welcome to physics 100 !!!! dr. gregory g. wood fall 2005

Welcome to Physics 100 !!!!

Dr. Gregory G. Wood

Fall 2005

A bit about me…. Just joined CSUCI Married to Dr. Tabitha Swan-Wood

Expecting a baby girl Jan. 15, 2005

Quiz

1) What is your name?

2) What is your major?

3) What is the email address you would like correspondence about this course sent to?

4) Why are you taking physics? (Try to put something more than “because I have to…”)

5) Tell me a bit about yourself.

What is Physics?

Broadly defined: A scientific method used to explain physical phenomena in the universe using the tools of mathematics.

Examples of Physics…

Classical Mechanics: Motion of the planets 1-D Atomic Chain Transverse Modes-Java Applet

Examples of Physics…

Light & Waves: Rainbows & Prisms

Ultra-Sounds

Examples of Physics…

Light & Waves: Atomic Scale Imaging

Examples of Physics…

Quantum Mechanics & Solid State: Transistors and Solid Electronics

Physics Permeates Your Life

TV Radio Computers Automobiles Plasma Screens Medical Instruments: MRI, Ultrasound,

X-rays,…

Chapter 1

Skim Chap. 1 and make sure you understand it.

Important prefixes:

Power Prefix Abbreviation

103 kilo k

10-2 centi c

10-3 milli m

10-6 micro

Chapter 1

Dimensional Analysis: Units must be equal on both sides of an

equation [units] = [units]

When adding or subtracting units must be equal [units] + [units]

Examples Yes: 5 m/s = 3 m/s + 2 m/s No: 5 m/s = 3 m/s2 + 2 m/s

Chapter 1

Scientific Notation 3,240 = 3.24 x 103

Converting Units To convert 23 seconds to units of hours:

23 sec x 1 min x 1 hour 60 sec 60 min

= 0.00639 hr = 6.39 x 10-3 hr

Chapter 1

How to Approach Physics Problems: Carefully read the problem Visualize the problem

Sketch a diagram of what’s happening

If complicated, try to separate the events Set-up the appropriate physics equations

Solve the equations Check your answer: units and magnitude Think about your answer

Chapter 1

A note on grading and partial credit Give a solid attempt at every problem Sketches will be worth something

Chapter 1 Distance vs. Displacement

Chapter 2 Position & Displacement…

Create an axis

0 m 6 mposition

At t=0sec Marm is at 0m and at t=3sec Marm is at 6m Total Displacement (6m-0m) = 6m Total Time (3sec-0sec) = 3sec

Chapter 2

0 m 6 mposition

At t=0sec Marm is at 0m and at t=3sec Marm is at 6m Total Displacement (6m-0m) = 6m Total Time (3sec-0sec) = 3sec

Average Speed Average Speed = Total Displacement

Average Velocity Equals average speed plus a direction Total Time

= 6m = 3 m3 sec sec

sec3 m

To the right

Chapter 2

Position vs. Time

Time [sec] Position [m]

0.8 1

2 2.2

4 3

6 3.5

Average Velocity: between t=0 sec and t=6 sec

Instantaneous Velocity: at t=6 sec

Slope of tangent line = instantaneous velocity

Chapter 2

Instantaneous Velocity Lim x

t0 t

tx

tx

Chapter 2

Average Acceleration

Instantaneous Acceleration

Units: v

if

ifave tt

vv

t

va

t

va

limt0

tm/s

sms2 =

Chapter 2 Negative Acceleration (Deceleration)

vf < vi becauseif

ifave tt

vv

t

va

v a +

Chapter 2

Motion under Constant Acceleration Useful Equations:

)122()(2

)112(2

1

)102()(2

1

)92()(2

1

)72(

020

2

200

00

0

0

xxavv

attvxx

tvvxx

vvv

atvv

av

Constant Accleration

)7.2(

lim

0

0

0

atvvt

vva

t

v

dt

dva

f

f

t

Aspen the dog starts at 2.0 m/s andaccelerates at 3.3 m/s2 for 1.1 s beforereaching top speed. What is her top speed?

Vf=2.0 m/s + 3.3 m/s2 x 1.1s = (2.0+3.63)m/s= 5.6 m/s (two sig figs).

v vs. t

A1=½ t * at

A2=v0t

at

t

v vs. t for Constant Acceleration

A1=½ t * at

A2=v0t

at

t

Distance = Area under v vs. t curve(because d = v*t)

d = A1 + A2

d = v0t + ½ t * at

x – x0 = v0t + ½ at2

x = x0 + v0t + ½ at2 (2-11)

How far?

atttvd2

10

Distance is the area under theVelocity vs. time graph thus:

D = area rectangle + area triangle

Area triangle = ½ base x height

)11.2(2

1 200 attvxx

Aspen the dog starts at 2.0 m/s andaccelerates at 3.3 m/s2 for 1.1 s beforereaching top speed. How far doesshe travel?

Position vs. Time Plots

200 2

1attvxx

Constant VelocityConstant Acceleration

Constant Deceleration

a = b + ct + dt2

a = b + ct – dt2

Upward Parabola

Downward ParabolaLarger slope equals larger velocity

Without time information…

)11.2(2

1 200 attvxx

)7.2(0 atvv f

Solve (2.7) for time and substitute into (2.11) and you will find:

)12.2()(2 020

2 xxavv f

Aspen goes from 2.0 m/s to 5.6 m/s over a distance of 4.2 m,find acceleration.

Chapter 2

Example 1 (prob. #12) It was a dark and stormy night, when

suddenly you saw a flash of lightening. Three-and-a-half seconds later you heard the thunder. Given that the speed of sound in air is about 340 m/s, how far away was the lightening bolt?

Chapter 2

Example 2 (prob. #40) When you see a traffic light turn red you

apply the brakes until you come to a sop. If your initial speed was 12 m/s, and you were heading due west, what was your average velocity during braking? Assume constant velocity.

Chapter 2

Example 3 (prob. #100) You drop a ski glove from a height h onto

fresh snow, and it sinks to a depth d before coming to rest. (a) In terms of g and h, what is the speed of the glove when it reaches the snow? (b) What are the magnitude and direction of the glove’s acceleration as it moves through the snow, assuming it to be constant? Give your answer in terms of g, h, and d.

Lab One Activity: Measure a

4-setups: measure time and distance Assume constant acceleration Each group uses different angle of

incline Use a variety of distances – average

all a values Rest login to MP website/homework