Bell Ringer

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Bell Ringer

• Monday 8/31/09
• 1. A cheetah ran a distance of 274 m in 8.65s
  toward an antelope. What is the velocity of the
  cheetah?
• 2. What does it mean for an object to have an
  acceleration?

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Acceleration

• Science 1A

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Changes in Velocity

• Changes in velocity include
• Speeding up
• Slowing down
• Any change in direction
• Any change in velocity is called an Acceleration!

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Acceleration

• The acceleration of an object then is its change
  in velocity over a certain period of time.

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• We calculate acceleration by the following
  equation
• Acceleration (a)
• final velocity initial velocity
• time
• a Dv
• t

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Dv final v initial v

• The SI unit for acceleration is
• Meters per second per second
• m/s2

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Acceleration Values

• Acceleration values may be positive or negative.
• Positive acceleration means that the object is
  speeding up.
• Negative acceleration means that the object is
  slowing down.

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Acceleration Values cont.

• A small acceleration value means that speed is
  increasing or decreasing slowly.
• A large acceleration value means that speed is
  increasing or decreasing rapidly.

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Acceleration Cont

• An object at constant velocity has no
  acceleration it is not speeding up, slowing
  down or changing direction!

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Lets Practice!

• A flowerpot falls off a second-story windowsill.
  The flowerpot starts from rest and hits the
  sidewalk 1.5 s later with a velocity of 14.7 m/s.
  Find the average acceleration of the flowerpot.

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• List the given and unknown values.
• Given time, t 1.5 s
• initial velocity, initial v 0 m/s down
• final velocity, final v 14.7 m/s down
• Unknown acceleration, a ? m/s2 down

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• Write the equation for acceleration.
• Acceleration (a)
• final velocity initial velocity
• time
• a Dv
• t

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• Insert the known values and solve.
• a Dv (final v initial v)
• t t
• (14.7 m/s 0 m/s)
• 1.5 s
• a 14.7 m/s 9.8 m/s2 down
• 1.5 s

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Now you get to practice!
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• Natalie accelerates her skateboard along a
  straight path from 0 m/s to 4.0 m/s in 2.5 s.
  Find her average acceleration.

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• Natalie accelerates her skateboard along a
  straight path from 0 m/s to 4.0 m/s in 2.5 s.
  Find her average acceleration.
• 1.6 m/s2 along her path

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• A turtle swimming in a straight line toward the
  shore has a speed of 0.50 m/s. After 4.0 s, its
  speed is 0.80 m/s. What is the turtles average
  acceleration?

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• A turtle swimming in a straight line toward the
  shore has a speed of 0.50 m/s. After 4.0 s, its
  speed is 0.80 m/s. What is the turtles average
  acceleration?
• .075 m/s2 toward the shore

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• Find the average acceleration of a northbound
  subway train that slows down from 12 m/s to 9.6
  m/s in 0.8 s.

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• Find the average acceleration of a northbound
  subway train that slows down from 12 m/s to 9.6
  m/s in 0.8 s.
• -3 m/s2 north

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• Marissas car accelerates at an average rate of
  2.6 m/s2. Calculate how long it takes her car to
  accelerate from 24.6 m/s to 26.8 m/s.

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• Marissas car accelerates at an average rate of
  2.6 m/s2. Calculate how long it takes her car to
  accelerate from 24.6 m/s to 26.8 m/s.
• 0.85 s

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Motion Graphs

• When the motion of an object is graphed by
  plotting the distance it travels versus time, the
  slope of the resulting line is the objects
  speed.

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• Data for a Bicycle at Constant Speed

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• Data for a Bicycle at Constant Velocity

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• Data for a Slowing Bicycle (Speed)

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• Data for a Slowing Bicycle

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Acceleration Lab

• Work with a partner
• Read through the directions
• Get the materials
• Begin the lab

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Class work

• Acceleration Worksheet
• Acceleration (a) final velocity initial
  velocity
• time