Motion 11.1 Distance and Displacement

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Motion11.1 Distance and Displacement

• Chapter 11

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What are we going to learn?

• Methods of describing motion
• How can vectors be combined?

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A story of motion...

• Once upon a time, 3 students (George, Harry, and
  William) were on their way to school. When asked
  the question, How fast are your friends moving?
  there were very different and conflicting answers
  from the students.

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• George says that Harry and William are moving
  very fast.
• Harry says that George is moving but William is
  not.
• William says that George is moving but Harry is
  not.

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• If everyone is telling the truth, how can this be?

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• Its all a matter of frame of reference...
• Hint........

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• George is standing waiting at the bus stop. Harry
  and William are already on a moving bus.

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Frame of Reference

• Necessary to describe motion accurately and
  completely
• A system of objects that are not moving with
  respect to one another

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Relative Motion

• Movement in relation to a frame of reference
• More on this later.....

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Distance

• Length of the path between two points

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Distance Units

• SI unit for distance meter (m)
• For very large distances kilometers (km)
• For distances smaller than meters centimeters
  (cm)

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Displacement

• Direction from the starting point and the length
  of a straight line from the starting point to the
  ending point
• Gives information both about how far away an
  object is from a given point and
  in what direction the object is
  from that point
• Displacement is a vector

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Vectors

• A quantity that has direction and magnitude (can
  be size, length, or amount)
• Add displacements using vector addition

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Vector Addition

• When two vectors have the same direction, you can
  add their magnitudes

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• When two vectors are in opposite directions,
  subtract one magnitude from the other
• Ex A police officer going the speed limit of 45
  mph clocks you going in the opposite direction at
  92 mph. Do you get a ticket?

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• Since the vehicles are going in opposite
  directions, subtract the police officer vector
  from your vehicle vector...the answer is your
  unknown speed
• 92 mph 45 mph 47 mph
• (2 mph over the speed limit)

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• When two or more vectors have different
  directions, combine them by graphing

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Vector Addition

• Sum of two or more vectors is the resultant
  vector

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Review Questions

• What two things must you know to describe the
  motion of an object?

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Review Questions

• What two things must you know to describe the
  motion of an object?
• Frame of reference and direction

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• True or false?
• A frame of reference is not necessary to
  describe motion accurately and completely.

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• True or false?
• A frame of reference is not necessary to
  describe motion accurately and completely.
• False, frame of reference is necessary to
  accurately describe motion

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• True or false?
• Five blocks south is an example of a
  displacement.

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• True or false?
• Five blocks south is an example of a
  displacement.
• True

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• Circle the letter of the SI unit best suited for
  measuring the length of a room in your home.
• a. kilometers b. meters
• c. centimeters d. millimeters

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• Circle the letter of the SI unit best suited for
  measuring the length of a room in your home.
• a. kilometers b. meters
• c. centimeters d. millimeters

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• Imagine that you are a passenger in a car. Circle
  the letter of the best frame of reference you
  could use to determine how fast the car is moving
  relative to the ground.
• a. the people sitting next to you in the
  backseat
• b. the driver of the car
• c. a van traveling in the lane next to your car
• d. a sign post on the side of the road

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• Imagine that you are a passenger in a car. Circle
  the letter of the best frame of reference you
  could use to determine how fast the car is moving
  relative to the ground.
• a. the people sitting next to you in the
  backseat
• b. the driver of the car
• c. a van traveling in the lane next to your car
• d. a sign post on the side of the road

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• What would your total displacement be if you
  walked from your front door, around the block,
  and then stopped when you reached your front door
  again?
• a. one block b. two blocks
• c. the entire distance of your trip d. zero

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• What would your total displacement be if you
  walked from your front door, around the block,
  and then stopped when you reached your front door
  again?
• a. one block b. two blocks
• c. the entire distance of your trip d. zero

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• Compare and contrast distance and displacement.

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• Compare and contrast distance and displacement.
• Same both describe measurement of motion
• Different distance is a straight line
  measurement between 2 points
• displacement includes direction
  and a straight line measurement from starting
  point to finish point

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• A vector is a quantity that has both
  ______________ and ______________.

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• A vector is a quantity that has both magnitude
  and direction.

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• The vector sum of two or more other vectors is
  called the _________________________.

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• The vector sum of two or more other vectors is
  called the resultant vector.

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• Circle the letter of each answer that could
  describe the magnitude of a vector.
• a. length b. direction c. amount d.
  size

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• Circle the letter of each answer that could
  describe the magnitude of a vector.
• a. length b. direction c. amount d.
  size

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• Because the two displacements are in opposite
  directions, the magnitude of the total
  displacement is ________________________ .

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• Because the two displacements are in opposite
  directions, the magnitude of the total
  displacement is addition of opposite vectors with
  a total displacement of 4 km.

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• Circle the letter that answers the question. What
  is the displacement of a cyclist who travels 1
  mile north, then 1 mile east, and finally 1 mile
  south?
• a. 3 miles east b. 1 mile north
• c. 3 miles south d. 1 mile east

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• Circle the letter that answers the question. What
  is the displacement of a cyclist who travels 1
  mile north, then 1 mile east, and finally 1 mile
  south?
• a. 3 miles east b. 1 mile north
• c. 3 miles south d. 1 mile east

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