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A similar problem with Uranus had led to the discovery of Neptune, so it seemed as if there must be some planet closer to the Sun than Mercury, lost in the Sun’s glare, perturbing its orbit. Gravitation seemed to work, except they couldn’t figure out what was going on with Mercury’s orbit about the Sun. And let’s furthermore imagine that it’s out in space somewhere. Let’s do this in one dimension for simplicity. Not one Germany. Sixty million separate Germanies. One could complain that since we can’t measure the earth’s "rebound" in this case, maybe it isn’t rebounding. But the absence of evidence (i.e., the failure to be able to measure it) isn’t the same as the evidence of absence (i.e., evidence the earth doesn’t actually rebound when the ball hits the bumper). If some bored passenger on the train were to measure the speed of sound (assuming they’d let him climb around on top of the train in the first place), he’d hear the sound move slower, relative to the train, when measured from in front of the whistle, at a normal speed to the side of the whistle, and faster behind the whistle. Trains have a nice source of sound on them, How to Hold a Billiard Cue the whistle (or today the horn).

Thus the sound wave travels the same speed in all direction from the train’s whistle (horn), as heard from someone on the ground on a breezeless day. They hit at the same time. I’ve seen demos of this principle done where steel ball bearings are used, in a special little gizmo that drops one the same time a spring shoots the other one out horizontally. With a rocket the goal is to make the big thing move, and flinging the fuel out as fast as possible is a means to that end. So if we want another 4 m/s, burn another kilogram of fuel and oxidizer, right? Because the rocket burned 1 kg of its own mass to get to this point, and now it masses 999 kg, So another kilogram of fuel, adding 2000 kg•m/s to the rocket’s momentum, will actually add slighly more than 4 m/s, precisely 4000/999 m/s, in fact. So if the rocket burns one kilogram of fuel plus oxidizer, and shoots the combustion product out the nozzle at 4000 m/s, what happens? But the takeaway is that even in following the other formula, the rocket and its burnt fuel are abiding by the conservation of momentum; in fact it relies on it to operate.

The momentum of the rocket fuel after it has been burned is 1kg • -4000m/sec. In fact, in order to make the ball rebound, the momentum of the ball is changing by twice its prior value. The rocket, including the fuel, has a momentum of zero. In the next section, we'll explore the fascinating history of cabin decor styles, including Scandinavian, Appalachian, Western, and many more. Cabin decor is a way to turn your log cabin into a cozy, charming environment. When darkness falls, kerosene lanterns are lighted, and life continues inside the cabin much as it has for almost a century. •m/s. But the earth’s mass is much, much, much more than b, so the velocity imparted by the ball to the earth is microscopic. No one actually does this, but from a bookkeeping standpoint it’s definitely twice as much time with the ledger as conservation of mass is.

4000 kg•m/s. The rocket has a mass of 1000 kg, so that works out to the rocket now moving at 4 m/s in the forward direction. When a crucial vote is taken, all the cast, bar Brandt, gather closely together below moving their chairs forward to hear the important result. Tense up your arm and the entire weight of your body resists the torque and you don’t move much. And in fact they don’t even need to be the same weight. If he were really ignorant of how trains move, he could even prove it wasn’t moving sideways, but rather forward, this way. He could even figure out how fast the train was going by taking the difference between his "in back of" reading and his "in front of" reading and dividing by two. Negative because the rocket is blowing the exhaust out behind it, the nose points in the positive direction, the nozzle points in the negative direction. So how fast is the sound travelling in front of the train, and how fast is it travelling behind the train?