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System: Total Momentum

v. v. v. v. v. System: Total Momentum. System. m 2 = 2 kg. m 1 = 0.5 kg. Find total momentum of the system:. +4 m/s. -1 m/s. 2 kg m/s C) 4 kg m/s 3 kg m/s D) 0 kg m/s. 1. Impulse = Change in Momentum. 2. F D t = Change in momentum. 3. If F = 0, momentum does not change.

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System: Total Momentum

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  1. v v v v v System: Total Momentum System

  2. m2 = 2 kg m1 = 0.5 kg Find total momentum of the system: +4 m/s -1 m/s • 2 kg m/s C) 4 kg m/s • 3 kg m/s D) 0 kg m/s

  3. 1. Impulse = Change in Momentum 2. FDt = Change in momentum 3. If F = 0, momentum does not change. “Conservation” of momentum.

  4. +4 m/s -1 m/s How does momentum of the system change after they collide? No external forces. • Positive change in momentum • Negative change in momentum • Zero change in momentum

  5. mA VA’ mA VA VB collide! VB’ mB Conservation of Momentum mB Total mv Before = Total mv After (if no external force on the system)

  6. Be careful with positive and negative signs! Negative Positive

  7. m2 = 2 kg m1 = 0.5 kg Example: Using momentum conservation -3 m/s +4 m/s ? 0 m/s

  8. Momentum conserved even if many particles are involved. Total momentum before explosion = Total momentum after explosion http://www.tutorialwiz.com/explosion/images/f.jpg

  9. Before mvtot = 0 http://www.biology.ualberta.ca/courses.hp/zool250/animations/Squid.swf Squid Propulsion (Explosion) After (mv)water = (mv)squid Total momentum = 0

  10. Recoil: Total Momentum = 0 After Before vrecoil vbullet (mv)bullet + gun = 0 -mgunvrecoil + (mv)b = 0

  11. Elastic collision: Bounces Momentum is Conserved & No Energy "lost" Momentum is always conserved if no external forces are applied to the system!

  12. Inelastic collision: Stick Momentum is Conserved but Energy is not

  13. Bouncy ball (elastic) V1 = -V V2 = V Calculate change in momentum for each. Dead ball (inelastic) V1 = -V V2 = 0

  14. v/2 Inelastic v = 0 v v v v m m m m Elastic v v m m Low Friction Carts on Track Before After Inelastic v m m(at rest)

  15. v2 v2 v1 v2 v1 v2 v1 m m Low Friction Carts on Track Before After Elastic v1 m m Before After Elastic

  16. Lab: Conservation of Momentum Purpose: Experimentally (and mathematically) prove conservation of momentum in a collision or an explosion.

  17. Lab: Conservation of Momentum Procedure:Develop and perform an experiment to prove conservation of momentum. Results should show: momentum before an event = momentum after an event. within  10%.

  18. Things to consider: Explosion, elastic collision or inelastic collision? Will masses stay constant throughout the event? What materials will give good data? What measurement tools will you use? How to measurevelocities and masses before and after the event?

  19. Before beginning the experiment: Write down anticipated procedure and a materials list, then get materials. Do preliminary experiments to make sure your technique will work. Think through equations to make sure to measure and record correct data. Make a data table to use during experiment. Get teacher initials on prep sheet, before starting the experiment.

  20. v’ m v M M v≈0 Momentum Conservation/Transfer • Impulse on basketball and tennis ball (m+M)vbefore  mvafter Actually, the floor provides an external force and this illustrates energy conservation.

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