Physics 140 – Winter 2015Prof. Keith Riles

January 7

LIGO Hanford Observatory(Washington)

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Physics 140 is a calculus-based introductory course intended for • engineering students• potential majors in the natural sciences• students skilled in trigonometry, algebra & calculus

Physics 140 is generally not intended for • pre-medical / nursing students (see physics 135)• students looking only to satisfy Nat Sci distribution• students with no background in calculus

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Overarching goals for this course:

1. Gain solid grounding in Newtonian mechanics

This course is largely devoted to understanding motion:

• Kinematics – Description of motion

• Dynamics – Causes of (and constraints on) motion

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2. Gain reliable intuition

3. Learn to solve hard problems1. Analytically2. Via numerical modeling (programming)

We will study the motion of various objects:

• Idealized particles

We will study both translational dynamics and the rotational analog (which follows from the first)

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• Flexible, elastic bodies, e.g., waves on strings

• Rigid bodies, including their rotation

• Systems of particles, including fluids

Force Relative Strength

Distance Scale Manifestation

Strong 1 ~10-15 m Holds nuclei together

Electromagnetic ~10-2 Infinity Holds atoms (+people) together

Weak ~10-13 ~10-18 m Certain radioactivity

Gravitational ~10-43 Infinity Holds Earth / Galaxy together

Four Fundamental Forces of Nature

Two force types we encounter every day 6

Gravity is obvious

Electromagnetic force may seem surprising to you, but it helps to realize that the dominant force between atoms is electromagnetic

Pushing an object is fundamentally an electromagnetic act

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Gravity is intrinsically weaker at the microscopic level, but the mass of the entire Earth makes the total force large

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Examples of ForcesGravitational:

Force between masses M and m separated by distance r

Force on mass m near Earth’s surface

Electromagnetic:

Restoring spring force

Normal force (special case of restoring force)

Friction – dissipative (mechanical energy lost)

But it breaks down in these regimes:

• at very small (atomic) distances (quantum mechanics)

• at very high speeds (special relativity)

• under strong gravity (general relativity)

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We will study Newtonian Mechanics which works very well in most cases

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Physics is both:

A fundamental science to understand & explain the laws that govern the natural world

and…

A set of tools to apply in other science and engineering

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Fundamental Science

About 4/5 of all matter is “Dark”

The M81 galaxy spins too fast for its stars alone to hold it together

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Fundamental Science

Large Hadron Collider (Switzerland) The LHC accelerator at CERN may allow creation and discovery of the elementary particles that make up Dark Matter

(now that the elusive Higgs Boson has been nabbed)

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Fundamental Science

Tracking the orbits of stars near our galaxy’s center (Sagittarius A) reveals the presence of a different kind of dark matter – a supermassive Black Hole heavier than 3.7 million Suns!

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Fundamental Science

The spiraling collisions of smaller black holes and neutron stars should create (according to Einstein) ripples in space itself, known as Gravitational Waves.

LIGO Hanford Observatory(Washington)

I collaborate with other physicists on an experiment called LIGO to search for those waves with giant laser interferometers.

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Physics as a Tool – Medicine

Magnetic Resonance Imaging

Ultrasound Imaging

And of course, X-rays …

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Physics as a Tool – Technology

Solar Energy

Data Storage

Laser Fusion

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Physics as a Tool – Civil Engineering

Hoover Dam (1936) and its Bypass Bridge (2010)

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Physics as a Tool – Engineering

Temporary suspension bridge

Closing the gap

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Physics as a Tool – Engineering

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Physics as a Tool – Avoiding Mistakes

Gare Montparnasse – 1896

Tacoma Narrows Bridge – 1940

Course logistics

• Course web site: http://ctools.umich.edu• Textbook: Young & Freedman (13th ed)• Reading assignments – see CTools syllabus• Viewing – see CTools schedule page for youtube links• Slides shown in class placed in Ctools resources• Class participation via i>clickers• On-line homework via Mastering Physics (MaPhys) • Numerical modeling homework –using Python/VPython• Grade reports via Gradebook 2 system (see CTools link)• Exams: 3 midterms (1.5 hr) and one final (2 hr)

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What about grades?

You will receive an overall score S, derived from weighting the course elements (on a 0-100 scale) as follows:

S = 0.20 (Mastering Physics homework)

+ 0.10 (participation - iclicker)

+ 0.14 (numerical modeling homework)

+ 0.12 (exam 1) + 0.12 (exam 2) + 0.12 (exam 3)

+ 0.20 (final)

Letter grade determination:

Based on your overall score

A (85), B (75-85), C (60-75), D (45-60), E (<45)

Extra credit opportunities on some numerical modeling homeworks22

What you should do for Physics 140 now

• Read the contents of the PHYSICS 140 CTools site

http://ctools.umich.edu

• Sign up for a MaPhys account, begin first assignment

• Read Chapter 1 of Y&F

• Purchase and register i>clicker remote

• Download & install Python/Vpython on your laptop

(see instructions on the CTools site)

• Consider joining an SLC study group

• Registration opens Friday January 16 at noon.

• First group meetings on Sunday January 1823

How can I do well in this course?

Be observant

Think about physics - it’s all around you!

Be organized

Allocate time (10%?) for reading/ homework/ study group

Be active

Try several approaches to studying & problem solving,

work with your peers (e.g., SLC-led study group)

Join the Piazza discussion groups (on Ctools)

Be patient

If at first you don’t succeed…

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Class sessions• Except for today, classes will not be traditional lectures• Mini-lectures will be posted on youtube in advance of class • I will assume you have viewed those lectures• I will focus in class on problem solving via peer instruction

and on demonstrations to illustrate concepts• Feel free to e-mail me (kriles@umich.edu) questions you may

have after viewing videos

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Recent academic research (confirmed in U-M physics courses in recent years) has shown that active learning via working in groups to solve posed problems leads to deeper understanding – as measured via exam performance.

To ensure that you benefit from this instruction, you will be asked to answer questions in class via i>clickers…

Where are you from?

A. Ann ArborB. Michigan palm C. Michigan U.P.D. USA (outside MI)E. Outside USA

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Normally:• Right answer: 4 points• Wrong answer: 3 points*• No answer: 0 points

Let’s try an i>clicker question!

But everyone excused this week!

*No points for incorrect answers to pre-lecture video questions

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Another one:

You plan to pursue a career in...

A) Engineering

B) Physics or physical sciences (astronomy, geophysics, biophysics, etc)

C) Other natural sciences (chemistry, biology, etc)

D) Mathematics or computer science

E) Non-science

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And one more…

You are buying a tennis racket with tennis balls. The sales person tells you that together they cost $110, and that the racket costs $100 more than the balls.

How much do the tennis balls cost?

A. $110 B. $100 C. $10D. $5 E. $0

Numerical modeling homework & labs

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Numerical modeling (and programming) have become essential skills to many engineers and scientists

Example:• Tiger Woods can hit a golf ball hundreds of yards• According to standard textbook approximations, he can hit much farther• You will show the difference!

Numerical modeling goals for this course:• Solve realistic problems without relying on poor analytical approximations • Learn basic algorithms for modeling and assessing accuracy• Learn systematic comparison of analytical and numerical methods• Learn rudiments of computer programming (Python & Vpython)

Numerical modeling homework & labs

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Every Thursday we will meet in Angell Hall Auditorium D. Starting next week will be numerical modeling labs devoted to getting you started on the modeling homework due (usually) the following week (extensions given during exam weeks).

There will be ten computer labs during the semester to which you should bring a laptop pre-loaded with the Python and Vpython programming language packages (see Ctools sidebar for installation information).

Some assignments later in the semester will offer extra credit opportunity.

Please start the Vpython tutorials (CTools) before next week’s lab!

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Syllabus on Ctools (partial snapshot)

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Progression of course

Vectors1-D motion2-D & 3-D motionCircular & relative motionNewton’s Laws

Exam 1 on February 5 (chapters 1-5)

Tomorrow’s material

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Progression of course

Work and kinetic energyPotential energyMomentum & impulseCollisions & center of massRotational kinematicsRotational dynamics

Exam 2 on March 12 (chapters 6.1-10.2)

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Progression of course

Angular momentumEquilibriumFluid staticsFluid dynamicsGravitation

Exam 3 on April 9 (chapters 10.3-13.7)

OscillationsMechanical waves

Final exam on April 24 (chapters 1-15)

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This course is challenging!

Foundational course for your career

But it’s also important

Treat it as a serious investment with great future dividends

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Questions?