Physics 107 Ideas of Modern Physics

Transcription

1 Physics 107 Ideas of Modern Physics Course home page: Syllabus: Course info:

2 Your job Read the lecture notes, consult textbook for details Hobson, Physics Concepts and Connections Participate in the lectures Interrupt me any time you have a question, idea, Participate in the discussion sections (optional) Starting next week Do the homework Assigned Wednesdays, due the following Wednesday Write an essay or give a presentation See the link on the course home page Take the exams Three exams (incl. final); Two best of three counted

3 Grading Two best of three exams: 25%+25% Homework: 25% Essay or presentation: 25%

4 Topics of the course Ideas that revolutionized physics The big questions in physics today The impact of physics on our life Goethe s Faust makes a pact with the devil to find out whatever holds the world together at its inner core : "was die Welt im Innersten zusammenhält" Critical judgment Back-of-the-envelope calculations Separating science from religion, philosophy, myth,

5 From the small Nanoscience Manipulating single atoms to create quantum waves to the large: Cosmology How did the Universe begin? How will it end?

6 The top 11 questions in astrophysics What Is Dark Matter? What Is the Nature of Dark Energy? How Did the Universe Begin? Did Einstein Have the Last Word on Gravity? What Are the Masses of the Neutrinos? How Do Cosmic Accelerators Work? Are Protons Unstable? What Are the New States of Matter at Exceedingly High Density? Are There Additional Space-Time Dimensions? How Were the Elements from Iron to Uranium Made? Is a New Theory of Matter and Light Needed at the Highest Energies?

7 The Physics of Weather

8 Storms Where do storms get their energy from? From water vapor. It takes a lot of energy to vaporize liquid water on a stove. This energy is released when water vapor is converted back to liquid water in clouds (which consist of little droplets). A large storm sweeps up water vapor from vast stretches of warm ocean, particularly in the tropics. With global warming the oceans get warmer. More water evaporates and produces more fuel for storms.

9 Hurricanes 1) Moist air (orange) is pulled into the low pressure region at the center of a hurricane (the eye). 2) It rises at the eyewall and forms clouds. Condensing water releases energy, which gets converted into wind energy. 3) The air is expelled at the top forming thin clouds (blue).

10 Formation of spirals in cyclones (hurricanes, low pressure systems) Satellite photo: A low pressure system over Iceland forms a spiral with counter-clockwise rotation. So does a hurricane. Why? Low pressure pulls the air towards the center of a storm (blue arrows). The rotation of the Earth creates the Coriolis force (red arrows). It deflects the wind towards the right in the Northern Hemisphere. The two forces become balanced when the air moves in counter-clockwise fashion (opposite red and blue arrows). Low For details, download Cyclone from the Lecture Notes.

11 Passage of a low pressure system H Cold front Warm front Madison Typically, low pressure systems move from West to East at latitudes north of Madison. As a system moves through, the wind rotates from South to West and North, following the counter-clockwise rotation around the low pressure.

12 Global Wind Patterns Low High High Westerlies Trade Winds Low High Low

13 The Trade Winds N Low Low Low Low Low Low Low Hot air rises at the Equator and creates a ring of low pressure. Air is pulled towards the low pressure (blue arrows). The Coriolis force deflects the wind towards the West (red arrows) until the two forces balance each other ( red and blue arrows opposite). S

14 Hurricane Tracks Hurricanes start near Africa, carried west by the trade winds. They drift north and catch the Westerlies, which carry them back east. That s how Columbus sailed to America and back.

15 Summary A variety of weather patterns can be explained by a combination of the Coriolis force and the force pulling air towards low pressure. The spiral pattern of cyclones (Hurricanes and low pressure systems) is created by a central disk of low pressure. The global wind pattern is generated by a ring of low pressure around the Equator, where hot air rises. The Coriolis force is caused by the rotation of the Earth. It deflects winds to the right in the Northern Hemisphere (to the left in the Southern Hemisphere (mnemonic: southpaw = left-handed). Adding the pull towards low pressure to the Coriolis force causes the (counter-intuitive) counter-clockwise rotation of cyclones in the Northern Hemisphere.