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AP Physics 1

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Unit 1

1.1 Position, Velocity, and Acceleration

5 min readโ€ขoctober 24, 2020

peter57616

Peter Apps


Enduring Understanding 3.A ๐Ÿ‘จโ€๐Ÿ’ป

All forces share certain common characteristics when considered by observers in inertial reference frames. (A frame of reference in which a body remains at rest or moves with constant linear velocity unless acted upon by forces)
Key Vocabulary: Frame of Reference - a point of view ๐Ÿ‘€
โŸถ Motion involves the change in position of an object over a period of time, and it is measured in reference to another object.ย 
EXAMPLE:ย 
Two students are in a classroom sitting at their desks. Are they moving relative to each other?ย 
    • No, both students are stationary relative to each other.
Are they moving relative to the solar system?ย 
  • Yes, they are on Earth and Earth is moving around the sun.ย 

Essential Knowledge 3.A.1 ๐Ÿ˜

An observer in a reference frame can describe the motion of an object using such quantities as position, displacement, distance, velocity, speed, and acceleration.

Position ๐ŸŒŽ

Key Vocabulary: Position - a location relative to a fixed pointย 
โŸถ You can represent position in a Position (m) vs. Time (s) Graph (pictured below)
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-QYShpt4HpBY2.JPG?alt=media&token=39370e5f-7c9d-4e8a-9e53-16cd404cd60e

Image courtesy of ck12.org

Interpreting the Graph
  • To determine which way an object is moving look at which way the Position vs. Time Graph is sloped
    • A front slash / indicates that an object is moving away from the detector
    • A black slash \ indicates that an object is moving towards the detector
  • The slope of a Position vs. Time Graph is equal to velocityย 
    • When the slope is a straight line it has constant velocity
    • When the slope is a curved lived there is acceleration (a change in velocity)
    • When the slope is zero the object is at rest
  • The y-intercept is the initial displacement of an object
โŸถ Still feeling a little confused on Position vs. Time Graphs? Donโ€™t worry! Check out this video from Khan Academy for more practice!ย 

Scalar vs. Vector Quantities ๐Ÿ’ซ

Key Vocabulary: Scalar - quantities that are described by magnitude (a numerical value) aloneย 
Example: She is five feet tall
  • Distance and Speed are scalar quantitiesย 
Key Vocabulary: Vector - quantities that are described by a size (magnitude) and a direction (ex. East, Up, Right, etc.)ย 
Example: The gas station is five miles west from the car
  • Displacement, Velocity, and Acceleration are vector quantities
Vectors can also be represented by arrows, and the length of the arrow should represent the magnitude of the described quantity. From the image below you can see the 5m arrow is smaller in length than the 50m arrow to reflect the difference in magnitude of the two quantities.ย 
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-ef9iscxgL5xK.JPG?alt=media&token=7d62847b-df56-48be-9cf0-e5ec973c2c48
โŸถ Are you still feeling a little confused about Scalar vs. Vector Quantities? Donโ€™t worry! Check out this video from Khan Academy for more practice!ย 

Displacement vs. Distance ๐Ÿšดโ€โ™€๏ธ

Key Vocabulary: Displacement - how far an object is from its original positionย 
  • Vector quantity
  • Express with a Sign (+ or -) or Direction (North, Down, Left, etc.)
  • SI Unit: Meter (m)
  • We use the symbol ฮ”x to indicate displacement
โŸถ Typical Displacement Question: How far are you from home?ย 
Key Vocabulary: Distance - how far an object has traveledย 
  • Scalar quantity
  • Needs no frame of reference
  • SI Unit: Meter (m)
โŸถ Typical Distance Question: How far did you travel?
As you can see from the image below, distance takes into account the journey an object takes whereas displacement is concerned with the frame of reference of the original position.
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FCapture1.PNG?alt=media&token=a4d2ce50-3bc3-4e1f-9b49-e6caaa2ce838

Image Couretsy of thescienceclassroom.org

EXAMPLE:
A car travels 25 meters around a circular track and ends at its original position. What is its distance?
    • Distance โ†’ 25 Meters (The car traveled 25 Meters)
What is its displacement?
    • Displacement โ†’ 0 Meters (The car is 0 Meters from its โ€˜homeโ€™)
โŸถ Still feeling a little confused about Distance vs. Displacement? Donโ€™t worry! Check out this video from Khan Academy for more practice!ย 

Speed vs. Velocity ๐Ÿ‡

Key Vocabulary: Speed - describes how fast a particle is moving
  • Scalar quantity
  • SI Unit: Meters (m)/Seconds (s)
Equation: S = D/t
Key Vocabulary: Velocity - speed in a given direction
  • Vector quantity
  • SI Unit: Meters (m)/Seconds (s)
Equation: V = x/t
โŸถ You can represent velocity in a Velocity (m/s) vs. Time (s) Graph (pictured below)
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FCapture3.PNG?alt=media&token=22c6607f-a8cd-417a-babd-3115ca2fa778

Image Courtesy of ck12.org

Interpreting the Graph
  • To determine which way the object is moving look at whether the Velocity vs. Time Graph is above or below the horizontal axis (x-axis)
    • An object is moving away from the detector if itโ€™s above
    • An object is moving towards the detector if itโ€™s below
  • The y-intercept is the initial velocity of an object
  • The slope of a velocity graph is equal to the accelerationย 
    • When the slope is zero the object has constant velocity
    • When the slope is a straight line it has constant acceleration
    • When the slope is a curved line there is changing acceleration
    • The area under the curve is displacement
    • The object is stopped when y = 0
    โŸถ The table below is a type of motion cheat sheet. Memorizing this will help you ace any quizzes or tests with graph interpretation present!
    Velocity
    Acceleration
    Type of Motion
    V = 0
    A = 0
    At rest
    V = (+) or (-)
    A = 0
    Constant velocity
    V = (+)
    A = (+)
    Speeding up
    V = (-)
    A = (-)
    Speeding up
    V = (+)
    A = (-)
    Slowing down
    V = (-)
    A = (+)
    Slowing down
    FRQ PRACTICE:
    Want more practice with Velocity and Average Velocity? Check out these FRQs from the 2016 AP Physics 1 exam.ย 

    Acceleration ๐Ÿš€

    Key Vocabulary: Acceleration - a change in velocity (magnitude or direction)
    Equation: Aavg = V/t
    โŸถ You can represent acceleration in an Acceleration (m/s/s) vs. Time (s) Graph (pictured below)
    https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-GfqBSDQ9J1ZL.JPG?alt=media&token=d921cbff-d383-443c-9c8e-f1853b666089

    Image courtesy of khanacademy.org

    Interpreting the Graph
    • The y-intercept is the initial acceleration of an object
    • When the slope is zero the object has constant acceleration
    • The area under the curve is velocity
    EXAMPLE:
    (Reference the Graph above to answer the following questions)
    What is the velocity of the object from 0s - 7s?
    • 20 m/s (the area under the curve is 4 x 3 + ยฝ x 4 x 4)
    What is the velocity of the object from 7s - 9s?
    • 2 m/s (the area under the curve is ยฝ x 2 x 2)
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