Motion 11.3 Acceleration

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Motion11.3 Acceleration

• Chapter 11

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What are we going to learn?

• What is acceleration?
• How to calculate acceleration
  and interpret speed vs. time
  graphs

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Acceleration

• Rate at which velocity changes

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Acceleration

• Can be described as changes in speed, direction,
  or both

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• It is a vector
• 2 types constant and free fall

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• This change may be due to either an increase or a
  decrease in speed
• Positive increasing change in speed
• Negative decreasing change in speed

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Acceleration Animation

• http//www.physicsclassroom.com/mmedia/kinema/avd.
  cfm
• http//www.physicsclassroom.com/mmedia/kinema/acce
  ln.cfm

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Constant Acceleration

• A steady change in velocity

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• If the velocity increases, the numerator is
  positive so acceleration is positive
• If the velocity decreases, the numerator
  isnegative so acceleration is negative

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Free Fall

• Movement of an object
  toward Earth solely
  because of gravity
• Due to change in speed
• Rate of change in speed is 9.8 meters per second
  per second (9.8 m/s2)

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Changing Direction

• Acceleration may be due to its direction
  constantly changing even though it is traveling
  at constant speed
• Ex horse on a carousel

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Changing Direction Speed

• Sometimes motion is changing in both speed and
  direction at the same time
• Ex skier on a downhill run

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Acceleration Calculation

• Calculation for straight-line motion divide the
  change in velocity by the total time

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• This equation defines the average acceleration
• A change in velocity by a constant amount each
  second (its position changes by a constant amount
  each second)

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Acceleration Graphs

• Acceleration is the slope of a speed-time graph

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• In a linear graph, the displayed data form
  straight-line parts

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• In a nonlinear graph, a curve connects the data
  points that are plotted

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Instantaneous Acceleration

• How fast a velocity is changing at a specific
  instant

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Example

• A snow skier is traveling at 15 m/s at one
  instant and at 22 m/s 2 seconds later. What is
  her acceleration?

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• If she maintains this constant acceleration, how
  fast will she be traveling one second later?

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Acceleration Graph
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Questions...
Acceleration
is a change in
is measuredin units of
direction
speed
m/s2
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• The rate at which velocity changes is called
  acceleration.

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• In terms of speed and direction, in what ways can
  an object accelerate?
• Increase or decrease speed, change direction,
  or both change speed and direction.

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• Because acceleration is a quantity that has both
  magnitude and direction, it is a(n) vector.

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• True or false? Acceleration is the result
  ofincreases or decreases in speed. True

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• Ignoring air resistance, a rock in free fall will
  have a velocity of 39.2 m/s after 4.0 seconds.
• (9.8 m/s2)(4.0 s)

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• A horse on a carousel that is moving at a
  constant speed is accelerating because it is
  constantly changing direction

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• Write the equation used to calculate the
  acceleration of an object .
• Acceleration change in velocity divided by the
  total time

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• True or false? When the final velocity isless
  than the initial velocity of an object, the
  acceleration is negative. True

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• A skateboarder begins down a ramp at a speed of
  1.0 m/s. After 3 seconds, her speed has increased
  to 4.0 m/s. Calculate her acceleration.
• a. 1.0 m/s2 b. 3.0 m/s2
• c. 5.0 m/s2 d. 9.8 m/s2

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• Graph A represents the
  motion of a downhill skier. How fast was the
  skier moving after traveling down the hill for
  2.5 seconds?
• 10 m/s

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• In which graph does an object move at constant
  speed during the first 4 seconds?
• Graph B

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• Graph B represents the motion of a mountain
  biker. What is the bikers speed at times of 10 s
  and 20 s?

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• Graph B represents the motion of a mountain
  biker. What is the bikers speed at times of 10 s
  and 20 s?
• 5 m/s
• 0 m/s

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• Determine the acceleration of the mountain biker
  during the 10 second to 20 second time period.
  Show your work.
• 0 m/s 5 m/s - 5 m/s -0.5 m/s2
• 20 s 10 s 10 s

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• The plotted data points representing acceleration
  in a distance-time graph form a(n) curved line.

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• The measure of how fast a velocity is changing at
  a specific instant is known as instantaneous
  acceleration.