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Chapter C13

Chapter C13. Angular Momentum C13B.1, B.2, S.2 Due Wednesday. Monday – Review and problems Tuesday lab = conservation of angular momentum Wednesday - review Friday - Test over chapters C1-C14. Asteroid impacts (left over from chapter 12).

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Chapter C13

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  1. Chapter C13 Angular Momentum C13B.1, B.2, S.2 Due Wednesday

  2. Monday – Review and problems • Tuesday lab = conservation of angular momentum • Wednesday - review • Friday - Test over chapters C1-C14

  3. Asteroid impacts (left over from chapter 12) • The asteroid we think hit the Caribbean 65 million years ago and caused the extinction of the dinosaurs. • Diameter of asteroid ~10 km • Diameter of crater = 175 km • Mass = 1015 kg • Velocity = 20 km/sec = 20,000 m/s. • K.E. = ½mv2= 2 x 1023 j • An atomic bomb = 4 x 1014 j

  4. The atmosphere does not slow the asteroid at all. • Immediately after impact the ejected material enters the hole punched in the atmosphere and the light produced is so bright it immediately ignites all material within 1000 miles. • The whole Earth is showered with vaporized rock emitting a power 5 times that of the sun (catches many other things on fire.)

  5. Holding rotating weights • Is something conserved? • Is that something Krot=½Iω ω2? • If Krot were conserved as the moment of inertia I increased, ω must decrease • When measurements are made we find

  6. Angular Momentum • Angular Momentum =L= Iω • Note that this is similar to linear momentum if I is m and ω is velocity. • Linear momentum = mv • So the conservation of angular momentum then becomes:

  7. Other ways to write This is called a cross or a vector product.

  8. Cross products The direction of r is perpendicular to the plane containing u and w and in a direction given by the right hand rule.

  9. Cross product A=20 B=35 θ = 70º A θ B Find AxB. = 658 What is the direction of AxB? What is the direction of BxA?

  10. Cross product Put on formula sheet. Find C = A x B C = -31i-14j+5k

  11. Differences between dot and cross products of two vectors • Dot or scalar product • Answer is a scalar • A∙B=ABcosθ • Cross or vector product • Answer is a vector • Vector is perpendicular to A and B • A x B=ABsinθ • Direction is given by the right hand rule.

  12. Problems due Wednesday • C13B.1, B.2, S.2 • Due Wednesday

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