Today: Interference topics, intro to mechanics

Exam #3 is Thursday!

1/3 millimeter

Electron Microscope Image of MEMS Force Sensor

Quiz 10

(Which has more mass?)

Quiz 10

(Which has more mass?)

A carbon nucleus is stable / has significant “binding energy”

Protons and neutrons weigh LESS when bound together!

Mo

re d

ecre

ase

in m

ass

+

0

+++ 0

+

+

00 00 Carbon-12 nucleus,

Mass = 12 u (by definition)

+

0

Single free protonMass = 1.007825 u

Single free neutronMass = 1.008665 u

You need to ADD energy to takeapart a C-12 nucleus

Protons and neutrons weigh LESS when bound together!

Mo

re d

ecre

ase

in m

ass

Very significant energy releaseby fusion of deuterium / tritium

Uranium-235 decreases in mass during fission

One possible fission reaction is:

U-235 + neutron Ba-141 + Kr-92 + 3 neutrons

Ending mass = 99.9% of starting mass0.1% Missing mass = kinetic energy of products

(and some gamma rays)

Fission of 1000 kilograms of Uranium-235 releases 1 kilogram of mass energyEquivalent to a few days of U.S. electrical needs

(true: free neutrons do increase in mass)

Clicker question—Mass energy available

Which reaction can potentially release more energy per nucleon

A) More energy can be released per fission event

B) More energy can be released per fusion event

Immediately, Nuclear Fusion was recognized as an even greater source of energy

High mass atoms can yieldenergy via nuclear fission

Low mass atoms can yieldenergy via nuclear fusion

Energy availablefrom U-235

Energy availablefrom

hydrogen fusion

And of course, hydrogen is a very abundant element!

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.

Laser Diffraction Demo (Repeat)

LaserLens

Diffraction Grating

Lens Interference patternon wall

Laser Light

Clicker Question--Diffraction

What kind of diffraction grating are we using right now?

A) Single-slitB) Double-slitC) PinholeD) Multiple slit grating

Clicker Question--Diffraction

I’m going to show you the pattern from two different apertures.

Which of the single-slit apertures is narrower?

A) First oneB) Second one

Laser Diffraction Demo (Repeat)

Different diffraction gratings produce different interference patterns

Changeable gratings allow for changeable (“dynamic”) interference

Holographic optical tweezers

Interferometric lithography

LaserLens

Diffraction Grating

Lens Interference patternon wall

Laser Light

Holographic Optical Tweezers for Biology

LaserLens PROGRAMMABLE

Diffraction Grating(e.g. LCD)

To Microscope,Creating optical tweezers

Changing deflection oflaser beams

You know more physics now about optical tweezers

You know more physics now about optical tweezers

Focused laser beam

Light hasmomentum!

Small plastic beada little lens!

If bead moves left, laser is refracted leftequal and opposite force on bead to the right

If bead moves right, laser is refracted rightequal 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

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)

F

F

1 2...j

3 “microns”

Can “unzip” DNA double helix with optical tweezers!

Using optical tweezers,we can find where proteins arealong a single DNA molecule!

Our lab is currently working to unzip DNA molecules extracted from living cells!

F

F

1 2...j

With protein

Without protein

Protein

Brainstorming exerciseWhat are possible uses of optical tweezers?

“Knitting DNA” http://www.youtube.com/watch?v=v97MesU3Zkw&feature=related

Video game http://www.youtube.com/watch?v=jCdnBmQZ6_s&feature=related

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

Microelectronic circuits are made by photolithography

Using specific masks and multiple steps, make millions of tiny transistors and wires

http://www.youtube.com/watch?v=BcBNl1cfEis

Smaller features = better computerLimited by diffraction of light!

Original Mask Tolerable Diffraction Too much diffraction

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

Clicker Quesiton--Diffraction

Single-slit diffraction: For a given single-slit width, which will have a wider spread in the output beam?

A) Low frequency / long wavelength (e.g. red light)

B) High frequency / short wavelength (e.g. UV light)

C) Doesn’t matter

Clicker Quesiton--Diffraction

Single-slit diffraction: For a given single-slit width, which will have a wider spread in the output beam?

A) Low frequency / long wavelength (e.g. red light)B) High frequency / short wavelength (e.g. UV light)C) Doesn’t matter

This is why the industry has moved from visible light to “deep-ultraviolet” (DUV) light for photolithography

Also: Extremely sensitive (and expensive) machines for placing mask very very close to the wafer

The same process for making Pentiums can be used to make tiny machines

Microelectromechanical Systems (MEMS)

Dust Mite(GROSS!)

MEMS Gear

Electron micrsocopy image

We are using MEMS for biophysics applications-> Measuring tiny forces

1/3 millimeter

Electron Microscope Image of MEMS Force Sensor

Hooke’s Law for Springs

F = k * x

Force is proportional to stretch of spring

“k” is called the “spring constant” in units of Newtons / meter

Relationship is violated frequently (think plastic, silly putty, etc.)

We used the tiny spring to weigh tiny things

30 micron plastic beadsWeight = 100 piconewtons

Typical human hair for comparison

Force = k * spring displacement

k = 1 piconewton per nanometer

We used the tiny spring to weigh tiny things

Direction ofGravity 300 pN

Wieght standard beads areout of field of view on otherset of gratings

Direction of gravity

Force = k * spring displacement

k = 1 piconewton per nanometer

“Mechanics”

Mechanics is the physics of how everyday objects move and respond to forces.

It was the first well developed field of physics.

Mathematics are key to mechanics, making the physics extraordinarily powerful (but not simple).

We are skipping most of mechanics because we don’t have access to the mathematical tools.

FORCE…Brainstorming

What can forces do?

FORCE…What is a force?

What can force do?

Force changes the motion of an objectgravitational force is responsible for the

elliptical orbit of the Earth / Sun.

frictional force slows down a sliding hockey puck.

Force causes deformations in an objectelectrical force causes nucleus to deform

applied force can cause a spring to stretch or compress

FORCE…What is a force?

What kind of forces are there?

Fundamental: Gravity, Electromagnetic, strong, weak

Practical: Gravitational, electrical, magnetic, frictional, drag “stretchy”, contact (hard objects)

All of these can be measured in units of “force”

Pounds or Newtons are common. 2.2 lbs. =~ 10 Newtons.(1 kg weighs 10 Newtons on Earth)

Clicker Question—units of force

Which of these is closest to the equivalent of 1000 newtons of force?

A) 22,000 poundsB) 2,200 poundsC) 1,200 poundsD) 220 poundsE) 22 pounds

Clicker Question—units of force

Which of these is closest to the equivalent of 1000 newtons of force?

A) 22,000 poundsB) 2,200 poundsC) 1,200 poundsD) 220 poundsE) 22 pounds

A 220 pound person weighs 1000 newtons.(The mass would be 100 kilograms)

Newton first formalized mathematics of forces

Scientists had been thinking about force and motion for centuries before Newton…read about it in the textbook!

Newton’s three laws of motion

http://www.youtube.com/watch?v=9EIZo9egyL4

Newton’s first law of motion.

Also called the law of inertia.

An object will continue in a state of rest or uniform motion unless acted upon by an external force

“If it doesn’t fit, you must acquit!”

“If no force exists, the motion persists!”

Because of friction and air resistance, there is no obvious demonstration that Newton’s first law is exactly true!

This is a key part of why the law was not obvious to those before Galileo and Newton (Aristotle)

Newton’s second law of motion. (fudged a little bit)

“Change in motion is directly proportional to the force acting on the object.”

“Acceleration is proportional to force”

acceleration = force / massa = f / m

Force = mass x acceleration

F = m aThe TA, Katie, found this to help you remember:http://www.youtube.com/watch?v=dQmYBF_Sd8I&feature=related

Lecture ended here (after F=ma video)