Momentum and Energy Chapter 3 Click for 9 page to print Momentum Momentum is inertia in motion Mass x velocity y Has both magnitude and direction Large mass or high p can g give object j speed great amount of momentum Momentum m m v v Change momentum by changing mass or velocity velocity usually usually velocity What causes changes in velocity Force Time is also important p Momentum and Impulse Apply force over time to change velocity and momentum Greater time of application application greater change in momentum Force F x time ti interval i t l is i IMPULSE Impulse F F tt Force x time interval Impulse changes momentum Technically Ft mv Realistically Ft m v Impulse Increasing Momentum Ft m v Pushing a child on a swing the g force Increases momentum Longer push increases momentum more than a short one Ft mv http www bcm edu oto research cochlea Volta 16 html Impulse Decreasing Momentum Stopping pp g the out of control car Change momentum to zero Less force if time is greater Ft m v Impulse Changes Momentum Can change force by changing time Move M away iincreases titime reduces d fforce Toward decreases time increases force Bounce increases impulse There is a change in velocity direction making a greater v So greater force is required Water changes direction has greater i impulse l than h a flflat paddle Ft m v Conservation of Momentum The system the cannon and the ball When it fires fires momentum is conserved conserved they both have momentum in opposite directions Momentum m v Conservation of Momentum No net force No net momentum Momentum m v Conservation of Momentum In the absence of external force force the momentum of the system remains unchanged Momentum m v Consider individual balls as individual systems momentum of each does change Conservation of Momentum Net momentum is the same before the collision As after the collision Momentum M t m v Conservation of Momentum a Y Yellow ll b ballll starts t t stationary t ti b Both balls moving opposite directions c Green ball moving faster Momentum m v Energy Property of a system that enables it to do work Potential Energy Springs Chemicals Ch i l Gravity Kinetic Energy Potential Energy http www howstuffworks com inside clock htm http www himalayan pdx edu virtualjourney slideshow se photos web pages Boy 20with 20Slingshot 2C 20J htm Potential Energy Fuel is chemical potential energy http www alternativefuels com au Biodiesel dragster htm http www lilligren com Redneck redneck lawnmower htm Work is Energy Lift heavy ram of pile driver Work transfers energy to lift into gravitational potential energy Gravitational potential energy Due to object object s s position Relative to a surface weight x height mgh Work done for object to gain potential energy Gravitational potential energy Gravitational potential energy EP mass x acceleration of gravity x height Height H i ht iis above b some reference f llevell Potential energy is always referenced to a zero level defined in the system Gravitational potential energy EP mgh mg weight h height Gravitational potential energy EP mgh Path to the height is not factor in EP Horizontal distance is not factor in EP Kinetic Energy of Motion 1 EK mv2 2 Work is a change in kinetic energy W EK Delta change Kinetic Energy of Motion Heat Sound Electricity El t i it and d lilight ht Kinetic Energy of Motion W EK Work is change in kinetic energy Work energy theorem Net work force x distance W Fd Due to net force mv EK 2 2 mv Fd 2 2 Conservation of Energy Cannot be created or destroyed Can be converted from one form to another Kinetic energy and momentum Properties of moving things Momentum is a vector quantity can be b cancelled ll d with ith opposite it momentum t Kinetic Energy is a scalar quantity Cannot ever be cancelled http www littletheatre net Firecracker Miss miss firecracker contest htm Conservation of Energy Transformation from one form to another Potential energy of stretched rubber of slingshot Transformed to ki ti energy off rockk kinetic flying through air Conservation of Energy Rock transfers its kinetic energy to the object it hits May be transformed to heat upon impact Energy cannot be created t d or destroyed d t d Conservation of Energy http science howstuffworks com roller coaster htm Conservation of Energy EP 10000 J EK 0 J EP 7500 J EK 2500 J EP 5000 J EK 5000 J EP 2500 J EK 7500 J EP 0 J EK 10000 J Conservation of Energy Does a car use more energy when its lights are on What about when the air conditioner is on How about using g the radio when the engine is off Work Transference of Energy Work Force x distance W Fd Work o into to syste system work o out o of syste system Work Lifting load against the force of the weight of the object Move an object twice as far results in twice the work Move two object Twice the weight the same distance as one is twice the work Nothing about time in definition Slow or fast Same force force same distance same work Work Twice the weight Twice the distance W Fd W Fd Work W Fd W Fd Units of work are Newton meters Newton meters same as Joules 2 kg m kg m F d N m m J 2 2 s s SO Work is energy Work is Energy Same units Work occurs with transfer of energy Work W k occurs when h you store t potential t ti l energy Work is Energy Mechanical energy M i thi Moving things has h ttwo forms f 1 Potential mechanical energy Waiting g to work 2 Kinetic mechanical energy Work being done Work is Energy Energy stored in bow Work is done to create the potential energy Power Work done over time Work done Power ti interval time i t l kkg m watt 3 s 2 Units Power energy P time Half the time Twice the power Twice the time Half the power Power P energy time Fuel burn Biodiesel http www alternativefuels com au Biodiesel dragster htm http www lilligren com Redneck redneck lawnmower htm Work Energy and Power Water b hi d th behind the dam Potential energy gy Convert it to electrical energy Work and Energy EP transformed to another form of energy Kinetic energy of motion
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