# Tag Info

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Why don't we consider the centrifugal force acting on the bob of a pendulum while drawing the Free Body Diagram of a pendulum? It's also a sort of circular motion. First off, you meant centripetal rather than centrifugal. Circular motion requires a centripetal force, not a centrifugal force. There are two forces acting on the pendulum bob: ...

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You got it half right, but you got so focused on the correction factor that you forgot to calculate the trip time in your rest frame. In deference to Bill N, let me rephrase the question, hopefully more to his liking. The astronaut is travelling to a star sixteen light years away which is stationary with respect to earth. During this trip he ages fifteen ...

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So, special relativity says that every frame is as good as any other frame, and there is no absolute frame of reference. All good. And special relativity is experimentally falsified and general relativity uses the word general to cover the case when inertial frames are only local and not global, such as in the universe we live in. Suppose there is ...

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If the velocity of the aether wind is a sizeable fraction of c, the apparent velocity of c will depend strongly and obviously on the direction in which the measurement is taken. Since this is not true, the aether wind velocity must be quite small, which requires a sensitive instrument to detect the effects. It was exactly this range of possible wind speeds ...

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You'll see the object at first accelerate towards the hole (under gravity) and then slow more and more as it approaches the event horizon. It will asympotically freeze in place at the event horizon and then gradually shift redder and redder until it disappears. This is assuming that the black hole is big enough that the acceleration is similar across the ...

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Yes. Under any normal operating mode today, the station rotates at the rate of once per orbit so that a particular part of the station always points at the earth. This is almost identical to the way the moon orbits the earth. But this is not something that has to happen. During assembly, there were times when the station did not rotate. So if there were ...

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The reason these statements are consistent becomes clear if we quote from the Landau & Rumer book a little more extensively: Ahead of us is a very long railway line with Einstein's train moving along it. At a distance of 864,000,000 kilometers from each other there are two stations. At its speed of 240,000 kilometers per second, Einstein's ...

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The classical fluid mechanical idea of a vortex is well illustrated by this picture, which shows a vortex created by the passage of an aircraft wing, revealed by colored smoke. In classical fluid dynamics, a region of mostly rotational fluid around an axis line is known as a vortex. This axis line can be curved or straight, depending on the physical ...

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It's actually not a contradictory result. Each observer sees the other's clock running more slowly. You're tacitly assuming the existence of a third, "absolute" frame wherein times of other frames can be unambiguously compared, which would be a contradiction because it would require duration measurements to be well ordered. However, one of the fundamental ...

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It's pretty natural to think that a star can have velocity - there's no reason a star shouldn't be able to move. The first thing you need to know is "velocity relative to what?" Stars in our galaxy are all in some kind of orbit around the galaxy, so you can talk about velocity in galactic coordinates. Binary stars orbit each other, so you can talk about ...

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Once it goes into orbit, it will remain in the same attitude, what I mean is the cupola the astronauts look out of always looks "down," was far as I know. I don't think the ISS has any spin, so it should stay in the same position. The International Space Station orbits about 354 kilometers (220 miles) above the Earth and travels at approximately  ...

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Conservation and invariance are fundamentally different things. Conservation means "doesn't change with respect to time". While invariance means "doesn't change with respect to Lorentz transformations". Components of four-momentum transform like vector components and are thus NOT invariant under Lorentz Transformations. But that doesn't prevent them from ...

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If the 4-momentum were invariant then it would be a scalar. 4-vectors are defined by the way their components mix when we change coordinates. In particular when we apply a lorentz transformation to our coordinates the inverse transformation is applied to the vector. As a simple example consider what happens to the energy when we boost. If we start in the ...

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Earth is moving around sun in an orbit with mean radius 1AU. Time of one revolution is 1 year . Thus, its speed is $$v \approx 2 \pi \dfrac{1AU}{1year} = 30km/sec$$ . Sun moves s=around galactic center at a speed of $v'=220km/sec$. Thus, when you are standing still on Earth,you can have a velocity of $v'+v$ with respect to center of Milky way galaxy. This ...

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But then I'm assuming the time it takes him for an observer is equal to 16 years, am I correct in doing this? I think not since that means the astronomer would be travelling at the speed of light to an observer... Okay, first thing: an astronaut (Greek, star sailor) is different from an astronomer (Greek, star namer). The former is seen at the wheel of ...

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One approach that uses the matrices you've already derived is to set $L_{bh}=L_{bw}L_{wh}$ and then solve for $\gamma$.

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