Lectures by James L. Pazun 8 Momentum Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Goals for Chapter 8 To study momentum. To understand conservation of momentum. To study momentum changes during collisions. To add time and study impulse. To understand center of mass and how forces act on the c.o.m. To apply momentum to rocket propulsion. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Momentum is a vector quantity. Figure 8.1 Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Momentum can cause injury ( a concussion) This is a frame of reference problem just like a passenger in a car. When the brain and skull are moving at the same velocity, there is no problem. If the skull changes abruptly the brain does not, there is a possibility of an injury. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Analysis of a collision Figure 8.2 Refer to the worked example on page 234. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Momentum is conserved. Figure 8.3 Astronauts provide excellent examples of momentum transfer. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Scoring a strike is many momentum transfers at once. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley An astronaut rescue - Example 8.2 Refer to the worked example on page 237. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Rifle recoil Example 8.3 Refer to the worked example on pages 237 and 238. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Head-on collision Example 8.4 Refer to the worked problem on page 238. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Collisions on a horizontal plane Figure 8.7 Refer to worked example on page 239. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley An explosion considered backward in time Figure 8.8 Refer to the worked example on page 239. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Particles dont separate Figures 8.9 and 8.10 Allows us to draw the distinction between elastic collisions and inelastic collisions. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Sum O momentum? We can even find physics in unexpected places. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Energy in an inelastic collision Figure 8.11 Refer to the worked example on page 241. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley We may do this experiment Figure 8.12 Air tracks allow controlled linear collisions. Refer to worked example on page 241. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley The ballistic pendulum Figure 8.13 Often done with a.22 in lab before firearms were forbidden on campus. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Different masses Figure 8.15 Incoming and outgoing velocities are very mass dependant. Refer to worked example on page 241. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Different masses Figure 8.15 Incoming and outgoing velocities are very mass dependant. Refer to worked example on page 244. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Billiards? Figure 8.16 Different situations depending on the nature of the strike Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley A solved air track problem Figure 8.16 See the example on page 245. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Off center collisions Example 8.11 Difficult is the adjective that comes to mind. Refer to page 247 in your text. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Impulse, duration of the impact Figure 8.21 Again, different situations depending on the nature of the strike Refer to worked example 8.12 Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Everything acts on the center of mass Figure 8.25 Refer to the worked example on page 252. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Rocket propulsion Figure 8.28 Momentum changes themselves are altered as the projectile uses fuel or explodes. Refer to example 8.15