External Knowledge Training
- Most of the content of this page was first published on the FB page with the same name.
- This page is moderated by John Eagles.
Physics - Introductory Berkeley course
- All notes by John Eagles
1 Introduction
Today i started watching this introductory course in physics. It's a UC Berkeley course given by Richard Muller. He explains physics without using many equations. In this particular lecture he comments quite a bit on 9/11 related physics and dwells on terrorist shoe bombs. He advises the government in such matters, so his views seem a bit politically colored. But he really knows how to present laws of physics in a very understandable and close-to-life manner. I've learned quite some new things from watching this lecture.
2 Solar technology, coal reserves
Summary of topics lectured about:
- Calories of food
- Peripheral vision of the eyes detect especially motion
- Solar technology
- Tilt of the earth & the seasons
- Global warming in relation to the forming of clouds. When the climate heats up, more clouds may form and may counter the greenhouse effect.
- Canada is 2nd in the world after Saudi Arabia for its oil reserves, but Canada has it stored in oil sand and it's more expensive
- Natural gas & shale gas in comparison to oil
- Coal reserves: The USA has most reserves, then comes Russia and then China, Australia and India. These reserves are big in terms of energy compared to the world's oil reserves.
- Coal and methane can turned into gasoline, but it's still risky in case the oil prices are lowered.
- In politics, there's conflict between the issues of global warming and energy security.
- Coal is the cheapest form of energy.
- IPCC errors
- Sequestering CO2 and making clean use of coal
- CCS = Carbon Capture & Storage
3 Temperature scales
Topics in this video:
- Size of atoms
- Density of atoms
- What makes atoms move, what gives them the kinetic energy?
- Temperature = how much energy do things have
- Thermometers
- Scales of Celcius, Fahrenheit
- Liquid nitrogen experiments
- There are ca 1000 x more molecules in a fluid than in a gas of the same substance per volume
- Temperature of absolute zero on the Kelvin scale means there is no energy
- In the Kelvin scale the amount of energy is proportional to the temperature
- A fire extinguisher has liquid CO2
- Your subjective temperature measurement
- Hot air rises because it's less dense
- Conduction, convection, radiation
Lecturer is Bob Jacobsen
4 Thermodynamics intro
- The ideal gas law (relationship between volume & temperature)
- Movements of small and bigger molecules and atoms
- Energy efficiency of engines
- Refrigerators
- Air conditioners
- Entropy = a measure of disorder
5 Satellites, gravity
This lecture is about:
- Friction
- Movements of satellites
- Why frisbees and airplane wings lift
- Satellites move with 5 miles per second. They are falling but because the earth is curved, they fall with the earth curve
- Rockets escape velocity
- Gravity force between two people near to each other is ca mass of a mosquito
- What does it mean to be weightless
- How do spy satellites work. They have to be close to the ground. It takes them 1 1/2 hour to orbit the earth one time.
- Unmanned drones
- Weather and tv satellites orbit the equator at 22000 miles high and need 24 hours for one cycle: Geostationary satellites
- 24 GPS satellites go around in 12 hours.
6 Newton's laws, inertia, circular motion
Topics explained in this lecture, illustrated with several experiments:
- Newton's laws
- Inertia
- Circular motion
7 Radiation, radioactivity
- Ionizing radiation knocks electrons off atoms.
- We're exposed to some amount of ionizing radiation all the time.
- Tritium is used in some watches.
- Damaging of DNA is what causes cancer.
- Sieverts - Grays - rems.
- 2500 rems (25 Sieverts) on average causes 1 fatal cancer. It's a probability.
- Radiation illness - requires much less than a dose causing cancer.
- About percentages of increase of cancer because of radioactivity.
- Alpha rays don't penetrate deeply, are stopped by the skin.
- X-rays.
8 Global warming, radioactive rays, radiocarbon dating
- Categories of believers and non-believers in global warming.
- Errors in IPCC reports
- He quotes research stating that organic food is unhealthy?!?
- Chemotherapy & radiation therapy against cancer, how does it work?
- The energy release of exploding a nucleus is typically 1 million times more than energy released in chemical reactions.
- In the early universe almost all atoms probably were explosive or radioactive.
- Radiocarbon dating with C14, having a half-life time of 6,000 years. C14 is in the atmosphere because of cosmic radiation affecting C atoms. Living organisms take in a percentage of these C14 atoms. The amount of C14 in the atmosphere is constant.
- Potassium-Argon dating: A dating method using rocks.
- Beta rays are fast electrons.
- Alpha rays consist of small nuclei of 2 protons and 2 neutrons that form He atoms when the rays are stopped.
- Gamma rays are penetrating, not ionizing colliding particles. They pass through things. They knock off electrons and are very energetic.
- X rays are the same as gamma rays but more energetic. X-ray photos create shadows.
9 Nuclear reactors, uranium, chain reactions
This lecture is about:
- How to get useful energy from radioactive elements.
- Chain reactions and nuclear fission.
- U235 is more radioactive than U238, but there's much less of U235 on earth (U = uranium).
- Enrichment of uranium is removing what you don't want, for example by using centrifuges.
- Depleted uranium.
- Natural and oldest man-made nuclear reactors.
- The nature of chain reactions.
10 Nuclear waste, fusion reactors
- Where to store nuclear waste?
- Safety measures for nuclear plants.
- Spent fuel rods and spent fuel storage installations.
- Nuclear waste transport.
- Waste from uranium mines.
- Fusion reactors are still not commercially operated.
11 Graphene, electricity basics
- Four different carbon bonds.
- Graphite and graphene. Graphene is a newly produced one-layer sheet of graphite.
- Sparks from static electricity.
- Voltage, currents, resistance.
- Fuses and circuit breakers.
- Electrocution.
- Fibrillation of the heart.
- AC and DC currents.
12 Magnetism
- What is magnetism?
- Rare-earth magnets have transformed society.
- Rare-earth minerals.
- The earth is a magnet.
- Magnetism comes about when there is a moving charge.
- Magnetic recording, hard disks, credit cards.
- Electric generators = moving wires pass a magnet.
- Transformers.
- Voltage is energy per electron.
- Magnetic levitation.
13 Scientific implications of magnetism - Electrical power
- Power = voltage x current.
- A moving magnetic field makes voltage and provided there is a conductor, a current.
- Alternating currents and direct currents (AC and DC).
- Edison's first promoting of his electric bulbs.
- High-voltage wires.
- Smart grids.
14 Waves
- Seismographs measure the shaking of the ground.
- Atoms are basically a kind of waves, quantum waves.
- A particle is a wave.
- When you shake the vacuum it becomes a wave.
- A wave is moving energy.
- The old concept of 'aether' is now renamed 'vacuum.'
- Different types of waves.
- Earthquakes & tsunamis.
There's a funny interruption of the lecture because of student demonstrations.
15 More about waves
- Waves have three characteristics:
- Amplitude (height or size)
- Energy (intensity or power)
- Speed (small and big waves travel at the same speed)
- Strings of music instruments.
- Piano tuning.
- Interference of sound waves.
- Sound waves.
- Interference of FM radio waves.
- Mirages.
16 Mechanical waves
- Mechanical waves transport energy through a medium by elastic deformations.
- Characteristics of mechanical waves:
- The medium itself has no position, oscillates around a fixed position.
- Energy is required to create a wave. The wave transports the energy.
- Waves can transmit information.
- Waves travel with a fixed speed for a given medium (wave speed).
- A wave pulse is a single propagating disturbance.
- Periodic waves repeat regularly.
- Frequency = cycles per second (Hertz).
- Mechanical waves require a medium (inertia of the medium), and a form of restoring force (pushing the medium back to a starting position).
- Superposition of waves: Bouncing waves don't affect each other in terms of the speed with which they travel and the energy they carry.
- Standing waves form when two identical waves travel in opposite directions.
- Standing waves on guitar strings.
- 1st, 2nd, 3rd harmonics on strings.
17 Sound, open and closed pipes
- Sound is longitudinal or compression waves. They can be through any medium with molecules (gas, liquids, solids), not a vacuum.
- Sound is pressure waves, or alternating regions of high and low pressure.
- Speed of sound in air is ca. 340 m/s.
- Air inside a pipe, shock waves inside a pipe.
- The closed end in a pipe always feels the maximum pressure of the wave.
- At the open end of a pipe the molecules are free to move. It's a pressure node, the pressure doesn't change.
- Wind instruments are resonant pipes, open or closed.
- A flute is an open pipe.
- A clarinet is a closed pipe.
- Open pipes have all harmonics.
- Closed pipes have only odd harmonics.
- Beats.
- Doppler effect.
18 Electricity
- Electricity is transfer of power or information by electrical forces.
- Electrostatic force: A fundamental force of nature (like gravity).
- Applications:
- transfer of power
- storing energy in batteries
- run appliances
- light, heat
- transportation
- computers, telecommunication, entertainment
- This force comes from electrical charges.
- Electrons have about 1/2000th of the mass of neutrons and protons.
- Electric charges come in two types: Positive and negative.
- Protons and electrons have exactly equal and opposite charges.
- There is a fundamental unit of charge.
- Electrons move much easier than protons.
- Conservation of charge:
- The universe has no net charge (is what is believed)
- We cannot create a positive or negative net charge
- The electrostatic force is both attractive and repulsive.
- The gravitational force is only attractive.
- Electrostatic force : gravity = 4 x 10 to the 42 : 1, so the electric force is much stronger.
- Conductors and insulators
- Electrostatic potential energy.
19 Electrical current & circuits
- Voltage = Potential energy / charge.
- Batteries = Chemical charge pump. Chemicals store energy which is converted to voltage.
- Electrical outlets: The ground of an outlet is literally connected to Earth. It is to keep you and the socket at the same voltage.
- Solar cells: Directly convert sunlight into electrostatic charge.
- For a voltage to provide power, a charge must flow. This is an electrical current.
- Negative charges (electrons) flow from negative to positive. The currents flows in the other direction.
- Electrical circuits:
- Current is usually confined to flow in wires to appliances.
- No current can flow in an open circuit.
- Electrical power:
- Voltage = Potential energy / charge
- Current = Charge transfer / time
- Power = Voltage x current
- Resistance limits the amount of current flow through a circuit for a given voltage.
- Voltage drop
- Ohm's law: Voltage drop = current x resistance.
- Current = Voltage drop / resistance.
- Power lost = current2 x resistance
20 Magnetism
- Is closely tied to electricity.
- Simple magnets have some analogies to electrical charges.
- A magnetic 'charge' is called a magnetic pole.
- Two types of poles: North and South.
- These poles always appear in opposite pairs. We call this a dipole.
- Magnetic dipoles are similar to electric dipoles.
- But there is one major difference: Electric positive and negative charges can exist independently but magnetic monopoles don't exist.
- Electromagnets:
- Oersted in 1820 discovered that electric currents produce magnetic fields.
- On the microscopic level electrons orbit in an atom causing electrical currents.
- For most atoms these currents cancel because electrons orbit in different directions.
- Iron is an exception. Multiple electrons in iron atoms are orbiting in the same direction.
- Each atom is a little atomic magnet.
- Magnetism is a product of electrical forces.
- Magnetic materials, iron and steel, consist of many microscopic atomic magnets. These usually are not aligned.
- Faraday showed that a changing magnetic field produces electrical currents.
- And electrical currents produce magnetic fields.
21 Light
- How do we see an object? Light from the object must enter our eyes as a source of light, as reflected light or as an optical image using lenses or mirrors.
- Light is both a wave and a particle, but light doesn't need a medium to travel.
- Light interacting with a surface, for ex. water: Light can get absorbed, bounce off or be reflected, pass through or be refracted.
- Two types of reflection:
- Specular reflection is off a smooth surface, like mirrors. Light is scattered in one direction.
- Diffuse reflection is off a rough surface (most surface). Light is scattered in all directions.
- Selective absorption: Some colors are preferentially absorbed, other colors are reflected.
- Without atmosphere we would see the sky as black. Air preferentially scatters blue light over red light.
- Refraction: Light travels slower in any material. The light will turn when it enters the new medium.
- Violet light turns more than red light.
- Rainbows.
- Total internal reflection - light can stay trapped in a denser medium. Application of this principle in fiber optics.
- Lasers are coherent light. All laser light has one color and the light travels all in one direction. It is very intense.