PHYS 1441 – Section 002 Lecture #7 Wednesday, Feb. 6, 2008 Dr. Jaehoon Yu • Motion in Two Dimension – Motion under constant acceleration – Vector recap – Projectile Motion – Maximum ranges and heights Wednesday, Feb. 6, 2008 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu 1 Announcements • 1st term exam on Wednesday, Feb. 20 – Time: 1 – 2:20pm – Place: SH103 – Covers: Appendices, CH 1 – what we learn till next Wednesday, Feb. 13 – Class on Monday, Feb. 18: Jason will be here to go over the any problems you would like to review • Colloquium – Today at 4pm in SH101, following the refreshment at 3:30pm in SH108 – Please be sure to sign in the sign-in sheet Wednesday, Feb. 6, 2008 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu 2 Wednesday, Feb. 6, 2008 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu 3 Kinematic Quantities in 1D and 2D Quantities Displacement Average Velocity 1 Dimension x x f xi vx x f xi x t t f ti Inst. Velocity x vx lim t 0 t Average Acc. v x v xf v xi ax t t f ti Inst. Acc. Wednesday, Feb. 6, 2008is What v x ax lim t 0 t 2 Dimension r r r r r r r r f r i v t t f ti r r r v lim t 0 t r r r r v v f vi a t t f ti r r v a lim t 0 t PHYS between 1441-002, Spring the difference 1D2008 and 2D quantities? Dr. Jaehoon Yu r r r f ri 4 Kinematic Equations v vo at x 1 2 vo v t v v 2ax 2 2 o x vot at 1 2 Wednesday, Feb. 6, 2008 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu 2 5 A Motion in 2 Dimension This is a motion that could be viewed as two motions combined into one. Wednesday, Feb. 6, 2008 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu 6 Motion in horizontal direction (x) vxo vx t vx vxo axt x v v 2a x x x vxot ax t 2 x 2 xo Wednesday, Feb. 6, 2008 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu 1 2 1 2 2 7 Motion in vertical direction (y) v y v yo a y t y 1 2 v yo vy t v v 2ay y 2 y 2 yo y vyot ayt 1 2 Wednesday, Feb. 6, 2008 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu 2 8 A Motion in 2 Dimension Imagine you add the two 1 dimensional motions on the left. It would make up a one 2 dimensional motion on the right. Wednesday, Feb. 6, 2008 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu 9 Kinematic Equations in 2-Dim x-component y-component vx vxo axt v y v yo a y t x 1 2 vxo vx t 2 y 2 xo x vxot ax t 1 2 Wednesday, Feb. 6, 2008 v yo vy t v v 2ay y v v 2a x x 2 x y 1 2 2 2 yo y vyot ayt PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu 1 2 2 10 Coordinate Systems • They make it easy and consistent to express locations or positions • Two commonly used systems, depending on convenience, are – Cartesian (Rectangular) Coordinate System • Coordinates are expressed in (x,y) – Polar Coordinate System • Coordinates are expressed in distance from the origin ® and the angle measured from the x-axis, q (r,q) • Vectors become a lot easier to express and compute +y How are Cartesian and Polar coordinates related? y1 (x1,y1) =(r1,q1) r1 x1 r1 cos q1 r x12 y12 1 q1 O (0,0) Wednesday, Feb. 6, 2008 x1 +x y1 r1 sin q1 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu y1 tan q1 x1 y1 x 1 q1 tan 1 11 Example Cartesian Coordinate of a point in the xy plane are (x,y)= (-3.50,-2.50)m. Find the equivalent polar coordinates of this point. r y q qs (-3.50,-2.50)m 2 y2 3.50 2 2.50 2 18.5 4.30( m) x r x q 180 q s 2.50 5 3.50 7 tan q s 1 5 q s tan 35.5 7 o o o q 180 q s 180 35.5 216 Wednesday, Feb. 6, 2008 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu o 12 Properties of Vectors • Two vectors are the same if their sizes and the directions are the same, no matter where they are on a coordinate system!! Which ones are the same vectors? y D A=B=E=D F A Why aren’t the others? B x E Wednesday, Feb. 6, 2008 C PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu C: The same magnitude but opposite direction: C=-A:A negative vector F: The same direction but different magnitude 13 Vector Operations • Addition: – Triangular Method: One can add vectors by connecting the head of one vector to the tail of the other (head-to-tail) – Parallelogram method: Connect the tails of the two vectors and extend – Addition is commutative: Changing order of operation does not affect the results A+B=B+A, A+B+C+D+E=E+C+A+B+D A+B B A • A = B A+B OR A+B B A Subtraction: – The same as adding a negative vector:A - B = A + (-B) A A-B • -B Since subtraction is the equivalent to adding a negative vector, subtraction is also commutative!!! Multiplication by a scalar is increasing the magnitude A, B=2A Wednesday, Feb. 6, 2008 B 2A A PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu B=2A 14 Example for Vector Addition A car travels 20.0km due north followed by 35.0km in a direction 60.0o west of north. Find the magnitude and direction of resultant displacement. r Bsin60oN B 60o Bcos60o r q 20 A 2 B sin q 2 A2 B 2 cos 2 q sin 2 q 2 AB cosq A2 B 2 2 AB cosq 20.02 35.02 2 20.0 35.0 cos 60 2325 48.2(km) E B sin 60 q tan 1 tan 1 35.0 sin 60 20.0 35.0 cos 60 30.3 38.9 to W wrt N 37.5 tan 1 Wednesday, Feb. 6, 2008 A B cosq A B cos 60 PHYS 1441-002, Spring 2008 Dr. Jaehoon Yu Find other ways to solve this problem… 15