Vector Quantities

1. Vector Quantities • We will concern ourselves with two measurable quantities: • Scalar quantities: physical quantities expressed in terms of a magnitude only. Scalar quantities consist of a number and a unit. Example: 100 m/s (no direction).

3. Vector Quantities • Vector quantities: quantities that are described by a magnitude and a direction. Vector quantities consist of a number, a unit, and a direction (basically, a scalar quantity with the direction indicated). Example: if east is considered to be positive, then west is negative, so the vector can described as 100 m/s, east or +100 m/s; 80 m/s, west or -80 m/s.

5. Vector Quantities • Vectors are represented by an arrow (). The tail of the arrow will always be placed at the point of origin for the measurement of the desired quantity. • The length of the arrow indicates the magnitude of the vector. • The orientation of the arrow indicates the direction.

7. Vector Resolution • Resultant: is the single vector that produces the same result as the combination of the separate vectors. Each separate vector is called a component vector. • We will examine the impact of all vector quantities acting upon an object as if all the vectors originate at a single point.

10. Vector Addition • When two or more vectors act at the same point in the same direction (in other words, the angle between each of the vectors is 0), the resultant is determined by adding all the component vectors together. • The direction of the resultant vector is in the direction of the component vectors.

11. If you walk 5 m to the right, stop, and then walk 3 m to the right, the total displacement is: 5 m + 3 m = 8 m. The 5 m vector and the 3 m vector are the component vectors. Resultant displacement = 8 m to the right Properties of Vectors (HRW) Vector Addition

12. Vector Subtraction • When two vectors act at the same point, but in opposite directions (the angle between each vector is 180), the resultant is equal to the difference between the two vector quantities (subtract). • The direction of the resultant is in the direction of the component vector with the largest magnitude.

13. If you walk 5 m to the right, stop, and then walk 3 m to the left, the total displacement is: 5 m – 3 m = 2 m The 5 m vector and the 3 m vector are the component vectors. Resultant displacement = 2 m to the right. Subtraction of Vectors (HRW) Vector Subtraction

14. When two or more vectors act at the same time (concurrently) on the same point, the resultant can be determined by placing the vectors head to tail. The tail of the first vector (A) will begin at the origin and the tail of the next component vector (B) is placed at the head of the vector A. Head to Tail Method

15. The tail of vector C is placed at the head of vector B. Each component vector is drawn with the correct orientation. The order in which the vectors are drawn does not matter as long as the magnitude and direction of each vector is maintained when drawn. Head to Tail Method

16. The resultant vector R would be the vector beginning at the origin and extending in a straight line to the head of the last vector. The determination of the magnitude will involve use of the Pythagorean theorem or the law of cosines. Head to Tail Method

18. Head to Tail Method • The direction of the resultant can be determined by resolving the resultant vector into x (horizontal) and y (vertical) components and using a trig function (sin, cos, or tan). • This will be described later. • Graphical Addition of Vectors & Adding Vectors Algebraically (HRW)

19. Example: move 5 m along the x-axis and then move 8 m up the y-axis. Place the origin of a coordinate system at the point where the motion begins or where the force is applied; you will start at (0,0) on the coordinate system. For Vector Problems Involving Right Angles

20. For Vector Problems Involving Right Angles • Tail of the 5 m vector goes at the origin and the head points along the x-axis and would lie on 5 on the axis. • At the head of the 5 m vector, turn up and the tail of the 8 m vector will begin and the head points up the y-axis and would lie on 8 on the axis. • The head of the 8 m vector would lie on the point (5,8) on an x-y coordinate plane.

21. Resultant vector R begins at the origin (0,0) and ends at the head of the 8 m vector [at the point (8,5)]. The 5 m vector and the 8 m vector are the component vectors. For Vector Problems Involving Right Angles

22. The resultant R is the hypotenuse of a right triangle formed by the 5 m vector and the 8 m vector. Use the Pythagorean theorem to determine the magnitude of the resultant R: R2 = A2 + B2 R2 = (5 m)2 + (8 m)2 R2 = 89 m2; R = 9.43 m For Vector Problems Involving Right Angles

23. For Vector Problems Involving Right Angles • To determine the direction of the resultant vector: • Requires an angular measurement and a direction moved from a reference axis. Example: 40 above the x-axis. • Choose one of the two angles at the point of origin. The reference axis is the adjacent side of the selected angle.

24. Trig Functions Any one of the trig functions (sin, cos, or tan) can be used to find the direction of the resultant vector R. Be sure the calculator is in degree mode! For Vector Problems Involving Right Angles

26. For Vector Problems Involving Right Angles • Report the angle determined with the trig function and the direction moved from the reference axis. Example: • Use the inverse tan function (tan-1) to determine the angle q.

27. q = tan-1 1.6 q = 57.995o To get to the resultant, you must start at the x-axis and rotate 57.995o above the x-axis. The magnitude of the resultant is 9.43 m and the direction is 57.995o above the x-axis. For Vector Problems Involving Right Angles

28. X and Y Components of a Vector Vectors can be resolved (broken down) into a component that acts along the x-axis and a component that acts along the y-axis. The tail of the vector to be resolved is placed at the origin and drawn as indicated in the problem.

29. X and Y Components of a Vector Ex: the 50 m/s vector located 30° above the positive x-axis will be resolved into an x-component and a y-component.

30. X and Y Components of a Vector From the origin, draw a line along the x-axis to a point below the tip of the head of the vector (the arrow head). This is the x-component of the vector. From the origin, draw a line along the y-axis to a point adjacent to the tip of the head of the vector (the arrow head). This is the y-component of the vector.

31. X and Y Components of a Vector Construct a parallelogram (either a square or a rectangle). A parallelogram is used because the opposite sides of a parallelogram are equal in magnitude. You also have two right triangles which you can use to solve for the components. The 50 m/s the diagonal of the parallelogram and will be the hypotenuse for the right triangle you will use to determine the x-component and the y-component.

32. X and Y Components of a Vector The x-component is the adjacent side of the right triangle and you will use the cosine function to determine its magnitude.

33. X and Y Components of a Vector

34. X and Y Components of a Vector The y-component is the opposite side of the right triangle and you will use the sine function to determine its magnitude.

35. X and Y Components of a Vector

36. X and Y Components of a Vector Summarized

39. For problems involving multiple vectors: Rectangular Resolution Resolve each vector into an x-component and a y-component using the trig functions sine or cosine, whichever is appropriate. Be careful to denote the negative values for the x- and y-components, when appropriate. Add all the x-components together to get one resultant x-component vector. Add all the y-components together to get one resultant y-component vector.

40. For problems involving multiple vectors: Rectangular Resolution Use the Pythagorean theorem to determine the resultant vector. Use a trig function (sine, cosine, or tangent) to determine the angle of orientation for the resultant vector. Visit Adding Vectors Algebraically (HRW)

41. Example 3C, p. 95 Given two vectors: 25.5 km at 35° south of east 41 km at 65° north of east Draw the two vectors on the coordinate grid. The tail of the first vector goes at the origin.

42. Example 3C, p. 95 To draw 35° south of east: place the protractor on the origin with the 90° mark on the south axis and the 0° mark on the east axis. Measure 35° from the east axis toward the south axis. Draw the 25.5 km vector from the origin at 35°.

43. Example 3C, p. 95 Make the head of the 25.5 km vector the origin. From the head of the 25.5 km vector, draw the 41 km vector with its tail at the origin and measure the 65° angle from the horizontal axis. To draw 65° north of east: place the protractor on the origin with the 90° mark on the north axis and the 0° mark on the east axis. Measure 65° from the east axis toward the north axis. Draw the 41 km vector from the origin at 65°.

44. Example 3C, p. 95

45. Example 3C, p. 95 The resultant vector R is the vector that begins at the origin and ends at the head of the 41 km vector. Determine the x-component and the y-component for the two vectors.

46. Example 3C, p. 95

47. Example 3C, p. 95 25.5 km: x-component

48. Example 3C, p. 95 25.5 km: y-component

49. Example 3C, p. 95

50. Example 3C, p. 95 41 km: x-component