Klaynos Posted June 22, 2008 Author Share Posted June 22, 2008 So if the ball was thrown off the back of the train in a direction towards the starting line, and the ball was released at the 100 meter mark away from the starting line, and the ball drops to the tracks on the 100 meter mark, what was its velocity? Relative to what? The tracks? then 0m/s. Link to comment Share on other sites More sharing options...
Motor Daddy Posted June 22, 2008 Share Posted June 22, 2008 Relative to what? The tracks? then 0m/s. So can you please reword the scenario more appropriately, this time stating the real facts? Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted June 22, 2008 Share Posted June 22, 2008 I agree. So why wasn't that stated as the ball's velocity? Because the velocity relative to the train could be greater. I answered using the reference frame of the tracks. So can you please reword the scenario more appropriately, this time stating the real facts? There is nothing incorrect with his original scenario. Link to comment Share on other sites More sharing options...
Motor Daddy Posted June 22, 2008 Share Posted June 22, 2008 Because the velocity relative to the train could be greater. I answered using the reference frame of the tracks. The train's velocity has nothing to do with the ball's velocity towards the starting line. The ball dropped to the tracks, and had a zero velocity. A velocity requires time, and a point of release has no time. You are measuring the ball's velocity from a point in space, not the train. What happens if the train accelerated after the ball was released, does that change the velocity of the ball? No! Link to comment Share on other sites More sharing options...
Klaynos Posted June 22, 2008 Author Share Posted June 22, 2008 Lets just take a moment to consider relative measurements... I'm on a train an throw a ball forward at 10m/s [relative to myself] To me be ball is moving at 10m/s [this gives the reference frame of the above statement] But compared to the earth the train is moving at 20m/s [reference fame of the earth] So compared to my friend Bill stood at the station I've thrown the ball at 30m/s. So even classically velocity measurements are all relative. One of the things that comes with more advanced physics is the lack of an absolute frame of reference, and another is that velocities don't add in the way they do classically as above. the stuff in [ ] are additions. The train's velocity has nothing to do with the ball's velocity towards the starting line. The ball dropped to the tracks, and had a zero velocity. If you "drop" the ball on a train it carries on moving with the same speed as the train relative to the earth, relative to the train it has a 0 velocity. A velocity requires time, and a point of release has no time. You are measuring the ball's velocity from a point in space, not the train. What happens if the train accelerated after the ball was released, does that change the velocity of the ball? No! Classically you can measure an instantaneous velocity, which is the velocity at that point in time. "A point in space" does not have enough information to be a valid reference frame. Link to comment Share on other sites More sharing options...
Motor Daddy Posted June 22, 2008 Share Posted June 22, 2008 Classically you can measure an instantaneous velocity, which is the velocity at that point in time. "A point in space" does not have enough information to be a valid reference frame. What is an instant? Link to comment Share on other sites More sharing options...
Klaynos Posted June 22, 2008 Author Share Posted June 22, 2008 What is an instant? a moment in time... Really now you're just trolling! Link to comment Share on other sites More sharing options...
Motor Daddy Posted June 22, 2008 Share Posted June 22, 2008 a moment in time... Really now you're just trolling! A moment has a duration, no matter how small. Objects in motion (and all objects are in constant motion in this universe) travel a distance during a duration of time. When you apply a measuring tape you are measuring the distance traveled during that duration. A constant velocity of 10 m/s 1 second=10 meters .5 seconds equals 5 meters .25 seconds equals 2.5 meters .1 second=1 meter .001 seconds=.01 meters and on and on. In the end, the object still travels 10 m/s, and you can divide for eternity and not come to a zero time and zero distance. OR? Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted June 22, 2008 Share Posted June 22, 2008 You clearly aren't familiar with calculus. Link to comment Share on other sites More sharing options...
Klaynos Posted June 22, 2008 Author Share Posted June 22, 2008 A moment has a duration, no matter how small. Objects in motion (and all objects are in constant motion in this universe) travel a distance during a duration of time. When you apply a measuring tape you are measuring the distance traveled during that duration. A constant velocity of 10 m/s 1 second=10 meters .5 seconds equals 5 meters .25 seconds equals 2.5 meters .1 second=1 meter .001 seconds=.01 meters and on and on. In the end, the object still travels 10 m/s, and you can divide for eternity and not come to a zero time and zero distance. OR? It's a concept, not a physical reality. Everything you've said is fine, except you've missed out the fact that everything is moving except in their own rest frame, when they're not moving. They're at rest... On the train you don't measure the distance you've moved you measure the distance the earth has moved relative to you... Link to comment Share on other sites More sharing options...
Motor Daddy Posted June 22, 2008 Share Posted June 22, 2008 You clearly aren't familiar with calculus. Am I incorrect? Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted June 22, 2008 Share Posted June 22, 2008 Yes. If I have an equation describing the motion of an object, such as this: x = 20t I can find the velocity at any point in time by taking its derivative: v = 20 The instantaneous velocity is 20 m/s. http://www.scienceforums.net/forum/showthread.php?t=31921 Link to comment Share on other sites More sharing options...
Motor Daddy Posted June 22, 2008 Share Posted June 22, 2008 It's a concept, not a physical reality. Everything you've said is fine, except you've missed out the fact that everything is moving except in their own rest frame, when they're not moving. They're at rest... On the train you don't measure the distance you've moved you measure the distance the earth has moved relative to you... So a passenger on the train has every right to think he/she is the only object in this universe that isn't moving? Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted June 22, 2008 Share Posted June 22, 2008 Yup. Link to comment Share on other sites More sharing options...
Motor Daddy Posted June 22, 2008 Share Posted June 22, 2008 Yes. If I have an equation describing the motion of an object, such as this: x = 20t I can find the velocity at any point in time by taking its derivative: v = 20 The instantaneous velocity is 20 m/s. http://www.scienceforums.net/forum/showthread.php?t=31921 Again, a zero time equals a zero distance. Yup. They are sadly mistaken. Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted June 22, 2008 Share Posted June 22, 2008 That doesn't stop me. Read the tutorial I linked to and you'll see why it works. (Derivatives work via limits.) And why are they mistaken? Link to comment Share on other sites More sharing options...
Motor Daddy Posted June 22, 2008 Share Posted June 22, 2008 That doesn't stop me. Read the tutorial I linked to and you'll see why it works. (Derivatives work via limits.) And why are they mistaken? Because EVERY OBJECT in this universe is in motion, so no object has the right to say they are the one motionless. That is borderline ... schizophrenic. Link to comment Share on other sites More sharing options...
Klaynos Posted June 22, 2008 Author Share Posted June 22, 2008 They are sadly mistaken. 400 years of physics says you're wrong and they're right... I'm pretty sure I know which one is empirically tested and mathematically sound... Every object that isn't at rest in your rest frame is in motion, but anything at rest in your rest frame is at rest. I'm at rest with my houses rest frame... Or at least I hope that I am... Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted June 22, 2008 Share Posted June 22, 2008 Motor Daddy: You meant megalomaniac, but whatever. Every object is in motion relative to what? Other objects? If I'm flying through space in a solid box with no windows, I have no clue if I'm moving or not. There's no way of telling. So I can consider myself stationary and all the laws of physics will work. Every test I perform inside my box will say I'm stationary. If I put in a window and see the stars moving past I can say that they're moving and I'm stationary. I mean, how can you tell the difference? You can do the math for assuming you're stationary and everything else is moving and you'll find that it works out just fine. Link to comment Share on other sites More sharing options...
YT2095 Posted June 22, 2008 Share Posted June 22, 2008 Because EVERY OBJECT in this universe is in motion, so no object has the right to say they are the one motionless. That is borderline ... schizophrenic. not in it`s own Frame it isn`t moving. and "schizophrenic" as you put it (although MPD would be better) is indeed a good way to consider it Link to comment Share on other sites More sharing options...
ydoaPs Posted June 22, 2008 Share Posted June 22, 2008 It's not zero. It's as close to zero as it can possibly be without being zero. Link to comment Share on other sites More sharing options...
Motor Daddy Posted June 22, 2008 Share Posted June 22, 2008 400 years of physics says you're wrong and they're right... I'm pretty sure I know which one is empirically tested and mathematically sound... Every object that isn't at rest in your rest frame is in motion, but anything at rest in your rest frame is at rest. I'm at rest with my houses rest frame... Or at least I hope that I am... If it's mathematically sound, could you tell me which object is static in this universe? Also, if an instant is possible, and an object travels 10 m/s, could you tell me which d/t the object has no motion or time? Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted June 22, 2008 Share Posted June 22, 2008 If it's mathematically sound, could you tell me which object is static in this universe? Using what reference frame? Also, if an instant is possible, and an object travels 10 m/s, could you tell me which d/t the object has no motion or time? I don't understand the question. Link to comment Share on other sites More sharing options...
Motor Daddy Posted June 22, 2008 Share Posted June 22, 2008 Motor Daddy: You meant megalomaniac, but whatever. Every object is in motion relative to what? Other objects? If I'm flying through space in a solid box with no windows, I have no clue if I'm moving or not. There's no way of telling. So I can consider myself stationary and all the laws of physics will work. Every test I perform inside my box will say I'm stationary. If I put in a window and see the stars moving past I can say that they're moving and I'm stationary. I mean, how can you tell the difference? You can do the math for assuming you're stationary and everything else is moving and you'll find that it works out just fine. Let me get this straight. You know you are in motion flying though space in a box, and yet you have no clue if you are in motion or not, and so, by default, you automatically assume you are stationary? I'm having a hard time grasping that concept. Link to comment Share on other sites More sharing options...
Klaynos Posted June 22, 2008 Author Share Posted June 22, 2008 We've got to use more correct definitions if we're going to talk about this in great depth and I think we'll get out of your maths level quite quickly... Velocity in 1D for example is defined as: [math]v= \frac {dx}{dt}[/math] Link to comment Share on other sites More sharing options...
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