10.2 Vectors in the Plane

Warning: Only some of this is review.

Quantities that we measure that have magnitude but not direction are called scalars. Quantities such as force, displacement or velocity that have direction as well as magnitude are represented by directed line segments. A B initial point terminal point The length is

A B initial point terminal point A vector is represented by a directed line segment. Vectors are equal if they have the same length and direction (same slope).

A vector is in standard position if the initial point is at the origin. x y The component form of this vector is:

A vector is in standard position if the initial point is at the origin. x y The component form of this vector is: The magnitude (length) ofis:

P Q (-3,4) (-5,2) The component form of is: v (-2,-2)

If Then v is a unit vector. is the zero vector and has no direction.

Vector Operations: (Add the components.) (Subtract the components.)

Vector Operations: Scalar Multiplication: Negative (opposite):

v v u u u+v u + v is the resultant vector. (Parallelogram law of addition)

The angle between two vectors is given by: This comes from the law of cosines.

The dot product (also called inner product) is defined as: Read “u dot v” Example:

The dot product (also called inner product) is defined as: This could be substituted in the formula for the angle between vectors (or solved for theta) to give:

Find the angle between vectors u and v : Example:

Application: Example 7 A Boeing 727 airplane, flying due east at 500mph in still air, encounters a 70-mph tail wind acting in the direction of 60 o north of east. The airplane holds its compass heading due east but, because of the wind, acquires a new ground speed and direction. What are they? N E

Application: Example 7 A Boeing 727 airplane, flying due east at 500 mph in still air, encounters a 70-mph tail wind acting in the direction of 60 o north of east. The airplane holds its compass heading due east but, because of the wind, acquires a new ground speed and direction. What are they? N E u

Application: Example 7 A Boeing 727 airplane, flying due east at 500mph in still air, encounters a 70-mph tail wind acting in the direction of 60 o north of east. The airplane holds its compass heading due east but, because of the wind, acquires a new ground speed and direction. What are they? N E v u 60 o

Application: Example 7 A Boeing 727 airplane, flying due east at 500mph in still air, encounters a 70-mph tail wind acting in the direction of 60 o north of east. The airplane holds its compass heading due east but, because of the wind, acquires a new ground speed and direction. What are they? N E v u We need to find the magnitude and direction of the resultant vector u + v. u+v

N E v u The component forms of u and v are: u+v Therefore: and:

N E The new ground speed of the airplane is about mph, and its new direction is about 6.5 o north of east o 

Studying Planar Motion A particle moves in the plane with position vector r(t) =. Find the velocity and acceleration vectors and determine the path of the particle.

Studying Planar Motion A particle moves in the plane with position vector r(t) =. Find the velocity and acceleration vectors and determine the path of the particle. Velocity v(t) = Acceleration a(t) = The path of the particle is found by graphing the curve and using path.

Doing Calculus Componentwise A particle moves in the plane so that its position at any time t ≥ 0 is given by (sin t, t 2 /2). a)Find the position vector of the particle at time t b)Find the velocity vector of the particle at time t c)Find the acceleration of the particle at time t. d)Describe the position and motion of the particle at time t= 6.

Doing Calculus Componentwise A particle moves in the plane so that its position at any time t ≥ 0 is given by (sin t, t 2 /2). a)Find the position vector of the particle at time t. b) Find the velocity vector of the particle at time t. c)Find the acceleration of the particle at time t. d)Describe the position and motion of the particle at time t= 6. The position vector, which has the same components as the position point is. Differentiate each component of the velocity vector to get. Differentiate each component of the acceleration vector to get. The particle is at the point (sin 6, 18) with velocity and acceleration.

Any vector can be written as a linear combination of two standard unit vectors. The vector v is a linear combination of the vectors i and j. The scalar a is the horizontal component of v and the scalar b is the vertical component of v.

We can describe the position of a moving particle by a vector, r ( t ). If we separate r ( t ) into horizontal and vertical components, we can express r ( t ) as a linear combination of standard unit vectors i and j.

In three dimensions the component form becomes:

Graph on the TI-89 using the parametric mode. MODE Graph…….2 ENTER Y= ENTER WINDOW GRAPH

Graph on the TI-89 using the parametric mode. MODE Graph…….2 ENTER Y= ENTER WINDOW GRAPH

Most of the rules for the calculus of vectors are the same as we have used, except: “Absolute value” means “distance from the origin” so we must use the Pythagorean theorem.

Example 5: a) Find the velocity and acceleration vectors. b) Find the velocity, acceleration, speed and direction of motion at.

Example 5: b) Find the velocity, acceleration, speed and direction of motion at. velocity: acceleration:

Example 5: b) Find the velocity, acceleration, speed and direction of motion at. speed: direction:

Example 6: a) Write the equation of the tangent where. At : position: slope: tangent:

The horizontal component of the velocity is. Example 6: b) Find the coordinates of each point on the path where the horizontal component of the velocity is 0. 