SPH4C COLLEGE PHYSICS

Transcription

1 PH4C COLLEGE PHYIC MOTION & IT APPLICATION L (P.9-10 Physical Quantities Many things that we do can be measued and descibed: how much time we spend in school, the mass of the candy we buy, and the foce with which we thow a baseball. Time, mass, and foce ae examples of physical quantities. Physical quantities can be classified as eithe scala quantities o vecto quantities. A scala quantity has magnitude (size only. Fo example, a distance of 2.5 m, a speed of 23 m/s, a time inteval of 15 s. A vecto quantity has magnitude (size and also a diection (which ae often expessed in squae backets afte the measuement. Fo example, a displacement of 2.5 m[n], a velocity of 23 m/s[e], a foce of 15 N[]. eptembe 22, C1-1 CALAR Physical Quantities quantity that has only magnitude (size VECTOR quantity that has magnitude (size and diection NOTE! An aow above a vaiable indicates it is a vecto quantity. eptembe 22, C1-2 1

2 Physical Quantities 1. Indicate whethe each of the following is a vecto o scala quantity. (a 50 km/h (b 6 km/h[n] (c 2000 kg/m 3 (d 6 centuies (e 800 kg (f 1.0 kg/week (g 20 m/s[] (h 400 N[down] V V V eptembe 22, C1-3 Distance Distance is the total length of the path tavelled by an object in motion. Distance is a scala quantity epesented by the symbol d. Fo example, if you walk diectly fom home to the school in a staight line, you will tavel a distance of 500 m. If you walk fom the school to the libay and then etun home, you will tavel 1900 m (700 m m. eptembe 22, C1-4 Position Position is the distance and diection of an object fom a paticula efeence point. Position is a vecto quantity epesented by the symbol d. Fo example, if home is you efeence point, the position of the school is 500 m[e]. Note that the magnitude of the position is the same as the staight-line distance (500 m fom home to school, but the position also includes the diection (due east [E]. eptembe 22, C1-5 2

3 Once the position of an object has been descibed, you can descibe what happens to the object when it moves fom that position. This is displacement the change in an object s position. is epesented by the symbol ( means change in. eptembe 22, C1-6 As with any change, displacement can be calculated by subtacting the initial position vecto fom the final position vecto: = d final d initial eptembe 22, C1-7 And when an object changes its position moe than once (i.e., it expeiences two o moe displacements, the total displacement of the object can be calculated by adding the displacements using the following: dt = eptembe 22, C1-8 3

4 Fo example, if you walk diectly fom home to school you displacement is 500 m[e] (500 m[e] 0. If you then walk fom the school to the libay and then etun home, you total displacement will be 0 m (500 m[e] m[e] m[w]. Recall that displacement is the change in position. eptembe 22, C1-9 DITANCE(d total length of the path tavelled by an object in motion POITION( d distance and diection of an object fom a paticula efeence point DIPLACEMENT( change in the position of an object NOTE! The I unit fo distance, position, and displacement is the mete (m. eptembe 22, C1-10 DIPLACEMENT( whee = d d d d d f i f i is the displacement is the final position is the initial position TOTAL DIPLACEMENT( whee = T 1 2 T +... is total displacement is displacement #1 is displacement #2 NOTE! Î A common tem fo total displacement isesultantdisplacement. Ï Fo convenience, the aows in the fomulas above ae often dopped. d T eptembe 22, C1-11 4

5 2. What is you (i distance and (ii displacement if you: (a walk fom home to the libay and then back home? (a d = 2400 m; d = 0 m eptembe 22, C What is you (i distance and (ii displacement if you: (b walk fom the school to home and then to the libay? (b d = 1700 m; d = 700 m[e] eptembe 22, C What is you (i distance and (ii displacement if you: (c walk fom home to the school and then to the mall? (c d = 2000 m; d = 1000 m[w] eptembe 22, C1-14 5

6 3. A dog, pactising fo he agility competition, leaves he taine and uns 80 m due west to pick up a ball. he then caies the ball 27 m due east and dops it into a bucket. What is the dog s total displacement? d = 53 m[w] eptembe 22, C A ca changes its position fom a position 52 km[w] of home to a position 139 km[e] of home. What is the ca s displacement? d = 191 m[e] eptembe 22, C1-16 TEXTBOOK P.10 Q.5 U Check You Leaning eptembe 22, C1-17 6