* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Energy - Teacher Notes
Open energy system models wikipedia , lookup
Dark energy wikipedia , lookup
Energy storage wikipedia , lookup
Energy subsidies wikipedia , lookup
100% renewable energy wikipedia , lookup
Low-Income Home Energy Assistance Program wikipedia , lookup
Zero-energy building wikipedia , lookup
Public schemes for energy efficient refurbishment wikipedia , lookup
Low-carbon economy wikipedia , lookup
World energy consumption wikipedia , lookup
Alternative energy wikipedia , lookup
Energy Charter Treaty wikipedia , lookup
Gibbs free energy wikipedia , lookup
International Energy Agency wikipedia , lookup
Energy returned on energy invested wikipedia , lookup
Energy policy of the United Kingdom wikipedia , lookup
Regenerative brake wikipedia , lookup
Energy policy of Finland wikipedia , lookup
Energy harvesting wikipedia , lookup
Distributed generation wikipedia , lookup
Life-cycle greenhouse-gas emissions of energy sources wikipedia , lookup
Energy efficiency in transport wikipedia , lookup
Internal energy wikipedia , lookup
Energy in the United Kingdom wikipedia , lookup
Negawatt power wikipedia , lookup
Energy policy of the European Union wikipedia , lookup
Kinetic energy wikipedia , lookup
Potential energy wikipedia , lookup
Conservation of energy wikipedia , lookup
Energy efficiency in British housing wikipedia , lookup
Energy Independence and Security Act of 2007 wikipedia , lookup
ENERGY Ability to do WORK Measured in Joules (calories or kilocalories) What is Energy? Work depends on: ◦ The amount of force applied to the object. ◦ The distance that the object moves while the force is applied. ◦ The direction of the force with respect to the direction the object moves. What is Work? Work: Work is done on an object whenever a force is exerted on an object through some distance. If the force is constant and parallel to the direction of movement then: W=Fd W = 0, if d = 0 No work done if object doesn’t move. W = 0, if F = 0 No work done, whenever there is no force. If the force on the object is in the direction the object moves, the work done is: W = Fx F x If the direction of the force is opposite the direction the object moves, work is: W = -Fx F x If the force is perpendicular to the direction the object moves, the work done is 0. If the object doesn’t move, the work done is 0. F W=0 x Force is NOT Work How is all energy divided? All Energy Potential Energy Gravitation Potential Energy Elastic Potential Energy Kinetic Energy Chemical Potential Energy What is Potential Energy? o Energy that is stored and waiting to be used later What is Gravitational Potential Energy? Don’t look down, Rover! Good boy! o Potential energy due to an object’s position o P.E. (gravitational) = mass x height x gravity What is Elastic Potential Energy? o Potential energy due compression or expansion of an elastic object. Notice the ball compressing and expanding Work done by a spring = ½ Kx2 What is Chemical Potential Energy? o Potential energy stored within the chemical bonds of an object An object’s kinetic energy depends on: the object’s mass. ◦ Kinetic energy is directly proportional to mass. the object’s speed. o Kinetic energy is directly proportional to the square of the object’s speed. o Energy an object has due to its motion K.E. = ½ mv2 What is Kinetic Energy? Kinetic energy is a scalar quantity. When the kinetic energy of an object changes, work has been done on the object. Work is a scalar quantity. What is the kinetic energy of an object with mass of 1 kg, moving at 1 m/s? 0.5 Joule. The work done on an object by the net force equals the object’s change in kinetic energy. Wnet = DKE Work and Kinetic Energy Law of Conservation of Energy If no external forces act on a system, the total energy of the system will remain constant. Mechanical Energy = PE + KE What are different Forms of Energy/Energy Transformations? Suppose you have to exert a force of 10 Newtons to push a book 1 meter across a horizontal table at constant velocity (as shown above). Since your force is in the direction the book moves, the work you do on the book is given by: Your work = Fx = (10 N)(1 m) = 10 Joules Work done by Friction •The work-energy equation would lead you to think that doing 10 Joules of work on the book should increase the kinetic energy of the book by 10 Joules - but that doesn't happen (the speed of the book is constant). What's going on? •A friction force opposes the motion of the book. This force must also be 10 Newtons (Since the book moves at constant velocity, the net force on it must be zero.). •The friction force pulls in the opposite direction from the direction the book moves, the work done by friction is given by: Work done by friction = -Fx = -(10 N)(1 m) = -10 Joules •This means that the friction force removes 10 Joules of energy from the book. So, while you were adding 10 Joules of energy to the book, friction was busy taking the 10 Joules of energy away from the book. This is why the kinetic energy of the book does not change! Power is the rate work is done. Units of power: 1 Joule/sec = 1 Watt 1000 Watts = 1 kilowatt Power is a scalar quantity. Power = DWork time W P t A machine is a mechanical device used to do work. Examples of simple machines: ◦ Inclined plane ◦ Lever ◦ pulley What are (Simple) Machines? A machine can never output more work (energy) than is put into it. At best, Workout = Workin Workin Machine Workout (Simple) Machines Machines can’t multiply work or energy, but they can multiply force. Mechanical advantage measures how much a machine multiplies force. MA = Force machine exerts Force you exert What is Mechanical Advantage? The efficiency of a machine tells how much of the energy (work) that goes into the machine actually does useful work. It is usually expressed as a percent. Efficiency = Useful work done Energy input x 100% How do we Measure Efficiency?