Momentum. Momentum and Energy. Momentum and Impulse. Momentum. Impulse. Impulse Increasing Momentum

Transcription

1 Momentum and Energy Chapter 3, page Review quetion: 1,3,4,7, 8, 11, 1, 14-17, 0, 1 Momentum Momentum i inertia in motion Ma x velocity Ha both magnitude and direction Large ma or high peed can give object great amount of momentum Momentum Change momentum by changing ma or velocity uually velocity What caue change in velocity? Force Time i alo important Momentum and Impule Apply force over time to change velocity and momentum Greater time of application, greater change in momentum Force x time interval i IMPULSE Force x time interval Impule change momentum Impule Ft = Δ(mv) Impule Increaing Momentum Puhing a child on a wing the force Increae momentum Longer puh increae momentum more than a hort one Ft = Δ(mv)

2 Impule Decreaing Momentum Ft = Δ(mv) Stopping the out of control car Change momentum to zero Le force if time i greater Impule Change Momentum Can change force by changing time Move away increae time, reduce force Toward decreae time, increae force Bounce increae impule Ft = Δ(mv) There i a change in velocity to zero, and reveral of the direction So greater force i required Water change direction, ha greater impule than a flat paddle Conervation of Momentum The ytem: the cannon and the ball When it fire, momentum i conerved they both have momentum: in oppoite direction Conervation of Momentum No net force No net momentum Conervation of Momentum In the abence of external force, the momentum of the ytem remain unchanged Conider individual ball a individual ytem: momentum of each doe change

3 Conervation of Momentum Conervation of Momentum Net momentum i the ame before the colliion A after the colliion a. Yellow ball tart tationary b. Both ball moving oppoite direction c. Green ball moving fater Work Work W=Fd Tranference of Energy Work = Force x ditance W=Fd Nothing about time in definition Slow or fat Same force, ame ditance = ame work Work Lifting load againt the force of the weight of the object Twice the ditance reult in twice the work Twice the weight i twice the work Work Twice the weight Twice the ditance W=Fd

4 Work W=Fd Work W=Fd kg m Unit of force : Newton = Unit of work are Joule Work i energy Force x ditance : Newton meter = kg m m = =Joule kg m Work Weight lifter doe work to lift barbell expend energy to keep the potential energy in the barbell But he doe no work on the barbell after it i lifted W=Fd Work v. Energy Same unit Work occur with tranfer of energy Work occur when you tore potential energy Work v. Energy Mechanical energy Moving thing ha two form 1. Potential mechanical energy Waiting to work Energy tored in bow Work i done to create the potential energy Work v. Energy. Kinetic mechanical energy Work being done

5 Work v. Energy Potential Energy Lift heavy ram of pile driver Work tranfer energy to lift into potential gravitational energy Fuel i chemical potential energy Potential Energy Due to object poition Relative to a urface = weight x height = mgh Work done for object to gain potential energy

6 E P = ma x acceleration of gravity x height Height i above ome reference level Potential energy i alway referenced to a zero level defined in the ytem E P = mgh mg = weight h = height E P = mgh Path to the height i not factor in E P E P = mgh Horizontal ditance i not factor in E P Kinetic Energy of Motion 1 E K = mv Work i a change in kinetic energy W = E K Delta change Kinetic Energy of Motion How much further will a car kid if you lock up the wheel at 90 km/h v. 30 km/h? E K = ½ mv ½ ma x (90 km/h) = ½ ma x 8100 km /h ½ ma x (30 km/h) = ½ ma x 900 km /h ½ ma x 8100/ ½ ma x 900 = 9 Nine time further!

7 Kinetic Energy of Motion Heat Sound Electricity and light Work-Energy Theorem Work i change in kinetic energy Work = ΔKE Kinetic Energy of Motion W = E K Work-energy theorem Net work = force x ditance = Fd Due to net force mv E = mv Fd = K Kinetic energy and momentum Propertie of moving thing Momentum i a vector quantity can be cancelled with oppoite momentum Kinetic Energy i a calar quantity Cannot ever be cancelled Cannot be created or detroyed Can be converted from one form to another Tranformation from one form to another Potential energy of tretched rubber of linghot Tranformed to kinetic energy of rock flying through air

8 Kinetic energy of rock flying through air = Potential energy of tretched rubber of linghot Tranformed from potential to kinetic Rock tranfer it kinetic energy to the object it hit May be tranformed to heat upon impact Energy cannot be created or detroyed It may be tranformed from one form into another, but the total amount never change. E P = J E K = 0 J E P = 7500 J E K = 500 J E P = 5000 J E K = 5000 J E P = 500 J E K = 7500 J E P = 0 J E K = J Sun energy from fuion of hydrogen to helium 1 4 H 4 1 He + energy Sun energy converted to chemical energy by plant Sun heat converted to potential energy when it evaporate water

9 Power Doe a car ue more fuel when it light are on? What about when the air conditioner i on? How about uing the radio when the engine i off? Work done over time Power = Work done time interval Power Work W=Fd Power = work / time Unit Joule/econd kg m / = kg m 1 = kg m kg m = watt 3 kg m 3 Power P = energy/time = watt Half the time =Twice the power Twice the time =Half the power Fuel burn Biodieel Power P = energy/time How much work o done to lift a 75 N bowling ball 1 meter? Work = Force x ditance Work = (75 N) (1 m) = 75 J

10 How much work i done on the bowling ball when you carry a 75 N bowling ball acro the room? Not any, no change in height, o no change in potential energy How much power i expended to lift a 75 N bowling ball 1 meter in 1 econd? Power = Work/time Work = 75 J Power = (75 J)/1 = 75 W How much power i expended to lift a 75 N bowling ball 1 meter in 1 minute? Power = Work/time Work = 75 J Power = (75 J)/60 = 1.5 W What i the gravitational potential energy when a 75 N bowling ball ha been lifted 1 meter? E P = mgh mg = weight = 75 N E P = (75 N)(1 m) = 75 J W = (75 N) (1 m) = 75 J Potential energy only important when it change Change of E P doe work W=Fd E P tranformed to another form of energy Water behind the dam Potential energy

11 Machine E P tranformed to another form of energy Kinetic energy of motion Efficiency Source of Energy