Acceleration

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Acceleration

• For next time Read Chapter 2, Section 5
• Homework SP9, SP10, and
• Ch 2 Q. 6

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How do you move a pencil to create the following
graph?
position
time
3
What is the corresponding velocity versus time
graph?
velocity
time
4
Whats the velocity at t0?
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Graphing velocity
8
6
Velocity (m/s)
4
2
0
3
2
4
5
1
6
0
Time (sec)
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Whats the velocity at t1?
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Graphing velocity
8
6
Velocity (m/s)
4
2
0
3
2
4
5
1
6
0
Time (sec)
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Whats the velocity at t2?
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Graphing velocity
8
6
Velocity (m/s)
4
2
0
3
2
4
5
1
6
0
Time (sec)
10
Whats the velocity at t3?
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Graphing velocity
8
6
Velocity (m/s)
4
2
0
3
2
4
5
1
6
0
Time (sec)
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Whats the velocity at t4?
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Graphing velocity
8
6
Velocity (m/s)
4
2
0
3
2
4
5
1
6
0
Time (sec)
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Graphing velocity
8
6
Velocity (m/s)
4
2
0
3
2
4
5
1
6
0
Time (sec)
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Interpret the slope
8
6
Velocity (m/s)
4
2
0
3
2
4
5
1
6
0
Time (sec)
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Operational definition of acceleration
?v
a

?t
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Constant Acceleration
?t 4 sec
?t 4 sec
v 0 cm/sec
v 20 cm/sec
v 40 cm/sec
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Problem

• A car is moving 50 mph east. Ten seconds later,
  it is moving at 70 mph east. Find the cars
  acceleration (magnitude and direction).

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Problem

• A bear is running at 4 m/s (north). The
  acceleration of the bear is 3m/s2 (north). What
  is the bears velocity 2 seconds later?

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Problem

• A bear is running at 4 m/s (north). The
  acceleration of the bear is 3m/s/s (north). What
  is the bears velocity 2 seconds later?

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What is the acceleration?
-

?t 2s
Vf 6m/s
Vi 9m/s
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Key Point

• Acceleration is a measure of the change in
  velocity that occurs in a unit time interval.

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What is wrong here?

• Acceleration tells how fast the object is moving
  per second.
• Acceleration tells us how much the velocity
  increases.

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Question

• If a -7 m/s/s is it speeding up or slowing
  down?

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What is the acceleration?
-

?t 2s
Vi -6m/s
Vf -9m/s
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Key Point

• An object speeds up when its velocity and
  acceleration have the same direction. An object
  slows down when its velocity and acceleration
  have opposite directions.

29
Without defining a coordinate system, give
examples of the following

• acceleration directed upward, speeding up
• acceleration directed upward, slowing down
• acceleration directed downward, speeding up
• acceleration directed downward, slowing down

30
How do you move a pencil to create the following
graph?
velocity
time
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Homework help.

• Hope it does.

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Reminder Tutorial Homework is due Tuesday.
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Who is passing who?

• You see two cars side-by-side as they exit a
  tunnel on the freeway. The red car has
  velocity of 40 m/s and acceleration of 20
  m/s/s. The blue car has velocity of 20 m/s and
  acceleration of 40 m/s/s.Which car is passing
  the other the instant they leave the tunnel?