Describing Motion

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Describing Motion

• Position, velocity, and acceleration

2.12.4
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The Tortoise and the Hare
Told in words, formulas, and graphs
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(No Transcript)
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Group Work

• Describe the Tortoise-and-hare race using a
  position-time graph.

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Tortoise and hare race
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CPS Question

• Who was fastest?
• The tortoise.
• The hare.
• They had the same speed.
• What do you mean by faster?

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Velocity
Rate of changing position
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Poll Question

• Who had the fastest average speed?

1. The tortoise.
2. The hare.
3. Their average speeds were the same.
4. Over what time interval?

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Speed Units
distance
m/s
time
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Velocity as Slope
D distance
Velocity
slope of graph!
D time
distance
D d
D t
time
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Instantaneous velocity
finite Dt
smaller Dt
Young and Freedman, Figure 2.7
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Velocity
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CPS Question

• Who had the fastest maximum instantaneous speed?

1. The tortoise.
2. The hare.
3. Their instantaneous speeds were the same.

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Group Work

• Describe the Tortoise-and-hare race using a
  velocity-time graph.

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Speeds and Areas
speed
area vDt D(distance)
t1
t2
t3
t0
t4
time
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Group Work

• A car waits at a stop light for 5 seconds,
  smoothly accelerates to 15 m/s over 5 seconds,
  and then continues at 15 m/s. Describe the cars
  motion using a speed-time graph.

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Acceleration
Rate of changing velocity
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Poll Question

• What is the SI unit for acceleration?

1. m.
2. s.
3. ms.
4. m/s.
5. m2/s.
6. m/s2.
7. m2/s2.

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Group Work

• In the car scenario
• What is the cars acceleration during the
  different segments of its motion?
• Describe the cars motion using an
  acceleration-time graph.

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Group Work

• Describe four ways (x-t, v-t, a-t, words)

position
0
time
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Group Work

• Describe four ways (x-t, v-t, a-t, words)

velocity
0
time
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Group Work

• Describe four ways (x-t, v-t, a-t, words)

acceleration
0
time