L&S C70V Final

Basics of the periodic table

92 natural elements and 112 including synthetic ones (live for a very small time); organizes atoms at their most basic level based on proton number

Power= (two formulas)

=E/t =F x v

Plutonium

Artificial: U-238 + neutron --> U-239 - beta decay (electron) -->Np-239 - beta decay --> Pu-239; beta decays: protons flip to neutrons or vice versa; useful for nuclear reactors and bombs; dangerous for its radioactivity and its toxicity

Causes of nuclear reactor disasters

Cause: coolant failed, chain reaction stopped but fission fragments remained that create radioactive sludge in the ground 1. Three Mile Island (PA) in 1979 2. Chernobyl in Ukraine in 1986: coolant stopped --> ignition of graphite moderators --> plume of radioactive smoke drifted over 3. Fukushima in 2011: earthquake --> tidal wave --> shorted out circuits and stopped back up systems

Moderators in reactors

Chemical mixed in with the fuel that tends to slow down the neutrons without absorbing them; popular substances- water, heavy water (deuterium oxide), and graphite; consist of nuclei that are light and don't absorb neutrons but allow them to bounce off --> neutrons lose energy to slow down to speeds expected of their temperature (thermal neutrons), which are more readily absorbed by other U-235 nuclei, which explains why it doesn't have to be as enriched as for bombs

Basics of refrigerator

Cold gas runs through a tube extracting heat from food --> compressor run by electricity takes warmed fluid and compresses it to make its temperature hotter than outside air to expel it --> expansion throttle where gas enters a chamber that is pushed out by a piston to cool it to reenter the cycle; uses mechanical force to reduce pressure in a chamber to reduce the temperature; makes the room it is in hotter because it expels heat when its piston reduces pressure

Helium

Comes from the ground; the second most abundant element in the universe but so little in the atmosphere because it is light and was heated up to escape velocity to leave the earth; expensive and comes from minerals below the ground; initially came from stars

Smoke detectors and radioactivity

Common smoke detectors usually have an alpha particle emitter (travel only 1 cm in the air before they stop); alphas knock electrons off the air molecules (ionize air) --> air is electrically conductive which is measured with a battery since the battery needs the electrons from ionization to complete its circuit; if air is conductive, the alarm does not sound; but, if smoke drifts under the cover, electrons stick to smoke particles --> no longer free to move --> electron current stops --> when it detects this, it sounds the alarm

KE= (formula)

1/2 x m x v^2

G=

10 m/s^2

3 main ways to transport energy

Conduction: energy flows by contact; heat moves from higher temperature to low; endpoint is thermal equilibrium where the temperature is the same; i.e. glass feels colder than plastic bc it conducts heat more quickly out of the hand Radiation: infrared radiation transports heat --> energy moves through empty space via light (possibly invisible) Convection: energy is carried by a moving material, usually gas or liquid; when the hot material reaches some cold things, it usually transfer its energy by contact (conduction); i.e. buoyancy: less dense rises and expands because net upward force balances weight downwards --> why we have clouds, requires gravity and fluid (gas/liquid)

Conductors and insulators

Conductors are materials that conduct electricity well (most metals) --> allows free flow of electrons by propagating slowly upon a path with low resistance --> outer electrons are freely floating which can carry current; insulators are materials that don't conduct electricity well (plastics, rocks, wood, paper, rubber, air) --> electrons held on tightly and electric field is not enough to force electron movement --> high resistance

Cloud chamber basics

Contains super saturated gas that wants to turn into liquid; alpha/beta rays pass through gas --> knock off electrons --> trail of ions --> with lots of water vapor and cool gas, water tends to form droplets on these ions (clouds along the path of radiation); heavy droplets --> bottom of the chamber; cosmic rays come down sometimes

Sun's fusion vs. fusion reactors

Fusion occurs within the sun 4H --> He + 2 positrons + 2 gamma rays + 2 neutrinos --> light particles (positron, gamma, neutrino) escape out of the sun, but other particles collide with other atoms (mostly H) to share their energy with these atoms and heat the Sun --> Sun shines; fusion reactors used magnetic confinement to control the hot hydrogen, let it explode, and cold fusion (not seen as successful), requires large temperatures mainly

Newton's equation for gravity: F=

G(mM/r^2); if double the mass, the force of gravity increase by a factor of 2

"We should conserve energy"

It really means to conserve useful energy like chemical and potential energy; least useful is heat (lack of efficiency)

Newton's 3 Laws

[0: objects in contact tend to reach the same temperature] 1: If an object is at rest, it stays at rest; if an object is in motion, it stays in motion (never happens because of friction) if no external forces act on it; energy is conserved (if you consider all forms, including heat) 2: F=ma; you can't extract heat energy without a temperature difference (efficiency= 1 - temp of cold/temp of hot); heat flow from hot to cold and to get the opposite you have to apply work 3: equal and opposite reaction; nothing can reach a temperature of absolute zero; entropy increases in a closed system

Logarithmic scales

e.g. Richter scale: every increase by 1 is 10 times the movement of the previous value on the seismometer (measures how far the ground moves up and down); 32 times more energetic in an increase in 1; use logarithmic scales (based on power) due to the large range

Avalanche concept

i.e. lightning: form because an electron has a high electric voltage --> breaks off to accelerate through the air --> break another electron off a molecule of air to double the number of moving electrons, which begin to increase exponentially; collisions of electrons with air molecules heat the air and cause it to rapidly expand (thunder) and glow

Binding energy

refers to how strongly the nucleus is bound together; differs between atoms; iron has the highest --> iron catastrophe which is where the star (produces elements) collapses on itself because it cannot produce energy to counter the force of gravity and needs more energy to continue that it cannot get since there is no element with more binding energy than iron

Acceleration

speed is the distance covered by the body in a unit time, and acceleration is the change in velocity per unit time; acceleration is when velocity changes; If the body achieves a constant speed, then the acceleration ceases to exist; even at the top of the trajectory, speed is 0, but acceleration is constant (g near the surface of the earth)

Yellow cake

A type of uranium concentrate powder obtained from leach solutions, in an intermediate step in the processing of uranium ores; it is a step in the processing of uranium after it has been mined, before fuel fabrication or enrichment; after processing of all the non-uranium element; purified as uranium but not enriched; uranium oxide helped make the yellow color of Fiesta ware's plates

Centripetal acceleration and formula

Accelerating even though it has constant speed because it requires a force to constantly change the direction of its velocity; at constant speed, circular motion includes acceleration; a=v^2/r; high g from centripetal acceleration is important for pilots (who can pass out from too much g) and for uranium enrichment using centrifuges (heavier isotopes go to the outside, lighter ones on the inside)

Different types of radiation from radioactive atoms

Alpha: tunneling; He-4 nucleus with a +2 charge; can be stopped by almost anything; when they slow down they usually attract 2 electrons (free or weakly attached) and form helium; least dangerous Beta: weak force; electrons and positrons; require a thin sheet of metal to stop; lighter than alphas, but move so fast that they have energy comparable to them; when they stop after numerous collisions, they usually attach themselves to an atom; dangerous but not as bad as gamma Gamma: packets of high energy photons of light; similar to x-rays but higher E; must be stopped by a thicker force because does not interact with charges and goes right through; travel at the speed of light but carry a million times the energy as a single packet of visible light; high frequency with a small wavelength --> high energy; most dangerous

Angular momentum and formula

Applies to rotational motion; tendency for spinning objects to keep spinning; spinning object keeps changing its angle of rotation; conserved when there are no external torques (amount of twist); L=mvr; ex: spinning will get faster when the radius is decreased, which is showed by an example of a spinning ice skater who brings his hands in

Tokamak

Approach to controlled fusion that addresses the problem of high pressure and resulting explosions that come with heating deuterium and tritium to the necessary temperature to fuse by making hydrogen gas work at a very low density so that the pressure is not very high; magnetic confinement holds hot hydrogen plasma for fusion

Atomic vs. hydrogen bombs

Atomic: uses uranium or plutonium which uses the energy of their nuclei to release energy Hydrogen: uses fusion of hydrogen; aka thermonuclear because the fusion takes place due to high temperature of fission bomb; (1) explosion of fission bomb creates heat (2) heat causes deuterium and tritium to reach energies that overcome their repulsion to each other bc both positive--> fusion (3) fusion releases energy and neutrons --> cause fission in the uranium container of U-238

Basics of heat pump

Basically air conditioner/refrigerator backwards; pumping heat energy from outdoors (making it colder) to bring that energy indoors to make it warmer

2500 REM

Cancer dose; full-body --> certain you will get cancer; used as the baseline to predict the chance that one person will get cancer based on their exposure or the percentage of people that will get extra cancer (20 percent will die from normal cancer) out of a group based on the exposure to each person

Energy

Capacity to do work; anything that can be turned into heat

Escape velocity

Critical speed at which a projectile will be able to escape the Earth's gravity; depends on mass and radius of object you're trying to escape from

Nuclear reactor basics

Device in which a sustained chain reaction takes place that is constant and does not grow; does not involve doubling because only one of the emitted neutrons hits another nucleus to cause fission; power comes out in the form off heat -->boils water into steam --> used to run a turbine; uses mostly U-235 (not as enriched to 238 as needed for a bomb); control rods stop there from being exponential runaway by absorbing neutrons without releasing energy; moderators slow neutrons

Lightning

Discharges lots of electricity quickly; high voltage and high current; can kill or knock down a tree, but too low to really be a source of useful energy

2nd Law applied to efficiency

Efficiency of a heat engine is always less than 100 percent

How windmills work

Efficient at removing energy from wind when they are larger because they can get energy from winds at high elevations; ultimately comes from solar power (temperature differences drive winds); cannot be spaced too closely because they decrease the velocity and increase turbulence

Difference between electric motors and generators

Electric motors have wires wound in a way to create a strong magnetic field which is used to pull or push on a permanent magnet; if the current is periodically reversed, the alternating pushing and pulling can move the magnet in a circle, which is how a motor works; many use two electromagnets --> current is switched so that the force of the stationary magnet on the other pushes the rotating one in circles; can be very efficient as long as thick wires are used Electric generators move a wire through a magnetic field; metal wires have mobile electrons, which move with the wire when it goes through a magnetic field to create current when the wire is moved perpendicular to the length of the wire; nuclear uses chain reaction to produce heat to turn water into steam to drive propellers that drive wires through magnetic field; coal is burned to produce heat to do the same; gasoline burns to do the same; hydroelectric uses water to turn the wheels to push wires; car uses gas engine to turn an axle called a crankshaft to turn the wheel to move the wire

Conservation of energy

Energy that appears to be lost isn't really lost; it is just turned into heat; i.e. number of joules store in the gunpowder is the same after the gun is fired

Second law of thermodynamics

Entropy of a closed system inevitably increases; i.e. easy to convert work with 100% efficiency into heat, but impossible to convert heat into workf

Radioactivity

Explosions of the nucleus in an atom; energy released is nearly 1 million times more than chemical reqctions

Energy= (formula)

F x L, where L is the distance over which force F is added

Fast vs. slow neutrons

Fast: atomic bomb needs fast neutrons (unmoderated) so that it can get through the 80 generations without the bomb blowing itself apart; does not blow apart because not enough time Slow: commercial nuclear reactors depend on slow neutrons because if if the reactor begins to run away (chain reaction begins doubling), the slowness of neutrons limits the explosion since when the temperature rises to a certain point, the atoms are moving faster than the neutrons and the neutrons cannot keep up --> chain reaction stops; cannot give rise to a nuclear explosion; slow neutrons are more likely to be absorbed by u-235 because they feel its nuclear force for a longer time and are more readily pulled by the nuclear force toward the U-235 nucleus

Laser fusion

Figuring out whether large lasers can heat a pellet of deuterium and tritium hot enough to ignite thermonuclear fusion; safe way to have fusion; not yet proven practical; facility cannot be cycled fast enough to create controlled thermonuclear fusion

Fission vs. fusion

Fission refers to splitting of nucleus into two or more large parts and has two forms (spontaneous and induced); spontaneous is when the nucleus behaves like a radioactive nucleus and is almost nonexistent in nature; induced fission can occur if the right nucleus is hit with a neutron and becomes unstable and fissions (basis for nuclear reactors and bombs); fission creates two unequal fission fragments; fusion refers to the coming together of particles; fusion is exothermic, but beyond the iron peak it is endothermic because the star collapses on itself and creates the rest of the elements at a fast rate

Basics of thermometers

Fluid (mercury/alcohol) has a greater coefficient of expansion than its surroundings (glass and air); bulb makes the expansion visible; tube has a vacuum so that air pressure does not stop flow

Thermal expansion

Fractional expansion is constant, while total expansion depends on the size of the thing thats expanding; i.e. bimetallic strip (used for thermostats and turn signals --> in thermostat, heat keeps it bent and heater off and cooling will complete the circuit to turn the heater on)

Natural reactor in Gabon

French discovered a uranium mine in Gabon that had ore that had less U-235 than normal; U-235 had been destroyed by fission 1.7 billion years ago when it was around 3% of the ore, which is large enough for a nuclear reactor; water seeped into the ground to moderate the neutrons --> natural nuclear reactor; overheating --> vaporization of water which stopped moderation --> self-regulating to not blow up; U-235 was burned and dropped below 3% to produce Pu and fission fragments but uranium dropped to a lower level that turned it off

Uranium enrichment methods

Gas diffusion: put U as a gas in a chamber that has high pressure with chamber above with lower pressure and separate by porous membrane that allows 235 Centrifuge: U combined with fluorine to make UF6 gas; spins U with heavier U-238 going on the outside while lighter 235 stays in the middle of the tube and is funneled out Saddam: Calutron- slow method for enriching U-235 from natural uranium in which uranium ions moved in a semicircular path along the C shape bent along this path by strong magnets --> 235 and 238 curve differently and can collect 235; had not achieved necessary enrichment Uranium is preferred over plutonium for terrorists because the design is simpler, but enriching uranium is difficult due to money, development, fragility, and easy to destroy; centrifuge is the method of choice for nuclear proliferation

Dynamos

Generator that gets the electricity for electromagnets necessary for large generators from the generator itself; takes energy to push the wire through the magnetic field --> electric energy that emerges in current and magnetic field comes from energy you put in (not paradox)

Forms of energy

Heat energy, mechanical, electrical, chemical, potential, kinetic, mass; can convert between them

Power= (in EM)

IV

Diet and exercise

Ingest more calories than you burn --> extra goes into fat; ingest less --> lose weight

Intrinsic v. extrinsic qualities

Intrinsic: temperature, pressure (doubling the size of the system does not double the quantity) Extrinsic: heat energy, mass (doubling the size of the system does double the quantity, scales up with amount of quantity)

Dangerous radiation is...

Ionizing radiation (when individual photons have enough energy to ionize a molecule) meaning that it knocks off electrons from atoms; dangerous when it ionizes DNA

Geosynchronous satellite/orbit

Larger radius (from the center of the Earth), larger orbit; orbit is 24 hours with 22,000 mile radius, while moon's orbit is one month with 200,000 mile radius; i.e. TV and weather satellites --> must stay above the same location on the Earth which it can only do by orbiting above the equator

Mass v. weight

Mass is a measurement of how much matter is in an object; weight is a measurement of how hard gravity is pulling on that object; mass is a measure of inertia or sluggishness;same mass on the moon, but 1/5 the weight; astronauts have 0 weight but still the same mass

Semiconductors

Materials that can be made to turn from conductors to insulators and back by applying electricity in a special way; ability to control electric flow makes them useful for electronics from stereos to computers

Superconductors

Materials that have zero resistance at low temperatures which is achieved by immersing them in liquid helium; high-temperature ones are brittle and difficult to manufacture useful wires from them --> could potentially use much more abundant liquid nitrogen to keep them cool; limit to the amount of current they can carry because high current creates high magnetic fields which can destroy superconductivity --> current they can carry depends on cross sectional area

Compass

Materials/instrument that tend to rotate north when suspended; this occurs because the Earth itself is a large magnet and the north pole of the object is being rotated by the magnetism of the Earth; after lodestones, you could create magnets from iron by rubbing a needle on a magnet in one direction or apply a strong magnetic field from an electromagnet to a piece of iron, which could be used as the needle in a compass

Electric current

Measured in amps; is not electrons per second, but is charge passing past a point per second

Electric motor v. generator

Motor turns electrical energy into kinetic (mechanical) energy; generators turn kinetic energy into electric energy

Hunter/monkey demo

Neglecting air resistance and without gravity, an object thrown across a room will continue in a straight line; when gravity is present, the force of gravity's effect can be added in from where it would be with no gravity for each certain time interval to get its actual location; in the same amount of time, the monkey and the bullet will fall to the exact same location due to gravity; does not matter how fast the bullet comes out of the gun...it will just hit the monkey in a higher or lower spot

Ultrasound

Not EM radiation; cannot cause mutations like x-rays and beta rays bc it is high-frequency sound that does not have the capability of delivering enough energy to individual cells to cause them; smallest things you can image with a wave have a size of around the wavelength of the thing you're trying to image

Voltage

Not a measure of energy, but a measure of energy per unit charge (intrinsic quantity meaning that it does not scale with amount); difference between electric potentials; is not dangerous --> current is because it is flow; like pump in water because creates pressure (voltage difference) and current is the rate of flow of water and water wheel that spins turbine does useful work like a battery; makes charges move because they are already moving but nuclei is fixed

Why doesn't Earth and other planets have nuclear fusion?

Not hot enough; 15 million C on the Sun used to fuse nuclei to overcome electric repulsion between the positively charged nuclei but not even the hottest

Composition of atom

Nucleons (protons and neutrons) --> atomic weight (average of all isotopes); Quarks; have either plus or minus 1/3 or 2/3 charge --> protons and neutrons have 3 quarks each --> proton (+2/3 +2/3 -1/3 to give +1 charge) and neutrons (+2/3 -1/3 -1/3)

Black hole

Object whose escape velocity is the speed of light; strong gravity indicates its existence; 2 ways to get one: have lots of mass or pack a moderate amount of mass into a very small radius; can be created when the inner part of a star collapses on its own weight into a small radius

Conservation of momentum

Only applies to an isolated system with no external forces (impulses which is what it takes to move something); Ex: when fire a gun- before firing, the bulllet and gun are at rest with 0 momentum, and, after, the bullet and rifle are moving in opposite directions with exactly opposite momenta (still 0 overall total momentum); ex: sliders- when they collide (1 moving, 1 stationary) motion of moving gets transferred to the other car, when they move as one unit they go half the speed; rocket works by conservation of momentum because they fly by burning fuel downward which allows the rocket to gain the extra upward velocity

Momentum and formula

P=mv; exploding objects have 0 total momentum if they start at rest

Permanent magnets vs. electromagnets

Permanent magnets get their magnetism from electric current within electrons (always spinning --> charge is always spinning --> electric current); ferromagnet's (Fe, Ni, Co) electrons line up and have the same spin direction in which the magnetism adds (as it does not in most materials) to create a permanent magnet; known as permanent because retains magnetism without additional power Electromagnets exert strong electrical force on other currents or on a permanent magnet if wire is arranged in the correct geometry; electric current goes through the electromagnet which causes an attraction between the magnet, creating a current that can be reversed to repel the magnets; usually lightweight to move back and forth quickly; used to lock car doors, speakers, and earphones; latter two: it works by vibrating to the oscillations of current, which makes air vibrate to create sound; superconducting electromagnets can get very strong and widely used in refrigerators and to provide magnetic fields for MRIs

Power vs. energy

Power is the rate of energy transfer (energy/time)

Electric charge

Property of the electron that gives its force; is quantized (exact multiple of the quark charge)

Breeder reactor

Pu-239 in a reactor produces 3 neutrons when only 1 is needed --> extra 2 neutrons are used to created more plutonium with U-238 --> can create more Pu-239 fuel than it consumes; oppositions to breeder reactors: (1) more widespread plutonium which is radioactive and could be diverted to terrorists (2) most efficient ones use fast neutrons, which could create a situation where it explodes like a bomb

Force acting on a body

Push or pull an object exerts on another object; depends also on the time over which the force is exerted; thus, it involves time and magnitude

Heat

Random kinetic motion of atoms and molecules; anything that raises the temperature of a material; usually invisible except Brownian motion (random motion of particles being buffeted around by atoms/molecules) which can be viewed with a microscope

Nuclear waste

Reactor: U or Pu create fission fragments that are often radioactive (waste) --> put in pools to let it cool off --> thick canisters --> wanted to put in Yucca Mountain, but now stored all over the country and won't break or leave for the next couple of decades; after 100 years of storage, there is 10% chance that 10% of it will leak; plutonium only dangerous if turned into small particles or breathed in, not in groundwater Fallout: consists of fission fragments from uranium and plutonium in the bomb; bad if exploded near the ground because mixed in with dirt that goes in the air but settles back down

Circuit breakers

Safety precaution in most homes to prevent currrent from exceeding a safe value; has a wire formed around a bimetallic strip; when the strip heats beyond the allowed limit, it bends away and breaks the connection to another wire; differs from fuse because it can be reset (strip goes back in place with the wire) after it has been cooled

Electrolysis

Separation of water into hydrogen and oxygen

First Law of Thermodynamics

Similar to conservation of energy; takes into account different kinds of energy; heat put into the system (Q)=energy gain of the system (E) + work done by system on surroundings (W)

Magnets

Simplest ones have two ends (north and south pole); like charges repel and opposite charges attract; force of magnets (magnetism) is based in moving charges --> force between steady electric currents rather than stationary charges; magnetic force law: two short lengths of current carrying wire has a force that is inverse square (double the distance, the force will weaken by a factor of four); changing magnetic field creates electric current

Energy vs. temperature

Temperature is heat energy per atom; intrinsic quality (like density)

Phases of matter

Solid --> liquid --> gas --> plasma (free electrons and atoms, i.e. candle flame); most solids are more dense than liquids [not ice] --> when water crystallizes into ice lattice, there is lots of open space, whereas liquid molecules can simply slip past each other allowing ice to float; at the temperature of phase change, energy goes into changing phase meaning the temperature is the same

Connection between magnetism and electricity

Steady current--> magnetic field; changing magnetic field --> current (induction); current carrying wire in a magnetic field has a mechanical force acting on it, which is the basis for generators and motors

Potential energy

Stored energy; i.e. gravitational potential energy near the Earth's surface (E=mgh)

T (in Kelvin) =

T (in C) + 273; used in the ideal gas law

Linear hypothesis

The assumption that the line represents the true chance of cancer even at very low doses; 2 ideas: there is no lowest threshold on danger of cancer from radiation dose and damage is cumulative (cells cannot repair themselves); due to uncertainty and statistical fluctuations--> it can't be proved true; one additional cancer is significant, even if it is not statistically significant (why many believe we should assume linear hypothesis)

Regenerative braking

Turns mechanical motion into electrical (stored chemical energy in the case of hybrids); brakes turn the energy of motion into heat

Half life

The rule that radioactive atoms decay half of their current total over a period that depends on the isotope; after each successive half-life, half of the current totals of that material decay; reduction of radiation following this rule=radioactive decay; probabilistic in essence, not causal, since it is a measure of tendencies

Weightlessness in space

They have most of the weight (95%) of their weight on Earth, but feel weightless; astronaut in orbit is in a perpetual state of falling because at high velocities, space capsules curve towards the earth, but since the earth also curves, astronaut misses the edge of earth --> gravity makes path of capsule curve downwards, but since it matches the curvature of the earth, it misses the earth and stays at a constant height; this causes the weightless feeling because the astronaut is constantly falling with the capsule (like in the elevator) and feel no force on their feet or on their shoulders from their head

Air friction

To keep car from being slowed by air resistance, the engine must exert an equal and opposite force, which wastes gasoline --> streamlining the shape of cars to reduce air resistance since air molecules will bounce obliquely; driving slower can also reduce air resistance and save gas since you are driving not as fast and creating less resistance; force proportional to the surface area and to the speed at which the object is moving through the air; contains a terminal speed; energy is still conserved, but some energy is converted to heat

Solenoid

Type of electromagnet where current flows around wire and creates a magnetic field, which aligns electrons in the iron core to increase magnetic field; can be switched and is used in car doors

Chain reaction

U-235, when bombarded by a neutron, breaks into 2 fission fragments which each release 2 neutrons because there are many neutrons in heavier isotopes that make it unstable; these neutrons make chain reaction possible --> if other U-235 nuclei nearby, neutrons might hit them and cause additional fissions --> doubling process; exponential growth; if chain reaction proceeds, it will split into 84 generations; plutonium takes fewer generations because each fission releases 3 instead of 2 neutrons

Joule

Unit of energy; kg m^2/s^2

Fermi's uranium piles

Uranium pile was the first nuclear reactor built by Enrico Fermi underneath Stagg Field at UChicago; Graphite in them used as a moderator --> slow down the neutrons because it could easily penetrate graphite and knock neutrons around in carbon to slow them to thermal speeds (molecules in air) which gives them a greater probability of breaking uranium nucleus apart

Uranium vs. plutonium bomb

Uranium: "gun" type --> piece of U 235 shot by a cannon at another piece of 235--> combination above the critical mass, which started a fission chain reaction that released nuclear energy causing the explosion; not tested because so simple; cylindrical shape; requires highly enriched uranium (U-235) Plutonium: Pu-240 is highly radioactive and can predetonate (explosion before completion of chain reaction) --> implosion; challenge was getting the plutonium to compress so that the chain reaction would go to completion; Pu arranged in a hollow shell with explosives on the outside that drive the shell into a blob and compress it which pushes the atoms close together that neutrons produced in the chain reaction are unlikely to be able to leak between them --> smaller critical mass; spherical shape

Geiger counters

Use an avalanche of electrons in a Geiger tube; each click is a cosmic ray; muons (larger particle with same charge as electron that is created artificially through nuclear reactions) ionizes gas to create electrons that are connected to a battery drift to opposite side of charge (positive) and continue to create an avalanche of electrons ionizing one another and creating electrons which creates the sound heard in it

Principle of hydrogen fuel cell

Used for its high amount of chemical energy per gram relative to gasoline and the fact that its only waste product is water; fuel cell converts chemical energy directly into electricity; advantage is that you provide more fuel (hydrogen or oxygen)

Carbon dating

Used to measure the age of fossils; c-14 (the radioactive isotope measured) absorbed into plants from the atmospheric cosmic rays that we eat; when we die, the c-14 decays and is not replaced; i.e. if discovered and has 6 decays per minute instead of 12, the fossils are as old as a half-life of c-14; only useful for ages of about 10 half lives because it is difficult to measure lower rates

Ohm's law

V=IR

Free fall

When only gravity acts on an object; everything accelerates at g regardless of mass

Relationship between power and changing gears in a car using a clutch

a mechanical device that engages and disengages the power transmission, especially from driving shaft to driven shaft