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ENGI 1313 Mechanics I . Lecture 07: Vector Dot Product. Chapter 2 Objectives. to review concepts from linear algebra to sum forces, determine force resultants and resolve force components for 2D vectors using Parallelogram Law to express force and position in Cartesian vector form
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ENGI 1313 Mechanics I Lecture 07: Vector Dot Product
Chapter 2 Objectives • to review concepts from linear algebra • to sum forces, determine force resultants and resolve force components for 2D vectors using Parallelogram Law • to express force and position in Cartesian vector form • to examine the concept of dot product
Lecture 07 Objectives • to examine the concept of dot product
Overview of Dot Product • Definition • Laws of Operations • Commutative law • Scalar Multiplication • Distributive law
Overview of Dot Product (cont.) • Dot Product of Cartesian Vectors Go to zero
Application of Dot Product • Angle between two vectors • Cables forces and the pole? • • and ? Component magnitudes
If A||has + sense then same direction as u ^ Application of Dot Product (cont.) • Component magnitudeof A on a parallel or collinear linewith line aa • Recall Component A||
Application of Dot Product (cont.) • The vector A|| canbe determined by: Vector A|| Application of Dot Product for Component A|| Multiply by Unit Vector ûto obtain Vector A||
Application of Dot Product (cont.) • For force vector F at Point A: What is the component magnitudeparallel (|F1|) to the pipe (OA)?
Application of Dot Product (cont.) • For force vector F at Point A: what is the component magnitudeperpendicular (F2) to the pipe (OA)? • Method 1 • Method 2
Comprehension Quiz 7-01 • The dot product of two vectors results in a _________ quantity. • A) scalar • B) vector • C) complex number • D) unit vector • Answer: A
A Example Problem 7-01 • For the Cartesian force vector, find the angle between the force vector and the pole, and the magnitude of the projection of the force along the pole OA
A Example Problem 7-01 (cont.) • Position vector rOA • Magnitude of |rOA| • Magnitude of |F|
A Example Problem 7-01 (cont.) • Find the angle between rOA and F
A Example Problem 7-01 (cont.) • Find magnitude of the projection of the force F along the pole OA
Comprehension Quiz 7-02 • If the dot product of two non-zero vectors is 0, then the two vectors must be ______ to each other. • A) parallel (pointing in the same direction) • B) parallel (pointing in the opposite direction) • C) perpendicular • D) cannot be determined. • Answer: C
Comprehension Quiz 7-03 • The Dot product can be used to find all of the following except ____ • A) sum of two vectors • B) angle between two vectors • C) vector component parallel to a line • D) vector component perpendicular to a line • Answer: A
Comprehension Quiz 7-04 • Find the dot product (PQ) for • A) -12 m • B) 12 m • C) 12 m2 • D) -12 m2 • E) 10 m2 • Answer: C
Classification of Textbook Problems Hibbeler (2007)
References • Hibbeler (2007) • http://wps.prenhall.com/esm_hibbeler_engmech_1