Chapter 1 Energy and Power Explosions and Energy An explosion occurs when a great deal of stored energy is suddenly converted to heat in a confined space The heat is enough to vaporize the matter turning it into an extremely hot gas This gas has enormous pressure and puts a great force on everything that surrounds it This pushes everything around it out of the way Energy is the ability to do work Or anything that can be turned into heat Heat something that raises the temperature of material as measured by a thermometer Or the microscopic energy of motion of vibrating molecules Amount of Energy Heat energy cannot always be converted back to other forms A Calorie Food Calories not calorie B Kilowatt Hour kWh We buy electricity from the power company in kWh One kWh costs between 5 and 25 cents Wh 1 Calorie 1 kWh 1000 Calories C Joule TNT Versus Chocolate Chip Cookies What makes TNT so useful for destructive purposes is that it can release its energy very The heat is so great that the TNT becomes a gas that expands so quickly that it pushes quickly and shatters surrounding object Power is the rate of energy release CCC s have high energy but the TNT explosion has high power In chocolate chip cookies energy is released more slowly by the process known as metabolism Part of the reason that CC s contain so much energy per gram is because the weight of the air was not counted Gasoline to explode so popular Gasoline releases its energy by combining with oxygen so it must be well mixed with air A fuel injector allows this to happen Internal combustion allows an explosion to push a piston inside of a car down the axis of the car which in turns drives the wheels of the car The high energy per gram in gasoline is the fundamental physics reason why gasoline is The Surprisingly Low Energy In Batteries A battery stores its energy in chemical form It uses its energy to release electrons from atoms They then carry their energy along metal wires and deliver their energy at another place Battery Powered Cars A typical automobile battery is called a lead acid battery because it uses the chemical reaction between lead and sulfuric acid to generate electricity 85 of energy is actually used with batteries when 15 is lost Only 20 is used by gasoline when 80 is lost as heat Lead acid have a retail cost of about a dollar per pound of battery 50 for 50 pounds Electric cars are far more expensive to operate than our standard gasoline cars Some hybrids can convert some of the mechanical motion of the automobile like extra speed when going down a hill back to stored chemical energy in the rechargeable battery Hydrogen versus Gasoline And the Fuel Cell Hydrogen gas has 2 6 times more chemical energy per gram than gasoline Electrolysis Electricity is passed between two terminals through water and hydrogen and oxygen gas are produced at the terminals The main technical difficulty of the hydrogen economy is that hydrogen is not very dense When liquefied it only has a density of only 0 071 grams per cubic centimeter cc a factor of 10 times less than gasoline With that said we find that liquid hydrogen stores only 0 18 times as much energy per cubic centimeter as gasoline Liquid Hydrogen has about 3x more energy per gram and 3x less energy per gallon 1 Kilogram of Hydrogen 1 Gallon of Gasoline Hydrogen Liquid is dangerous to store due to it expands by a factor of a thousand if warmed Compresses gas hydrogen has 6x less energy per gallon compared to gasoline Due to it being so light airplanes might use hydrogen Uranium Versus TNT For the same weight of fuel nuclear reactions release about a million times more energy than do chemical or food reactions Forms of Energy Kinetic Energy The energy of movement Nuclear Energy the energy stored in the forces between parts of the atomic nucleus Stored Energy Compressed energy released when the nucleus is broken Gravitational Energy The energy that an object has at high altitude when it falls this energy is converted to kinetic energy Power the energy used per second It is the rate of energy release Power Energy Time 1 W 1 watt 1 joule per second 1kW 1 kilowatt 1000 joules per second Energy is Conserved Chemical energy is converted to heat energy and kinetic energy Thermodynamics The study of heat First Law of Thermodynamics Energy is never lost Measuring Energy the temperature of water The easiest way to measure energy is to convert it to heat and then see how much it raises Calorie is the energy it takes to raise one kilogram of water one degree Celsius 1 watt hour 1 Calorie Power Common unites are the watt and the horsepower One horse power 0 18 Calorie per second Watts are the most commonly used unit when measuring electric power A typical large power generation station produces electric power at the rate of about one 1 Horse Power 746 W or 1 kilowatt kW gigawatt one billion watts 10 9 watts 1GW Incandescent Bulbs work by using electricity to heat a thin wire inside the bulb It Takes one horse to light you house Horsepower 1 kilowatt Solar energy can be converted to electricity by using silicon solar cells which are crystals that convert sunlight directly to electricity A cheap solar cell can only convert about 15 of the power or about 150 watts per square meter It would 7 kilometers of solar powered land to produce the same amount of energy as a nuclear plant To cover California s peak energy usage it would only take 350 square kilometers of solar cells We would also need energy storage technology maybe batteries compressed air or flywheels Wind Power heated unevenly Wind is generated from solar energy when different parts of the surface of the Earth are Wind turbines can t be spaced too closely due to the turbulence created by taking energy from the wind and reducing its velocity Kinetic Energy Kinetic Energy Equation E mv 2 V must be in meters per second M is in kilograms The energy is in joules To convert energy to Calories divide by 4200 The Kinetic energy is proportional to the object s mass 1 meter per second mps 2 miles per hour mph 1 kilogram kg 2 pounds lb Classical Relativity Switching the point of view between two objects Review Questions 1 Smart rocks are considered Ballistic Missile Defense 2 One watt is equivalent to One joule Second 3 The asteroid that killed the dinosaurs exploded because It got very hot from the impact 4 Kinetic Energy can be measured in Watts 5 Hybrid vehicles run on Electric power and gasoline 6 What is the main reason that hydrogen
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