Transcript Slide 1
8 Momentum Lectures by James L. Pazun 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 don’t 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 Copyright © 2012 Pearson Education, Inc. publishing as Addison-Wesley