PHYS16 – Lecture 3

Physics of 1D MotionFriday, September 10, 2010

Looney Tunes

• Administration• Vectors• Review from last week• Key Concepts – Physics 1D motion• Displacement, Velocity, & Acceleration

Agenda

• Register Clickers• Textbook

– University Physics vol. 1 by Bauer & Westfall

• Connect Physics– http://connect.mcgraw-hill.com/class/a_carter_fall_2010

• Math Exam• Homework Assignments– On course website– On Connect website

Administration

Review from last week

• Significant figures– Every digit that has meaning (not trailing or leading zeros)– 0.00543 has 3 significant figures– When multiply/divide keep # of sig figs of number with lowest

amount of sig figs– When add/subtract keep # to the lowest decimal

• Scientific Notation– Way of expressing number with sig figs and order of magnitude– 12,300,000 is 1.23E7

• Units– Know prefixes – milli = 10^-3, kilo=10^3– Conversion

• If 1 M = 1 mol/L then 4.0 mol in 3.0 L is? 4.0 mol/3.0 L = 1.3 M • If 25.4 mm = 1 in then 3.2 in = mm? 3.2 in*25.4 mm/in= 81 mm

Vectors

• Vector vs. Scalar– Vector – quantity with both magnitude and direction– Scalar – quantity with just magnitude

• Which is a vector and which is a scalar?– 25 apples in a bucket (scalar)– Car coming at me at 100 mph (vector)– I live 6 miles from grandma (scalar)– Grandma’s house is 6 miles east of here (vector)

Vector

• Representation• Finding Vector components – Use Trig!!!

sin cos

arctan

),(

22

VVVV

V

V

VVV

VVV

yx

y

x

yx

yx

Math Review Questions 1

Let’s say we make a measurement of our position with 3 different GPS devices (GPS watch, GPS phone, and a car GPS) and we know that we are right next to the bank (red x). Which GPS is the most ACCURATE?

A.GPS watchB.GPS phoneC.Car GPS

BANKGROCERY

Math Review Questions 2

Let’s say we make a measurement of our position with 3 different GPS devices (GPS watch, GPS phone, and a car GPS) and we know that we are right next to the bank (red x). Which GPS is the most PRECISE?

A.GPS watchB.GPS phoneC.Car GPS

BANKGROCERY

Math Review Questions 3

A problem asks you to find the pressure (P) a piston exerts given a force (F) of 23.7 N and a length (l) and width (w) of the piston of 11 cm and 0.001 km, respectively. The equation that governs this is P=F/(lw). How many significant digits should you enter in your answer?

A. 1B. 2C. 3D. 4E. There is not enough information.

Math Review Questions 4

A problem asks you to find the pressure (P) a piston exerts given a force (F) of 23.7 lbs and a length (l) and width (w) of the piston of 11 in and 0.001 in, respectively. The equation that governs this is P=F/(lw). What are the units of pressure?

A.lbsB. inC. lbs/inD. lbs/(in^2)E. There is not enough information.

Math Review Questions 5

What is the value for V3?

A. (4,4)B. (-2,2)C. (2,-2)D. (3,3)E. (4,3)

V3=?V2= (1,3)

V1= (3,1)

Key Concepts: Physics 1D Motion

• Displacement, Velocity, & Acceleration– Know the definitions of these terms– Know how they are related

• Motion with Constant Acceleration– Solve the equations of Motion for constant accel.– Know the 5 kinematic equations– Use the kinematic equations to solve problems

Displacement

• Displacement vs. Distance– Displacement = final position – initial position with

both magnitude and direction– Distance = total position traversed from final

position to initial position, just magnitude

Velocity

• Velocity vs. Speed– Velocity – final position minus initial position

divided by time, both magnitude and direction– Speed – how fast you are going, just magnitude

60 mph

Acceleration

• Acceleration– Final velocity minus initial velocity divided by time,

both a magnitude and a direction– How much an object speeds up or slows down

http://physics247. com

Position graph where acceleration is not 0

Questions

• Can displacement be zero and distance be positive? (Yes)

• Can distance ever be negative? (No)• Can speed ever be negative? (No)• Can acceleration be negative? (Yes)• Can an object that is stopped at t=0 have a

positive acceleration? (Yes)• If an object is traveling at a constant velocity can

it have an acceleration? (No)

For Next Time…

• Online homework due Tuesday• Online lab homework due Wednesday• Online Math Exam due Sunday

• Get your clicker, text, connect access…