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**Starter If the height is 10m and the angle is 30 degrees,**

how long is the shadow? h/s = tanq, so s =h/tanq = 10/tan30 = 17.3m

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**Vectors and Vector Addition**

1. Characteristics of Vectors 2. Multiplying a vector by a scalar 3. Adding Vectors Graphically 4. Adding Vectors using Components

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What is a vector? A vector is a mathematical quantity with two characteristics: 1. Magnitude or Length 2. Direction ( usually an angle)

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Vectors vs. Scalars A vector has a magnitude and direction. Examples: velocity, acceleration, force, torque, etc.

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Vectors vs. Scalars A scalar is just a number. Examples: mass, volume, time, temperature, etc.

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**A vector is represented as a ray, or an arrow.**

The terminal end or head V The initial end or tail

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**Picture of a Vector Named A**

Magnitude of A A = 10 Direction of A q = 30 degrees

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**The Polar Angle for a Vector**

Start at the positive x-axis and rotate counter-clockwise until you reach the vector. That’s how you find the polar angle.

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**Two vectors A and B are equal if they have the same magnitude and direction.**

This property allows us to move vectors around on our paper/blackboard without changing their properties.

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**A = -B says that vectors A and B are anti-parallel**

A = -B says that vectors A and B are anti-parallel. They have same size but the opposite direction. A = -B also implies B = -A B A

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**Graphical Addition of Vectors ( Head –to Tail Addition )**

To find C = A + B : 1st Put the tail of B on the head of A. 2nd Draw the sum vector with its tail on the tail of A, and its head on the head of B. Example: If C = A+B, draw C. Here’s Vector C

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**Graphical Addition of Vectors ( Head –to Tail Addition )**

To find C = A - B : 1st Put the tail of -B on the head of A. 2nd Draw the sum vector with its tail on the tail of A, and its head on the head of -B. Example: If C = A-B, draw C. Here’s Vector C = A - B

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**Addition of Many Vectors**

B B D C C R D Add A,B,C, and D R = A + B + C + D

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**Multiplication of a Vector by a Number.**

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**Vector Addition by Components (Do the math)**

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**A vector A in the x-y plane can be represented by its perpendicular components called Ax and Ay.**

Components AX and AY can be positive, negative, or zero. The quadrant that vector A lies in dictates the sign of the components. Components are scalars. A AY x AX

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When the magnitude of vector A is given and its direction specified then its components can be computed easily y AX = Acosq A AY AY = Asinq x AX You must use the polar angle in these formulas.

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**Example: Find the x and y components of the vector shown if A = 10 and q = 225 degrees.**

AX = Acosq = 10 cos(225) = Ay = Asinq = 10 sin(225) A = (-7.07, -7.07)

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**The magnitude and polar angle vector can be found by knowing its components**

= tan-1(AY/AX) + C

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**Example: Find A, and q if A = ( -7.07, -7.07)**

= 10 = tan-1(AY/AX) + C = tan-1(-7.07/-7.07) + 180 = 225 degrees

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**Example: Find A, and q if A = ( 5.00, -4.00)**

= 6.40 = tan-1(AY/AX) + C = tan-1(-4.00/5.00) + 360 = 321 degrees

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**A vector can be represented by its magnitude and angle,**

or its x and y components. You can go back and forth’ from each representation with these formulas: If you know Ax and Ay you can get A and q with: If you know A and q, you can get Ax and Ay with: Ax = Acosq Ay = Asinq

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**Adding Vectors by Components**

If R = A + B Then Rx = Ax + Bx and Ry = Ay + By So to add vectors, find their components and add the like components.

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Example A = ( 3.00,2.00) and B = ( 0, 4.00) If R = A + B find the magnitude and direction of R. Solution: R = A + B = ( 3.00,2.00) + ( 0, 4.00), so R = ( 3.00, 6.00) Then R = ( )1/2 = 6.70 q = tan-1( 6/3) = 63.4o

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**Example If R = A + B find the magnitude and direction of R.**

1st: Find the components of A and B. Ax = 10cos 30 = 8.66 Ay = 10 sin30 = 5.00 Bx = 8cos 135 = -5.66 By = 8sin 135 = 5.66 2nd: Get Rx and Ry Rx = Ax + Bx = = 3.00 Ry = Ay + By = = 10.7 3rd: Get R and q : R = ( )1/2 = 11.1 q = tan-1 ( 10.7/3.00) = 74.3o

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**Summary If R = A + B Rx = Ax + Bx Ax = Acosq Ay = Asinq Ry = Ay + By**

If you know Ax and Ay you can get A and q with: If you know A and q, you can get Ax and Ay with: Ax = Acosq Ay = Asinq If R = A + B Rx = Ax + Bx Ry = Ay + By

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**Unit Vectors 𝑖 Examples: A = (3,-2,5) = 3i - 2j + 5k**

= ( 1, 0, 0) 𝑗 = ( 0, 1, 0 ) 𝑘 = ( 0, 0, 1) Examples: A = (3,-2,5) = 3i - 2j + 5k B = (3,0,5) = 3i + 5k

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**The Scalar or Dot Product**

Example: A = 3i +4j +5k B = 4i + 2j– 3k A.B = – 15 = 5

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**The Cross Product A x B = i( Ay Bz - Az By ) - j( Ax Bz - Az Bx )**

+ k( Ax By - Ay Bx )

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Example A = (3,0,2) B = (1,1,0) A X B = 𝒊 𝒋 𝒌 = i (0 -2) -j(0-2)+k(3-0) = -2i +2j +3k = (-2,2,3)

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**Integrals of Vectors 𝑨 𝑑𝑥=𝒊 𝐴 𝑥 dx + j 𝐴 𝑦 𝑑𝑥+𝒌 𝐴 𝑧 𝑑𝑥**

Example: If A = 3xi +5x2j , then find 𝑨 𝑑𝑥. 𝑨 𝑑𝑥=𝒊 3𝑥 𝑑𝑥 j 5𝑥2 𝑑𝑥= 3 2 𝑥2𝒊 𝑥3 𝒋

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**Derivatives of Vectors**

dA/dx = d (Ax, Ay, Az)/dx = (dAx/dx, dAy/dy, dAz/dz) Example: If A = 3ti - 5t2j , then find dA/dt. dA/dt = 3i -10tj

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EXIT If A = 6cos(3t)i +5cos(10t)j , then find 𝑨 𝑑𝑡.

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