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Unit -2 Distance vs. Displacement ... Value is always positive. Examples: distance, mass, temperature, time • Vector is a quantity that has direction. Value can be positive or negative.

Oct 24, 2020

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  • Name: -----------

    Unit -2

    Date: _ 10/3 __ Period: ------

    Distance vs. Displacement

    Essential Questions:

    • Why do we need 2 concepts for "how far" - distance vs.

    displacement?

    • How do we "measure" motion to communicate about it2

    Questi-ons we ask about motion

    • Where did the object start moving?

    • When did the object start moving?

    • How far did the object travel?

    • How fast was the object moving?

    • In what direction was the object moving?

    ~ Was the object speeding up or slowing down?

    The motion equations help to answer these' questions & make

    predictions about motion

    Formulas d

    Average Speed = .6.t

    !'iv Average Accderation = !'it

    Average Velocity = ~" - et

    vi + vf Average Velocity = ~-~

    2

    r - , ---,.Slide 2

    1 ~·

  • O_bjectives

    .. Explain the Greek symbol "delta" or~ This symbol appears a lot in physics and mathl

    • Define dist~nce

    • Define-displacement

    • Explain the difference between a scalar vs. v~ctor - which is-distance and which is displacement-'?

    Review: What is Hposition"?

    " Position or "x" is the location of the object on a coordinate systems ( or "number line").

    Os ls 2s

    0 Question: What is th~osition of the runner at.Os? Vm

    ., Question: What is the position of the runner at 2s?

    S-0/Yl

    sliae3

    Slide4

    2 ~·

  • What is "delta" or~?

    " ~ means '-'subtraction"

    • What are you subtracting? - -It depeuds .Qn the variable after~: _

    Formulas d

    Average Speed= Lit

    c'.', v A1,erage Acceleration = .:"It

    A v·1· L'i.X , 1-..vernge e oc1ty = L'i..t

    ~t means "subtract two time ·instants"

    Llx means "subtract two positions"

    ~v means "subtract two velocities"

    v- = v-+ ~ t t ' -

    Ayerage Velocity = V; + ""ir 2

    Slide 5

    A Tens you to subtract "initial" and ''finarJ values· 0 ~ means subtraction of

    "end value" - "start value"

    .. "end value" is called "final" or "f' e.g., x1 means "final position"

    " "start value" is called "initial" or "i" e.g. , xi means "initial position"

    Note: Initial means "start" NOT your name initials!

    Slide6

    3

  • ~ Tells you to subtract Hinitial" and Hfina!" vaJues

    • !J.. means subtraction of "initial value" - "final "9ffle"

    Today we will focus on 6.x

    • What values are you subtracting? It depends on the variable after ~:

    .At means "subtract two time instants"

    !J..x means "subtract two positions"

    .ti v means "subtract two velocities"

    Distance vs. Disp~acement

    .. Distance is the total length of your actual path Symbol: "d"

    ., Displacement is the straight path from start to finish Symbol: "!J..x" Math definition: 11,1: = x 1 - xi Conceptual Example:

    d is the actual path you took.

    L1x is the displacement - straight path from initial position to final position

    Slide 7

    Slide8

    4

  • Practice 1

    Frank walks from x1 to x2

    a)What is the distanced he travels? __ 1/,____D;_.n-J------=---

    b) What is· his displacement fix? tix = x2 - x1 = -20m - (25"rrij

    ~ -45"m \

    clire,.of,

    ----t--f---+---t----i------il,llill--+---+--+-----!, ___ .....__, X (m) -20 -10 0 10 20

    Practice 2

    Frank then walks from x2 to x3.

    a)What is the distanced he travels? 25' rYJ b )What is his displacement ll.x?

    30

    Slide 9

    .6x = X3 - X2 = sty) - (- z o JY1) = s rvr -t -zo/11 = 25"" I">)

    ~-7 . ............. :....-----'~---'----r ..... ;,_=~-=-=~--===·==

    -- I I I I ' ---1 x(m) -20 -10 0 10 20 30

    Slide 10

    ~-tu~ (!)r"'

    a.n--J.oU41& ,-

    Di rco(\..o"' (/.1 1'? ~ n'#

    Ma~ '-fuOfl. (,.,d

    2S:P1

    5

  • Practice 3

    Consider Frank's total trip from x1 to x3.

    a)What is1he distanced hetra-vels? '/~I"? + 2 S-PJ b)What is his clisplacement Ax? ~ rO'>,

    ""ac X3 ~xi~ 5' WI - (2s /o/1) = i 3 D;r,) ,r.c; f'lvz.. /"Y7 Ct.~ ,· ~

    X2 X3 /

  • Practke 3

    Draw the displacement of Frank's total trip from x1 to x3 as an arrow that points from start to finish:

    X2 X3 LlXtrJr X1 ~ It

    ' - I I .. r ' -20 -10 0 10 20 30 All vectors are drawn as arrows to show the direction.

    Displacement is an example of a vector!

    Practice 3 - Ans'1ver

    1 X (m)

    Slide 13

    Draw the displacement of Frank's total trip from x 1 to x3 as an arrow that points from start to finish: }"\.. c. . ,;d ,..

    CX j,-~ °"'t:,~ ~~ ,rivf:/' I __ _ X2 · X3 -20 m X 1 ..,_ ,;

    ,,,. "' ~"""""-===-==--"""""=a"""""' _______ """

    ----i---+-+----+----+-----ii,ffl-. --+-1-----+--l,~-. .-+I X (m) -20 -10 0 10 20 30

    Displacement is an example of a vector!

    Every kind of vector has a magnitude (how much) and direction (where):

    Example: -20 m is a displacement with a magnitude of 20m and a negative direction (to the left).

    Slide 14

    7

  • Exit Ticket

    Trish, Mike, and Juan-leave the park to go to a pizza shop. Trish takes path A, J~n takes path B, and ~ takes path C. Mi)G(._

    Jua:4\

    1. Who travels the longest distanced? _A _____ _ 2. Who has the largest displacement Ill..? SQft-1

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