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# 23 Apr 21 Assorted Topics, Mechanics Intro Actual Presented

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mass energy review, applications of interference, holographic optical tweezers, lithography, introduction to mechanics and Newton's laws

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• ### 23 Apr 21 Assorted Topics, Mechanics Intro Actual Presented

1. 1. Today: Interference topics, intro to mechanics Exam #3 is Thursday! 1/3 millimeter Electron Microscope Image of MEMS Force Sensor
2. 2. Quiz 10 (Which has more mass?)
3. 3. Quiz 10 (Which has more mass?) A carbon nucleus is stable / has significant “binding energy”
4. 4. Protons and neutrons weigh LESS when bound together! More decrease in mass + 0 + + + 0 + + 0 0 0 0 Carbon-12 nucleus, Mass = 12 u (by definition) + 0 Single free proton Mass = 1.007825 u Single free neutron Mass = 1.008665 u You need to ADD energy to take apart a C-12 nucleus
5. 7. Protons and neutrons weigh LESS when bound together! More decrease in mass Very significant energy release by fusion of deuterium / tritium
6. 8. Uranium-235 decreases in mass during fission <ul><li>One possible fission reaction is: </li></ul><ul><li>U-235 + neutron  Ba-141 + Kr-92 + 3 neutrons </li></ul>Ending mass = 99.9% of starting mass 0.1% Missing mass = kinetic energy of products (and some gamma rays) <ul><li>Fission of 1000 kilograms of Uranium-235 releases 1 kilogram of mass energy </li></ul><ul><ul><li>Equivalent to a few days of U.S. electrical needs </li></ul></ul>(true: free neutrons do increase in mass)
7. 9. Clicker question—Mass energy available <ul><li>Which reaction can potentially release more energy per nucleon </li></ul><ul><li>More energy can be released per fission event </li></ul><ul><li>More energy can be released per fusion event </li></ul>
8. 10. Immediately, Nuclear Fusion was recognized as an even greater source of energy And of course, hydrogen is a very abundant element!
9. 11. Remember to study quizzes for exam! One topic that we will cover is diffraction and interference of light. Let’s review a little by looking at applications.
10. 12. Laser Diffraction Demo (Repeat) Laser Lens Diffraction Grating Lens Interference pattern on wall Laser Light
11. 13. Clicker Question--Diffraction <ul><li>What kind of diffraction grating are we using right now? </li></ul><ul><li>Single-slit </li></ul><ul><li>Double-slit </li></ul><ul><li>Pinhole </li></ul><ul><li>Multiple slit grating </li></ul>
12. 14. Clicker Question--Diffraction <ul><li>I’m going to show you the pattern from two different apertures. </li></ul><ul><li>Which of the single-slit apertures is narrower ? </li></ul><ul><li>First one </li></ul><ul><li>Second one </li></ul>
13. 15. Laser Diffraction Demo (Repeat) <ul><li>Different diffraction gratings produce different interference patterns </li></ul><ul><li>Changeable gratings allow for changeable (“dynamic”) interference </li></ul><ul><ul><li>Holographic optical tweezers </li></ul></ul><ul><ul><li>Interferometric lithography </li></ul></ul>Laser Lens Diffraction Grating Lens Interference pattern on wall Laser Light
14. 16. Holographic Optical Tweezers for Biology Laser Lens PROGRAMMABLE Diffraction Grating (e.g. LCD) To Microscope, Creating optical tweezers Changing deflection of laser beams
15. 17. You know more physics now about optical tweezers
16. 18. You know more physics now about optical tweezers Focused laser beam Light has momentum! Small plastic bead a little lens! If bead moves left, laser is refracted left equal and opposite force on bead to the right If bead moves right, laser is refracted right equal and opposite force on bead to the left Newton’s third law: every force has an equal force in the opposite direction Arthur La Porta, U. Maryland
17. 19. Can “unzip” DNA double helix with optical tweezers! Requires about 15 piconewtons to unzip DNA This is less than one trillionth the force required to lift your body! (About 1,000 Newtons) 3 “microns” F F 1 2 . . . j
18. 20. Can “unzip” DNA double helix with optical tweezers! Using optical tweezers, we can find where proteins are along a single DNA molecule! Our lab is currently working to unzip DNA molecules extracted from living cells! With protein Without protein Protein F F 1 2 . . . j
19. 21. Brainstorming exercise What are possible uses of optical tweezers?
21. 23. You also have learned physics relevant to the microelectronics industry Photons have energy & can catalyze chemistry Diffraction effects—diffraction limits how small we can go Interference effects
22. 24. Microelectronic circuits are made by photolithography <ul><li>Using specific masks and multiple steps, make millions of tiny transistors and wires </li></ul>http://www.youtube.com/watch?v=BcBNl1cfEis
23. 25. Smaller features = better computer Limited by diffraction of light! Original Mask Tolerable Diffraction Too much diffraction
24. 26. Interferometric Lithography at UNM (CHTM) Porous nanochannels made by CHTM folks These are about 500 nm nano channels (edge-on), whose walls are made of silica nanoparticles, and thus porous. These bright dots are images of lambda DNA in CHTM porous nanochannels. The channels are too big (>500 nm) to stretch them out. Brueck group, CHTM Fluorescent DNA in nanochannels
25. 27. Clicker Quesiton--Diffraction <ul><li>Single-slit diffraction: For a given single-slit width, which will have a wider spread in the output beam? </li></ul><ul><li>Low frequency / long wavelength (e.g. red light) </li></ul><ul><li>High frequency / short wavelength (e.g. UV light) </li></ul><ul><li>Doesn’t matter </li></ul>
26. 28. Clicker Quesiton--Diffraction <ul><li>Single-slit diffraction: For a given single-slit width, which will have a wider spread in the output beam? </li></ul><ul><li>Low frequency / long wavelength (e.g. red light) </li></ul><ul><li>High frequency / short wavelength (e.g. UV light) </li></ul><ul><li>Doesn’t matter </li></ul><ul><li>This is why the industry has moved from visible light to “deep-ultraviolet” (DUV) light for photolithography </li></ul><ul><li>Also: Extremely sensitive (and expensive) machines for placing mask very very close to the wafer </li></ul>
27. 29. The same process for making Pentiums can be used to make tiny machines <ul><li>Microelectromechanical Systems (MEMS) </li></ul>Dust Mite (GROSS!) MEMS Gear Electron micrsocopy image
28. 30. We are using MEMS for biophysics applications -> Measuring tiny forces 1/3 millimeter Electron Microscope Image of MEMS Force Sensor
29. 31. Hooke’s Law for Springs <ul><li>F = k * x </li></ul><ul><li>Force is proportional to stretch of spring </li></ul><ul><li>“ k” is called the “spring constant” in units of Newtons / meter </li></ul>Relationship is violated frequently (think plastic, silly putty, etc.)
30. 32. We used the tiny spring to weigh tiny things 30 micron plastic beads Weight = 100 piconewtons Typical human hair for comparison Force = k * spring displacement k = 1 piconewton per nanometer
31. 33. We used the tiny spring to weigh tiny things Direction of gravity Force = k * spring displacement k = 1 piconewton per nanometer
32. 34. “ Mechanics” <ul><li>Mechanics is the physics of how everyday objects move and respond to forces . </li></ul><ul><li>It was the first well developed field of physics. </li></ul><ul><li>Mathematics are key to mechanics, making the physics extraordinarily powerful (but not simple). </li></ul><ul><li>We are skipping most of mechanics because we don’t have access to the mathematical tools. </li></ul>
33. 35. FORCE …Brainstorming <ul><li>What can forces do? </li></ul>
34. 36. FORCE …What is a force? <ul><li>What can force do? </li></ul><ul><ul><li>Force changes the motion of an object </li></ul></ul><ul><ul><ul><li>gravitational force is responsible for the elliptical orbit of the Earth / Sun. </li></ul></ul></ul><ul><ul><ul><li>frictional force slows down a sliding hockey puck. </li></ul></ul></ul><ul><ul><li>Force causes deformations in an object </li></ul></ul><ul><ul><ul><li>electrical force causes nucleus to deform </li></ul></ul></ul><ul><ul><ul><li>applied force can cause a spring to stretch or compress </li></ul></ul></ul>
35. 37. FORCE …What is a force? <ul><li>What kind of forces are there? </li></ul><ul><ul><li>Fundamental: Gravity, Electromagnetic, strong, weak </li></ul></ul><ul><ul><li>Practical: Gravitational, electrical, magnetic, frictional, drag “stretchy”, contact (hard objects) </li></ul></ul><ul><li>All of these can be measured in units of “force” </li></ul><ul><ul><li>Pounds or Newtons are common. 2.2 lbs. =~ 10 Newtons. (1 kg weighs 10 Newtons on Earth) </li></ul></ul>
36. 38. Clicker Question—units of force <ul><li>Which of these is closest to the equivalent of 1000 newtons of force? </li></ul><ul><li>22,000 pounds </li></ul><ul><li>2,200 pounds </li></ul><ul><li>1,200 pounds </li></ul><ul><li>220 pounds </li></ul><ul><li>22 pounds </li></ul>
37. 39. Clicker Question—units of force <ul><li>Which of these is closest to the equivalent of 1000 newtons of force? </li></ul><ul><li>22,000 pounds </li></ul><ul><li>2,200 pounds </li></ul><ul><li>1,200 pounds </li></ul><ul><li>220 pounds </li></ul><ul><li>22 pounds </li></ul>A 220 pound person weighs 1000 newtons. (The mass would be 100 kilograms)
38. 40. Newton first formalized mathematics of forces <ul><li>Scientists had been thinking about force and motion for centuries before Newton…read about it in the textbook! </li></ul><ul><li>Newton’s three laws of motion </li></ul>http://www.youtube.com/watch?v=9EIZo9egyL4
39. 41. Newton’s first law of motion . <ul><li>Also called the law of inertia . </li></ul><ul><li>An object will continue in a state of rest or uniform motion unless acted upon by an external force </li></ul><ul><li>“ If it doesn’t fit, you must acquit!” </li></ul><ul><li>“ If no force exists, the motion persists!” </li></ul><ul><li>Because of friction and air resistance, there is no obvious demonstration that Newton’s first law is exactly true! </li></ul>This is a key part of why the law was not obvious to those before Galileo and Newton ( A ristotle)
40. 42. Newton’s second law of motion . (fudged a little bit) <ul><li>“ Change in motion is directly proportional to the force acting on the object.” </li></ul><ul><li>“ Acceleration is proportional to force” </li></ul><ul><li>acceleration = force / mass </li></ul><ul><li>a = f / m </li></ul><ul><li>Force = mass x acceleration </li></ul><ul><li>F = m a </li></ul>The TA, Katie, found this to help you remember: http://www.youtube.com/watch?v=dQmYBF_Sd8I&feature=related
41. 43. Lecture ended here (after F=ma video)
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