when
the car hits a tree. The person comes to a
complete stop in 0.4 seconds. What was the
person’s acceleration?
vs = 20 m/s
vf = 0 m/s
0m / s  20m / s
a
t = 0.4s
0 .4 s
 20m / s

0.4 s
 50m / s / s
Recognizing acceleration on a
graph
This graph shows positive
acceleration because the
object is getting faster.
The distance traveled in
each second is
increasing. The graph is
becoming more steep.
Distance
(m)
Recognizing acceleration on a
graph
Time (s)
This graph shows
negative acceleration
because the object is
getting slower. The
distance traveled each
second is decreasing.
The graph is getting less
steep.