Phys-273-Notes - Lecture notes 1-12 PDF

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Lesson 1: Introduction to Energy Work and Energy: Work: transfer of energy Force (F) x Distance (D) The word work means many things in everyday life The transfer of energy Ex. If a guy pushes a box across the floor transferring energy into a box Energy: ability to do work Types of Energy: 1) Potenti...

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Lesson 1: Introduction to Energy Work and Energy: Work: transfer of energy = Force (F) x Distance (D)  The word work means many things in everyday life  The transfer of energy  Ex. If a guy pushes a box across the floor  transferring energy into a box Energy: ability to do work Types of Energy: 1) Potential Energy: energy an object has that’s associated with its position when there’s some force acting on it (a type of mechanical energy) Ex. Gravitational potential energy: the higher up an object is, the more gravitational potential energy it has 2)   

Kinetic Energy: energy an object has due to its motion (K = 1/2mv2) Depends on mass and velocity of the object Depends on mass and velocity squared Type of mechanical energy

3) Chemical Energy: energy stored in certain chemicals or materials that can be released by chemical reactions Ex. Burning of wood, paper, coal, natural gas or oil releases chemically stored energy in the form of heat energy Other examples: charged electric batteries, food in stomach 4) Thermal/Heat Energy: energy associated with random molecular motions within any substance  Increase of thermal energy = increase in temperature and conversely a decrease in thermal energy = decrease in temperature 5) Electric Energy: energy that is stored by changes (positive/negative) in their electric fields (a type of potential energy) Ex. On a stormy day, there’s a charge separation between the ground and the clouds  difference where there’s more negative on the clouds and more positive on the group set up an electric energy which can then be transformed into other types of energy 6) Electromagnetic Radiation: light in the form of a wave that carries energy  It can be visible or not (one small range/band of spectrum = visible)

7) Nuclear/Mass Energy: stored energy in some amount of mass (E=mc2)  Discovered by Einstein when he was developing his theory of special relativity when predicted that there is a relationship between mass and energy (mass can be converted into energy and energy can be converted into mass)  Important principal in looking at energy associated with nuclear reactions  c = 30,000km/second = 2.998 x 108 m/s Units of Energy: 1) Joule (J): metric unity of energy where one metric unit of force (Newton) is acting through one metric unit of distance (metre) = J = N.m 2) British Thermal Unit (BTU): amount of heat energy required to raise temperature of 1 pound of water by 1 degree of Fahrenheit  Often encountered in a discussion of fuel and insulation  Based on the amount of heat which must be given to a known amount of water to increase its temperature by a given amount 3) Calorie (C): amount of energy required to raise the temperature of 1 gram of water by 1 degree Celsius or the amount of energy given off when 1 gram of water cools by 1 degree Celsius *NOTE: In North America, when you see the amount of energy stored in food as “calories”  kilocalories 4) Foot-pound: no longer a common unit of energy 5) Electron-Volt (eV): amount of energy an electron gains if accelerated by a 1-V electric potential  Very small amount of energy which is useful when working with tiny charged particles like electrons

Lesson 2: Energy Transfer & Conservation of Energy Transfer of Energy: (aka energy transformation) the process of changing one form of energy to another Ex. Santa on a sled on top of a mountain sliding down to the bottom  Top of the hill = high gravitational potential energy due to high altitude and no kinetic energy  Bottom of the hill = some kinetic energy gained due to some movement  Where did the kinetic energy come from? From the gravitational potential energy that is transformed into kinetic energy (amount of KE gained = amount of PE lost)

Energy flow: used to keep track of the transfer of energy where one form of energy is transformed into another type of energy (there can be many energy transfers) Ex. A simple energy flow: a girl starting from rest and pushes a box across the floor until she is moving quickly (0KE to some KE)  Applied force (work on box)  kinetic energy Ex. A complex energy flow: 1) Energy is produced from the sun (due to nuclear fusion) = nuclear energy 2) Energy is transported into the Earth in the form of electromagnetic energy (light) 3) Electromagnetic energy is converted into chemical energy via photosynthesis 4) Chemical energy is converted into a different form of chemical energy that can be absorbed by humans in the form of plants 5) The chemical energy absorbed by humans can be used to apply force onto a box 6) Work is done on the box which increases kinetic energy

Conservation of Energy Law of Conservation of Energy: the total energy of an isolated system CANNOT change  Isolated system = a system where energy cannot enter or leave (there should always be the same amount of energy)  Same amount of energy does not mean that there is always the same TYPE of energy (total energy can transfer from one type to another)  Total energy is conserved meaning it can be transferred from one form to another, but it CANNOT be destroyed nor created Ex. A lightbulb is attached to a battery in a perfectly insulated opaque box (no heat or light can get out) Energy flow: chemical energy (inside the battery)  electrical energy (voltage across battery)  thermal energy (current heats light)  electromagnetic energy (both visible and nonvisible light) 

Where does the energy go? A decrease in chemical energy results in an exact increase in both thermal and electromagnetic energy = conservation of energy

Ex. Same example as above but the lid of the box is taken off Energy flow: chemical  electrical  thermal  electromagnetic 

Where does the energy go? A decrease in chemical energy results in an increase in both thermal and electromagnetic energy BUT no conservation of energy because some light/heat has left the box since it wasn’t an isolated system (loss of energy)

Power: the rate at which energy is consumed or produced (amount of energy/time)

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P = Energy (J)/time (s) Measures how fast work gets done Metric unit = Watts (W) = 1J/s

Ex. Appliances that heat up tend to be highest power. A hairdryer is approximately 1500W. How much energy is used by a hairdryer in 5 mins? 1500W = 1500J/s

5 mins = 5x60 = 300s

P = E/t 1500J/s = E/300s E = 450,000J = 450kJ How does that compare to a 20W TV? A hairdryer uses 75x more energy E= 20J/s x 300s = 6000J = 6kJ Ex. Imagine a motorcycle accelerates from a stop sign to a speed of 50km/h. There is power being produced and power being consumed. Explain in terms of energy increase and decrease Power produced in engine = a decrease in chemical energy (fuel of motorcycle) Power consumed = increase in kinetic energy (motorcycle and rider)

Lesson 3: Thermodynamics, Heat, Engines & Power Generations Laws of Thermodynamics: First Law of Thermodynamics: states that energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another Second Law of Thermodynamics: states that the changes in entropy in the universe can never be negative (irreversible) and that heat always flows from hot objects to cold objects Ex. A hot piece and a cold piece of metals are stuck together which causes heat transfer from the hot piece into the cold piece until eventually they are the same temperature Ex. A compressed bottle of air shoot some air out of the bottle distributing air in a uniform manner (won’t see air compressing itself into a bottle therefore not irreversible)

Entropy: everything in the universe eventually moves from an ordered state to random state and entropy is the measurement of that change  Less order = more randomness = higher entropy  The total entropy of a system CANNOT be negative (cannot decrease) Ex. Diffusion by dropping sugar cubes inside a glass of water  over time, the sugar cubes dissolve and sugar distributes into the system

Ex. Energy is stored in a battery inside a cool box where the system is well ordered but as the energy inside the battery starts to decrease, there’s more thermal energy (random motion of molecules) inside the box  the total energy of the system remains the same BUT there is less useful energy inside the box and this is an irreversible change since we cannot put energy back into the battery

Heat Engines: the idea of taking thermal energy (heat) and converting it into mechanical energy Mechanical Equivalent of Heat: burning a match  release of thermal energy  The heat energy released from burning a single match is about the same amount of energy required to lift a pint of beer up to the tallest building top in Montreal  This heat energy must be captured and converted into mechanical energy Something we do often: Fossil fuels  used for direct heat and light OR used for heat engines  Heat engines can use fossil fuels and convert them into mechanical energy to either produce electrical energy OR use it for transportation or for the industry Energy Content of Fuel: burning hydrocarbons releases heat energy through 2 chemical reactions, which leaves us with water, carbon dioxide and thermal energy: C + O2  CO2 + thermal energy H2 + O  H2O + thermal energy Ex. Burning heptane: C7H16 + 11O2  7CO2 + 8H2O + 1.2 million calories/100g of C7H16 (heat of combustion) Heat Engine: any device that can take energy from a warm source and convert a fraction of this heat source into mechanical energy  It relies on a temperature difference between the heat source (hot) and a heat sink (cold)

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The efficiency of a heat engine tells us how much of the input heat energy is turned into useful mechanical energy (since not all of input energy can be turned into mech energy due to 2nd law of thermodynamics)

Ex. For every 1000J of energy put into the heat source, 50J is converted into mech energy Efficiency = (work done/energy put into system) x 100% = (50/1000) x 100% = 5% 

Nicolas Leonard Sadi Carnot (French physicist) proved that the best efficiency possible by heat engine is: [1 – (Tcold/Thot)] x 100%

*NOTE: temperature used must be in Kalvin (1K = -273C) Ex. Typical temperatures in a coal firmed electric power plant might be 825K in the boiler (source) and use cold water-cooling tower (sink) at 300K. What is the efficiency that could ever be possible in this type of power plant? Ebest = [1- (Tcold/Thot)] x 100% = [1 – (300/825)] x 100% = 64%

Generation of Electricity Faraday:     

After discovering that currents can produce magnetic fields, people experimented to see if magnetic fields can produce currents Faraday was trying to produce a current with a magnetic field BUT it was not working A current was produced for a short time when the current producing magnetic field was switched on or off Faraday deduced that it could be the charging magnetic fields that were producing the currents and thus he did a series of experiments to investigate

Experiments: 1) Opening/closing switches  created a momentary current 2) Pushing the coil into the magnetic field or pulling it out  created a momentary current 3) Pushing a bar magnet into the coil or pulling it out  created a momentary current Faraday’s Law of Induction: states how changing magnetic fields through a wire coil results in an electrical current through that coil (induction)  

Electrical generator: process of electrical induction can transform mechanical energy into electrical energy By turning the wire loop (which takes mechanical energy), the magnetic fields passing through the loop changes which generates a current (electrical energy)

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Most of the electricity we use is from a conversion of mechanical energy to electrical energy using a generator The mechanical energy can come from many sources: fossil fuel burning, wind or water

Lesson 4: Energy and the Earth Energy Consumption Energy Consumption per Capita: the amount of energy used per person within a country  Varies from country to country since wealthier countries use more energy per person  20% of the world’s population live in highly developed countries and these countries account for 60% of the world’s energy use

Renewable & Non-Renewable Energy Renewable Energy: sources of energy that can easily be restored (can never be fully consumed) Two Types: 1) Based on solar energy: limited only by the lifetime of the sun and the rate of use does not affect the lifetime of the source:  Direct sunlight  Wind  Hydroelectric  Ocean currents  Ocean thermal  Biomass 2) Not based on solar energy:  Geothermal: can be locally depleted but will renew over time (100s of years)  Tidal: comes from gravitational energy between the Earth and the moon Non-Renewable Energy: sources of energy that cannot be easily restored and will be exhausted within a relatively short time due to exploitation 1) Fossil Fuels: coal, oil, natural gas  Can be all used up on a time scale of about 100s of years  Being produced all the time but on a time scale of 100s of millions of years (way too slow!)

2) Uranium 235  Used for nuclear fission power generation  Could be all used up over several decades if used much more strongly than they are now 3) Geothermal: lifetime of geothermal sites varies from site to site

Fossil Fuel Use 

In highly developed countries, the % of fossil fuel consumption is decreasing BUT this does not mean that the total consumption is decreasing

1) Coal consumption:  In North America & Europe  decline in coal consumption (20% decline in North America since 2007)  In Asia  incline in coal consumption  In Canada: coal is used mostly for generating electricity 2) Oil & Natural Gas Consumption:  In North America  petroleum has plateaued, and natural gas consumption has been increasing  In Canada: oil (petroleum products) are used widely EXCEPT for generating electricity and natural gas are also used in most sectors EXCEPT in transportation

Fossil Fuel Trends   

Overall consumption is increasing Almost all countries are at least 50% dependent on fossil fuels BUT the amount varies by region and type of fuel Overall, the consumption of petroleum (oil), coal & natural gas are on the rise (with the exception of very recent past for coal)

Alternative & Nuclear Energy Clean Energy: non-carbohydrate energy that does NOT produce carbon dioxide when generated  It includes hydropower & nuclear, geothermal and solar power  Becoming a popular and strong link between country’s income and use of alternative energy

Canada      

Vast majority of renewable energy produced in Canada = hydroelectricity production (55%) Wind and solar are also used for production of electricity in Canada Biomass use = dominated by wood burning by the pulp and paper industry Canada’s main energy consumption = fossil fuel A percentage increase is projected in natural gas, wind and solar A percentage decrease is projected in nuclear, coal (BIG CHANGE) and hydro (small change)

Lesson 5: Fossil Fuels Types of Fossil Fuels 1) Coal: a black, combustible solid composed mainly of carbon, water and trace elements found in the Earth’s crust; formed from ancient plants that lived millions of years ago 2) Oil: a thick, yellow to black, flammable liquid hydrocarbon mixture found in the Earth’s crust; formed from the remains of ancient microscopic aquatic organisms 3) Natural Gas: a mixture of energy-rich gaseous hydrocarbons (primarily methane) that occurs, often with oil deposits, in Earth’s crust

Fossil Fuel 101 (Video) Fossil Fuel: a group of energy sources that were formed when ancient plants and organisms were subject to intense heat and pressure over millions of years (known as non-renewable because they take this long to be produced)   

Depends on organic matter, temperature, time and pressure conditions Applications: electricity production, transport fuels and can be used to make variety of common products such as plastics, cosmetics and medicines Concerns: safety issues (human health), environmental issues, high cost and highest emitters of CO2 (a greenhouse gas that causes climate change)

Coals Coal Reserves:    

Most abundant fossil fuels Mostly in Northern Hemisphere World’s known resources could last about 200 years at current rate of consumption There is much more coal in resources that are too expensive to access (e.g. kilometres underground)

Coal Mining: Two Types: 1) Surface: used for shallow coal deposits  The soil and rock above the coal deposit (called overburden) are removed  The exposed coal is then extracted  Strip mining: long narrow strips ae mined  overburden from one strip is then put into previously mined strip  Open pit mining: digging a giant hole and extracting the coal  overburden is deposited in nearby valley

2) Subsurface: used when deposits are deeper and harder to access

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Series of tunnels and shafts are used to remove the coal underground More expensive and more dangerous for workers Less surface impacts

Safety:   

90,000 American miners died during the 20th century due to accidents in mining Practices today are much safer than early 20th century but there are still some risks In the 1992 Westray Mine Disaster in Nova Scotia: an explosion occurred in an underground coal mine where 26 miners were killed

Mining: Environmental Issues/Impacts:      

Waste rock and mine tailings can result in releases to water and coil Acidic drainage and leaching of metals from mine workers and mine wastes may occur at metal mines where the acidic drainage can cause significant impacts on water quality and aquatic ecosystems Acid mine drainage can cause pollution when sulfuric acid and dissolved materials (lead, arsenic, cadmium) wash from coal and metal mines into nearby lakes and streams Destruction of surface vegetation and wildlife habitat Destructive form of surface mining occurs commonly in Appalachian Mountains of US Removing coal by leveling a mountain: geography of mountain region can change when the coal is removed o Top of the mountain above the coal: scraped off and dumped into adjacent valley o Coal seam is then removed (if another seam lies bellow then process is repeated) o Streams are buried, lakes are created and destroyed, and large amounts of sediments are washed downstream as bare Earth is eroded

Coal Use in Canada:  

In Canada, about 50% of the coal produced is exported to other countries The other half (50%) is used for production of electricity

Oil and Petroleum Products Oil:  

Petroleum = crude oil (stuff you get from the ground) OR petroleum products (a result of refining process) Compared to coal: oil is more versatile, easier to transport and has a cleaner burning

Petroleum Refining: crude oil is separated into variety of products based on boiling points  

After heated, they are separated in a fractionation tower (about 30m tall) The lower the boiling point, the higher the compound rises in the tower

Crude Oil Proved Reserves:

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Proved means that there’s over 90% confidence of oil being there and being recoverable using existing technology Top 3 countries: Venezuela, Saudi Arabia and Canada

Structural Traps:

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These traps form when sedimentary rock strata buckle or fold upward Oil and natural gas seep through porous reservoir rocks (like sandstone) and collect under nonporous layers such as a roof of shale Natural gas accumulates on top of oil, which in turn floats on underground water

Drilling:   

Once an oil reserve is discovered, drilling starts 70% of the oil production = onshore 30% of the oil production = offshore (more expensive and harder to access)

How Long Will the Oil Last? In t...