Dr. Tyler NordgrenPhysics 231: General Physics I

Dr. Tyler NordgrenPhysics 231: General Physics I

Today• 1st-Day-of-Class logistics• 1st-chapter-of-the –book big picture / stage setting• vector refresher

Motion is neither created nor destroyed, but transferred via

interactions.

Intro to Course

oThis Semester: Modern Mechanicso Mechanics = Kinematics (motion) & Dynamics (interaction)

o Fundamental Principle of Mechanicso “Modern”o Simulations

o Level o Math

o Algebra & basic Trig o Calculus

o Slow starto Physics

o No Previous requiredo Deeper than High School

•AlternativePhys 220-221

oThe DifferenceoTime to decide.

oSpecial NeedsoRoll Call

Syllabus• Office Hours: Monday 1:00pm-3:00pm, Wednesday 2:00pm-4:00pm• Course Components

Reading Text

If you don’t have it Assignments

oReading Exerciseso WebAssign

www.webassign.net. User name: first_last, Password: Appleton Free Trial Demonstration First Assignment

(Weekly) HomeworkExploring Physics

First OneLab – bring laptop if you have oneQuizesExams

Schedule

Misc.oWeb-site – it’s all thereoSupplies

Pencil Paper / notebook Calculator

oWorking TogetheroCheating

Today’s Reading1.1 Kinds of Matter1.2 Detecting Interactions1.3 Newton’s First Law of Motion1.4 Describing the 3D World: Vectors1.5 SI Units

Q1.2.a: Moving objects left the traces shown at left. The dots were laid down at equal time intervals. Which objects did NOT interact with another object somewhere?1. A2. B3. C4. D5. A and D6. A and B7. A, B, and D

Q1.2.bWhich of the following can NOT be true for an object moving in a straight line at a constant speed?

1. Nothing is interacting with the object (it is in interstellar space, far from all other objects).

2. The object is experiencing a net interaction.

3. The object is experiencing multiple interactions, and these interactions add up to zero.

4. The object has no net interaction with the rest of the world.

Newton’s First Law – “An object moves in a straight line and at a constant speed except to the extent that it interacts with other objects.”

Forces – How are you here?

Forces between atoms.Forces between atoms and Earth.Forces between Earth and Sun.Forces between Sun and Galaxy.Forces between Galaxy and ?

Practice with Vectors

Practice with Vectors

A

A’s Position: <3,6,0>units (relative to the origin)

Component Representation: zyx rrrr ,,

Practice with Vectors

A

A’s Position: <3,6,0>units

B

B’s Position: <____,_____,0>units

Component Representation: zyx rrrr ,,

Practice with Vectors

A

A’s Position: <3,6,0>units

B

B’s Position: <-7,-2,0>units

Graphical / Arrow Representation:

Ar

Br

Practice with Vectors

A

B

Subtraction:

Ar

Br

ABAB rrr

ABr

units

unitsrrrrrrrrr zAzByAyBxAxBABAB

0,8,10

00,62,37,, ......

May not be obvious.Imagine walking from Origin to A then to B.A friend at the Origin meets you at B.In the end you are both the same distance from the Origin.So:O A B = O BrA + rBA = rB

OR

rBA = rB - rA

Practice with Vectors

A

B

Subtraction:

Ar

Br

ABAB rrr

ABr

units

unitsrrrrrrrrr zAzByAyBxAxBABAB

0,8,10

00,62,37,, ......

Practice with Vectors

A

B

Subtraction:

Ar

Br

ABAB rrr

ABr

units

unitsrrrrrrrrr zAzByAyBxAxBABAB

0,8,10

00,62,37,, ......

Q1.5.bWhat is < 10, 20, −15 > − < 5, −8, 7 > ?

1) 192) 38.73) < 15, 12, 8 >4) < 5, 28, −22 >5) < 5, 12, −8 >

Practice with Vectors

A

B

Magnitude: ABr

ABr

Practice with Vectors

A

B

Magnitude: ABr

ABr

xABr .

yABr .

Pythagorean's Theorem:

unitsunitsr

rrrr

AB

zAByABxABAB

641000810222

2

.

2

.

2

.

Practice with Vectors

A

B

Magnitude: ABr

ABr

xABr .

yABr .

Pythagorean's Theorem:

unitsunitsunitsr

rrrr

AB

zAByABxABAB

8.12641000810222

2

.

2

.

2

.

1. 5.482. 6.163. 6.004. 30.005. 38.00

Q1.5.d What is the magnitude of the vector < 3, 5, −2 > in some arbitrary units?

Practice with Vectors

A

B

direction: ABr ˆ

ABr

0,625.0,78.08.12

0,8,10ˆ

units

units

r

rr

AB

ABAB

Practice with Vectors

A

B

direction: ABr ˆ

ABr

0,625.0,78.08.12

0,8,10ˆ

units

units

r

rr

AB

ABAB

Practice with Vectors

A

B

direction: ABr ˆ

ABr

0,625.0,78.08.12

0,8,10ˆ

units

units

r

rr

AB

ABAB

ABr ˆ

a. < 3, 5, −2 >b. < 1, 1, −1 > c. < 0.49, 0.81, 0.32 >d. < 0.49, 0.81, −0.32 >e. < 0.3, 0.5, −0.2 >

Q1.5.eWhat is the unit vector in the direction of the vector < 3, 5, −2 > in some arbitrary units?

http://www.wired.com/2010/11/1110mars-climate-observer-report/

For next time.

• Buy the book.• Email if you won’t have it by Friday.• Sign in to WebAssign, Do RE1 tonight.• For Friday do RE2.• Labs begin THIS week: AHON 1101• Starting Friday, all lectures in AHON 116.