Motor Daddy Posted June 21, 2008 Posted June 21, 2008 (edited) Assuming zero acceleration, 1 second. Good, I agree, It takes one second for the train to travel 20 meters when the train's velocity is 20m/s, and the train neither increases or decreases velocity (zero acceleration while traveling the 20 meters) Q: How long does it take the train to travel to the 200 meter mark under the same conditions, when the train passes the same starting line as before, but this time the timer doesn't stop until the train reaches the 200 meter mark on the tracks? Edited June 21, 2008 by Motor Daddy
Motor Daddy Posted June 21, 2008 Posted June 21, 2008 Assuming zero acceleration, 10 seconds. Good, I agree. Q: How far does a person sitting in the train travel during those 10 seconds if the person remains seated the entire duration?
Edtharan Posted June 21, 2008 Posted June 21, 2008 Please provide a quote of mine that disagrees with the notion of relative motion. Here: But you gave the ball's initial velocity of 20m/s. In order for the ball to have a velocity of 10 m/s when the guy throws it, he must have thrown the ball in the opposite direction of the train's travel. In other words, the guy would have had to "decelerate" the ball from 20m/s to 10m/s in order for the ball to have a velocity of 10 m/s. The only way the guy can do that is to throw the ball in the opposite direction of travel of the train's 20 m/s. Basically, the guy is reducing the ball's velocity from 20 m/s to 10 m/s when he "accelerates" the ball in the opposite direction of travel of the ball's initial velocity. The post you were talking about was stating that the ball was travelling at 10m/s relative to the people in the train. But you insisted that the ball was really travelling at 30m/s, or was travelling backwards through the train. You are saying that the ball has an absolute speed, but we are saying that there is no absolute speed of that ball. It is perfectly realistic for that ball to be travelling both at 10m/s relative to the people in the train and at the same time be travelling at 30m/s relative to the people on the platform. Which brings me to this: The train travels 20m/s from a specific reference point. If you want to talk about a different reference point you need to change the 20m/s to the appropriate velocity, as it is no longer valid from a different frame of reference. You were claiming that we changed what we were comparing the speed to in the middle of the discussion. However, what you seem to have misunderstood was that we didn't change the speed of the ball, we just looked at the exact same situation from a different frame of reference. Under relativity, this doesn't actually change anything about the situation. Changing the frame of reference, so long as you follow the maths and science, will not change the result of the situation. So changing the reference point like they did was not wrong. Your objection to it however was. Changing the reference point like that does not invalidate the velocity. It only gives a velocity relative to the new frame of reference. What is important is that the new reference frame will be mathematically linked by the theory of relativity to the other reference points. For instance, if we know that a person on the platform is not moving relative to the platform, then any speed a train has moving past that platform will be the same as the relative frame of reference as the platform its self. But, if the person is moving relative to the platform, then we have to apply the translation between the platform and the person to the difference between the platform and the train if we want to compute the difference in reference frames between the train and the person. Also if we know the differences in the reference frame sbetween the train and a second train, we can use that information to compute the difference between the reference frames of the second train and the platform, even if we don't make a direct measurement between the second train and the platform. We can know our mathematics and scientific theories of this situation are correct if we then make a direct measurement between the second train and the platform. Under Newtonian (classical) mechanics this does not give us the correct answer. When discrepancies of this nature were discovered a new theory was put forward: Relativity. Now, when we do these kinds of computations and test them with direct measurements we now get the correct answers! So no matter how much hand waving you do here, you are not going to show that the direct measurements taken do not match what is predicted by relativity. Simply because the calculations have been made,the experiments have been done and they do match. It may fly in the face of common sense, it may not be understandable by you, but the reality is that this is actually what is happening. If something disagrees with reality, then I will put my money on reality.
Motor Daddy Posted June 21, 2008 Posted June 21, 2008 I'd like to stay on track with the Q&A session for the moment. The question is: Q: How far does a person sitting in the train travel during those 10 seconds if the person remains seated the entire duration?
YT2095 Posted June 21, 2008 Posted June 21, 2008 same distance, 200m, relative to an outside observer (no distance relative to the train). Now... if you`re going to Make a point I suggest you do it ASAP and drop this nonsense!
Motor Daddy Posted June 21, 2008 Posted June 21, 2008 same distance, 200m. Now... if you`re going to Make a point I suggest you do it ASAP and drop this nonsense! I agree, the person travels 200 meters during those ten seconds while sitting in his seat the entire duration. Q: What is the person's velocity if he traveled 200 meters in 10 seconds?
Sayonara Posted June 21, 2008 Posted June 21, 2008 YT, I suggest we stick to "relative to the tracks", since an outside observer could, for all we know, be flying overhead in a fighter jet. A person seated on a train which travels 200m in 10 seconds has a velocity of 20m/s relative to the tracks.
Motor Daddy Posted June 21, 2008 Posted June 21, 2008 YT, I suggest we stick to "relative to the tracks", since an outside observer could, for all we know, be flying overhead in a fighter jet. A person seated on a train which travels 200m in 10 seconds has a velocity of 20m/s relative to the tracks. I agree. So the person and the train have a velocity of 20m/s. Q: Is it correct to say that a ball in the guy's hand (not accelerated) also has a velocity of 20m/s, and that the ball also traveled 200 meters in that 10 seconds?
Sayonara Posted June 21, 2008 Posted June 21, 2008 (edited) If it stays in his hand for the duration, then yes (let's ignore any motion of his hand relative to his body, because that would be uber-pedantry). That is, it has a velocity of 20m/s relative to the tracks. It has a velocity of about 0m/s relative to the man or the carriage. You can see that already, in this simple scenario, we have the same measurement yielding two different but equally correct answers. That reveals a core requirement of relative motion: be explicit in what you are describing. Edited June 21, 2008 by Sayonara³
Motor Daddy Posted June 21, 2008 Posted June 21, 2008 If it stays in his hand for the duration, then yes (let's ignore any motion of his hand relative to his body, because that would be uber-pedantry). Good, I agree. The ball has a 20m/s velocity. Q: If the guy takes the ball to the conductor during the trains trip of 200 meters in 10 seconds (towards the front of the train), which is 10 meters away from where he was sitting at the beginning of the start time, how far does the ball travel during those 10 seconds of the trains travel?
Klaynos Posted June 21, 2008 Author Posted June 21, 2008 Good, I agree. The ball has a 20m/s velocity. Q: If the guy takes the ball to the conductor during the trains trip of 200 meters in 10 seconds (towards the front of the train), which is 10 meters away from where he was sitting at the beginning of the start time, how far does the ball travel during those 10 seconds of the trains travel? In the reference frame of the tracks it is either 210m or 190m, but in the reference frame of the train it is 10m. Note you need to state compared to what you are making the measurements.
Sayonara Posted June 21, 2008 Posted June 21, 2008 Since Motor Daddy is considering the velocity of 20m/s, and not 0m/s, the implication is that the frame being considered is that of the tracks, and not the carriage. MD, if you state which frame/s you are considering as you go, it makes things easier to keep straight in your head. Is the implied frame the one you want to work with?
Motor Daddy Posted June 21, 2008 Posted June 21, 2008 (edited) In the reference frame of the tracks it is either 210m or 190m, but in the reference frame of the train it is 10m. Note you need to state compared to what you are making the measurements. I agree, the ball traveled an additional 10 meters in the direction of travel of the train, so the train traveled 200 meters in 10 seconds, and the ball traveled 210 meters in 10 seconds. Q: If the additional 10 meters the ball traveled during the 10 seconds the train traveled 200 meters was started when the train contacted the start line, and the ball arrived at the conductor at the 10 second mark, what was the velocity of the ball during those 10 seconds (assuming a constant velocity of the ball towards the front of the train for those 10 seconds? Sorry for editing the question, the wording wasn't clear. Edited June 21, 2008 by Motor Daddy
Motor Daddy Posted June 21, 2008 Posted June 21, 2008 Relative to what? The carriage, or the tracks? The ball traveled 210 meters relative to the tracks in 10 seconds.
swansont Posted June 21, 2008 Posted June 21, 2008 The ball traveled 210 meters relative to the tracks in 10 seconds. And your point is ?
Motor Daddy Posted June 21, 2008 Posted June 21, 2008 21m/sec. I agree. Q: Instead of the guy bringing the ball to the conductor who is ten meters towards the front of the train over the course of 10 seconds, what is the velocity of the ball if the conductor brings the guy the ball if he starts to bring the ball back to the guy at the start line, and the ball reaches the guy 10 meters towards the rear of the train (opposite direction of travel of the train) at the finish line 10 seconds later after the starting line?
YT2095 Posted June 21, 2008 Posted June 21, 2008 you`re really over complicating things with your verbosity, the train is moving at 20m/sec, a ball withing that train is moving in the opposite direction at 1 meter a sec. so, relative to the Tracks the ball is moving at 19m/sec. same as it was 210 in the Other direction. can you PLEASE make your Point now!
Motor Daddy Posted June 21, 2008 Posted June 21, 2008 you`re really over complicating things with your verbosity, the train is moving at 20m/sec, a ball withing that train is moving in the opposite direction at 1 meter a sec. so, relative to the Tracks the ball is moving at 19m/sec. same as it was 210 in the Other direction. can you PLEASE make your Point now! I agree, the ball has a velocity of 19 m/s. The ball is NOT moving in the opposite direction at 1 m/s, the ball is continuing to move FORWARD, in the SAME direction of travel of the train, just at a slower rate compared to the train. The train is moving at 20 m/s, and the ball is moving 19 m/s in the same direction.
ydoaPs Posted June 21, 2008 Posted June 21, 2008 Motor Daddy, 19m/s relative to what? I guess you're not going to try my word problem.
Motor Daddy Posted June 21, 2008 Posted June 21, 2008 Motor Daddy, 19m/s relative to what? There is one reference point and that is the starting line.
YT2095 Posted June 21, 2008 Posted June 21, 2008 wrong, it IS moving in the opposite direction within the train! it`s only moving at 19m/sec relative to the Outside (jet fighters excluded). and there IS more than one Ref point!
Motor Daddy Posted June 21, 2008 Posted June 21, 2008 (edited) wrong, it IS moving in the opposite direction within the train! it`s only moving at 19m/sec relative to the Outside (jet fighters excluded). and there IS more than one Ref point! If you use the train as a reference point for the ball's direction of travel, it is not moving, so how could the ball be traveling in the opposite direction of the train if the train is not moving? Edited June 21, 2008 by Motor Daddy
Recommended Posts