Simple Nature - Light and Matter

the asteroid’s energy and boosting it into an orbit with a greaterradius. On the other hand, if the asteroid’s spin and orbital motionare in opposite directions, the Yarkovsky push brings the asteroidspiraling in closer to the sun.Calculations show that it takes on the order of 10 7 to 10 8 years forthe Yarkovsky effect to move an asteroid out of the asteroid beltand into the vicinity of earth’s orbit, and this is about the same asthe typical age of a meteorite as estimated by its exposure to cosmicrays. The Yarkovsky effect doesn’t remove all the asteroidsfrom the asteroid belt, because many of them have orbits thatare stabilized by gravitational interactions with Jupiter. However,when collisions occur, the fragments can end up in orbits whichare not stabilized in this way, and they may then end up reachingthe earth due to the Yarkovsky effect. The cosmic-ray techniqueis really telling us how long it has been since the fragment wasbroken out of its parent.Discussion QuestionsA The following is an incorrect explanation of a fact about target shooting:“Shooting a high-powered rifle with a high muzzle velocity is different fromshooting a less powerful gun. With a less powerful gun, you have to aimquite a bit above your target, but with a more powerful one you don’t haveto aim so high because the bullet doesn’t drop as fast.”What is the correct explanation?f / Discussion question A.B You have thrown a rock, and it is flying through the air in an arc. Ifthe earth’s gravitational force on it is always straight down, why doesn’t itjust go straight down once it leaves your hand?C Consider the example of the bullet that is dropped at the samemoment another bullet is fired from a gun. What would the motion of thetwo bullets look like to a jet pilot flying alongside in the same direction asthe shot bullet and at the same horizontal speed?3.4.2 Rotational invarianceThe Cartesian approach requires that we choose x, y, and zaxes. How do we choose them correctly? The answer is that it had190 Chapter 3 Conservation of Momentum