But in that case, he can't possibly be above 12 years of age.
This concept would be very clear by the time one reaches 12.
The Motor Boat
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But in that case, he can't possibly be above 12 years of age.
This concept would be very clear by the time one reaches 12.
Neddy Bate
Valued Senior Member
But in that case, he can't possibly be above 12 years of age.
This concept would be very clear by the time one reaches 12.
But most twelve-year-olds don't have their own theory.
Speed of the boat relative to the bank (70.4375 m / 22.5 sec) = speed of the water relative to the bank (20.4375 m / 22.5 s) + speed of the boat relative to the water (50 m / 22.5 s)
Now you see your error in posts #79 and #81:
Motor Daddy said:
Motor Daddy said:
I think Pete covered this but for some reason you went off the chain. I think folks are torn between wanting to help you understand basic science concepts and gigging you for trolling.
Two more things:
1. Things are not relative in motion to other chosen things - they are relative to all things, regardless of your choice. You can choose a frame of reference (as long as it's an actual reference frame - space is not). To test this, you will notice the only way you can get an actual coordinate in "outer space" is to measure it from an actual object, such as Earth.
2. The expression v[sub]a wrto c[/sub] = v[sub]a wrto b[/sub] + v[sub]b wrto c[/sub] (v is velocity in the same direction) can be regarded as a transformation of the simplest kind, more commonly called linear translation. In this case linear refers to straight-line movement (no turns or orbits, etc.) It's not clear if that's what you meant by linear transformation. The most general form for that is y = mx + b. Here, m=1, so we have the simplest case: y = x + b. (Speed of the boat wrto the bank = speed of the boat wrto the water + speed of the water wrto the bank).
Both (1) and (2) are logically necessary in order for your statement (quoted at the top of this post) to be true.
Motor Daddy:
Ok.
So, you agree that the speed of the boat in the preferred frame (space) was 70.4375/22.5 = 3.13 m/s = 11.27 km/hr, right?
And you agree that the speed of the boat in the pool was 50/22.5 = 2.22 m/s = 8 km/hr, right?
Do you agree that the pool was travelling at 3.27 km/hr in the preferred frame (space)?
If so, can you explain why 8 + 3.27 = 11.27 km/hr?
Apparently, this seems to be implying that to get the speed of the boat relative to space, we can simply add the speed of the boat relative to the pool to the speed of the pool relative to space.
Can we do that?
If not, why this amazing coincidence?
Motor Daddy said:
Pete said:
Motor Daddy said:
Ok.
So, you agree that the speed of the boat in the preferred frame (space) was 70.4375/22.5 = 3.13 m/s = 11.27 km/hr, right?
And you agree that the speed of the boat in the pool was 50/22.5 = 2.22 m/s = 8 km/hr, right?
Do you agree that the pool was travelling at 3.27 km/hr in the preferred frame (space)?
If so, can you explain why 8 + 3.27 = 11.27 km/hr?
Apparently, this seems to be implying that to get the speed of the boat relative to space, we can simply add the speed of the boat relative to the pool to the speed of the pool relative to space.
Can we do that?
If not, why this amazing coincidence?
Motor Daddy
Valued Senior Member
Right.
Right.
Yes.
Code:
T=0
Little boat .
Pool ..................................................
Cruise ship ....................................................................................................
Harbor .........................................................................................................................
T=22.5
Little boat .
Pool ..................................................
Cruise ship ....................................................................................................
Harbor .........................................................................................................................
What if the harbor was in motion too, say, like the earth is in motion in space?
T=22.5
Little boat .
Pool ..................................................
Cruise ship ....................................................................................................
Harbor .........................................................................................................................
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Neddy Bate
Valued Senior Member
Motor Daddy,
Would this be a good diagram for a boat in river water which is flowing at a constant speed over the river bed?
Would this be a good diagram for a boat in river water which is flowing at a constant speed over the river bed?
Code:
T=0
Boat .
River water ..................................................
River bed .........................................................................................................
T=22.5
Boat .
River water ..................................................
River bed .........................................................................................................Motor Daddy:
Do you now agree that 11.27 = 8 + 3.27 then? That is:
$$v_{boat \rightarrow space} = v_{boat \rightarrow pool} + v_{pool \rightarrow space}$$
The notation $$v_{A\rightarrow B}$$ here means "velocity of A relative to B", by the way.
If you agree with the above equation (which it seems, superficially, that you do), then tell me why this is wrong:
$$v_{boat\rightarrow space} = v_{boat\rightarrow river} + v_{river\rightarrow space}$$
Once you've done that, could you also explain to me why we can't do this:
$$v_{boat\rightarrow embankment} = v_{boat\rightarrow river} + v_{river\rightarrow embankment}$$
Or can we?
What if the embankment is moving relative to space? Does that matter?
And once we've covered all that, please explain to me why my solution to the problem at the start of this thread is wrong.
Do you now agree that 11.27 = 8 + 3.27 then? That is:
$$v_{boat \rightarrow space} = v_{boat \rightarrow pool} + v_{pool \rightarrow space}$$
The notation $$v_{A\rightarrow B}$$ here means "velocity of A relative to B", by the way.
If you agree with the above equation (which it seems, superficially, that you do), then tell me why this is wrong:
$$v_{boat\rightarrow space} = v_{boat\rightarrow river} + v_{river\rightarrow space}$$
Once you've done that, could you also explain to me why we can't do this:
$$v_{boat\rightarrow embankment} = v_{boat\rightarrow river} + v_{river\rightarrow embankment}$$
Or can we?
What if the embankment is moving relative to space? Does that matter?
And once we've covered all that, please explain to me why my solution to the problem at the start of this thread is wrong.
Motor Daddy
Valued Senior Member
Yes, as long as it's known that the river bed is at a zero velocity in space.
Motor Daddy
Valued Senior Member
I agree in this case that the boat had an absolute velocity in space of 11.27km/hr, but you have no way of knowing the velocity of the pool in space. I know that, you don't. I have a preferred frame, you don't, remember?
I know the velocity of the river in space, but you don't. All you know is that the river flows compared to the embankment, but you DON'T KNOW, or have any means available to you to determine the embankment's velocity in space. You never acknowledge the embankment can travel in space because you ASSUME the embankment is always at rest.
Again, what is the velocity of the embankment and how do you determine that velocity? In my world the embankment can move, but in your world it can't.
In my world I know the embankment velocity and in your world the embankment never has a velocity.
Because the speed of the boat in CURRENT is not linear to the speed that the boat traveled in still water.
Doesn't answer his question. It doesn't show why he's wrong.
Still doesn't answer his question. Just sidestepping it.
He asked "Does it matter?" So yes or no? Not answering the question.
That makes a whole lot of sense.
Motor Daddy
Valued Senior Member
James, I have a question for you:
If you are swimming in a pool on a cruise ship that is traveling in a harbor at a substantial speed, and the harbor is at rest in space, is it harder for you to swim in one direction vs the other? Do you feel more force on your arms swimming in one direction vs the other when you are rotating your arms at the same rate each direction of travel? Can you feel the difference when swimming in each direction?
If you are swimming in a pool on a cruise ship that is traveling in a harbor at a substantial speed, and the harbor is at rest in space, is it harder for you to swim in one direction vs the other? Do you feel more force on your arms swimming in one direction vs the other when you are rotating your arms at the same rate each direction of travel? Can you feel the difference when swimming in each direction?
Why is this question going towards the Relative velocity part?
According to the person in the boat,boat is at rest.
According to the person outside,if x is the speed of the current,then speed in one part of the trip is y-x and the other part of the trip is y+x if y represents speed of the boat
According to the person in the boat,boat is at rest.
According to the person outside,if x is the speed of the current,then speed in one part of the trip is y-x and the other part of the trip is y+x if y represents speed of the boat
I'm glad you asked this question; it gets right to the heart of why your arguments are so baffling. The answer is clearly "No."
At least they don't go around trolling forums with it.
You make the most elementary misconceptions. Perhaps you have acalculia?
Motor Daddy:
In the question with the ship and the pool and the little boat, we don't care about the boat's velocity in space. We only want the boat's velocity relative to the land or water that the ship is moving in.
In fact, there's no problem in which the velocity of "space" ever needs to be known.
To answer the problem in the opening post of this thread, I don't need to know the river's velocity in space. I only need to know its velocity relative to the embankment. And the embankment's velocity in space is irrelevant to that.
No. The embankment can do whatever it damn well likes in space. All I care about is the speed the river is flowing relative to the embankment. That's all the problem asks for.
Sure it can, and it does. The earth is moving through space, isn't it? But that doesn't affect anything in the problem.
See above.
I have no idea what you mean by "linear" in that sentence.
So what's your solution to the problem of the current?
Is the problem unsolvable, in your opinion? Is there no way to know how fast a river is flowing from the kind of information given in the problem statement, according to you?
I must say, Motor Daddy, your physics doesn't seem to be very useful for anything. You can't solve problems with it. You can't find this invisible, undetectable "space" you insist on having. You don't know the speed of anything relative to that "space". Your theoretical answers for light don't match real-world experimental results. You can't predict anything. So, what has your theory got going for it?
I have no idea what would happen in your imaginary world of Motor Daddy physics, with your imaginary "space". I can only say what happens in real-world pools on real-world ships - ones that travel in real-world harbors that are not stationary relative to any "preferred frame". In those real-world situations, you don't feel any more or less force on your arms regardless of the direction you swim, as long as the ship keeps moving at constant velocity. This is because the laws of physics are the same in all inertial reference frames. In other words, Einstein's relativity once again correctly predicts real-world observations.
Going back to the boat-in-the-flowing-river example, by the way, the motor wouldn't encounter any more resistance going upstream compared to going downstream. At full throttle, it would produce the same 8 km/hr speed relative to the water, upstream and downstream, regardless of the flow rate of the river relative to the embankment.
In the question with the ship and the pool and the little boat, we don't care about the boat's velocity in space. We only want the boat's velocity relative to the land or water that the ship is moving in.
In fact, there's no problem in which the velocity of "space" ever needs to be known.
To answer the problem in the opening post of this thread, I don't need to know the river's velocity in space. I only need to know its velocity relative to the embankment. And the embankment's velocity in space is irrelevant to that.
No. The embankment can do whatever it damn well likes in space. All I care about is the speed the river is flowing relative to the embankment. That's all the problem asks for.
Sure it can, and it does. The earth is moving through space, isn't it? But that doesn't affect anything in the problem.
See above.
Motor Daddy said:
I have no idea what you mean by "linear" in that sentence.
So what's your solution to the problem of the current?
Is the problem unsolvable, in your opinion? Is there no way to know how fast a river is flowing from the kind of information given in the problem statement, according to you?
I must say, Motor Daddy, your physics doesn't seem to be very useful for anything. You can't solve problems with it. You can't find this invisible, undetectable "space" you insist on having. You don't know the speed of anything relative to that "space". Your theoretical answers for light don't match real-world experimental results. You can't predict anything. So, what has your theory got going for it?
I have no idea what would happen in your imaginary world of Motor Daddy physics, with your imaginary "space". I can only say what happens in real-world pools on real-world ships - ones that travel in real-world harbors that are not stationary relative to any "preferred frame". In those real-world situations, you don't feel any more or less force on your arms regardless of the direction you swim, as long as the ship keeps moving at constant velocity. This is because the laws of physics are the same in all inertial reference frames. In other words, Einstein's relativity once again correctly predicts real-world observations.
Going back to the boat-in-the-flowing-river example, by the way, the motor wouldn't encounter any more resistance going upstream compared to going downstream. At full throttle, it would produce the same 8 km/hr speed relative to the water, upstream and downstream, regardless of the flow rate of the river relative to the embankment.
Motor Daddy
Valued Senior Member
So I measure the embankment to have a 1,000 m/s velocity in space using light, but that's irrelevant to you, because it never needs to be known. If I send a light signal from one end of the pool where and when the little boat starts traveling, how much time does it take the light to reach the other end of the pool?
I measure the embankment to have a 1,000 m/s velocity and the river is flowing compared to the embankment. I measure the water's motion using light and the water is at a zero velocity in space. Now what?
Me.
Where does RoS and length contraction and time dilation come into play with the little boat? Show me the numbers, James. If I had a man climbing a set of stairs on the cruise ship in the x and z directions while the cruise ship was traveling at speed in the water, would the length be contracted the same in the z direction as it is in the x direction? We've discussed the numbers in my world, now show me the length contracted, time dilated, anti-simultaneity numbers from your world!
So we mark off 8km on the embankment. How much time does it take for the boat to travel to that mark upstream, 1 hr? We then test again going downstream. How much time to get back to the original point on the embankment, 1 hr?
In one hour, the boat moves through 8km of water.Motor Daddy said:
In one hour, the water moves V km past the embankment.
So in one hour, the boat moves 8-V km past the embankment upstream.
Speaking as moderator, Motor Daddy, this is off-topic.
The boat, pool, ship, harbour, embankment, and Earth in this problem are all spinning round the Sun and Galaxy. The motion through space is irrelevant to this thread. If you want to discuss absolute motion, open another thread. It might be best to make it in Pseudoscience, unless you word it very carefully.
Special relativity is also off-topic for this thread. The speed of the boat and the water are low, so we are using Galileo's relativity. If you want to discuss special relativity, make another thread.
Would anyone like to do the actual experiment?
You will need:
A boat (eg http://www.toysrus.com/family/index.jsp?categoryId=2290619), with a full tank or fresh batteries
Some still water with measurable landmarks or distance markers, such as a lake, a pond, or a swimming pool, for measuring the still-water speed.
A straight section of smoothly flowing water with measurable landmarks or distance markers (Might be tricky. The creeks in my town are all only a couple of feet across, which means the flow won't be smooth enough. But there are larger creeks and rivers in driving distance, with nice parks by the banks which should be suitable.) A riverboat race course with distance buoys would be ideal.
A stopwatch
A still day (to reduce air resistance effects)
Notepad and pen
(Optional) A video camera, to show everyone what you did.
The stillwater speed should be averaged over a few trials in the pool.
The speed of the current can be measured by dropping in a stick and timing it over the distance.
A few trials each way should be recorded to get the average upstream and downstream speeds.
Who's in?
You will need:
A boat (eg http://www.toysrus.com/family/index.jsp?categoryId=2290619), with a full tank or fresh batteries
Some still water with measurable landmarks or distance markers, such as a lake, a pond, or a swimming pool, for measuring the still-water speed.
A straight section of smoothly flowing water with measurable landmarks or distance markers (Might be tricky. The creeks in my town are all only a couple of feet across, which means the flow won't be smooth enough. But there are larger creeks and rivers in driving distance, with nice parks by the banks which should be suitable.) A riverboat race course with distance buoys would be ideal.
A stopwatch
A still day (to reduce air resistance effects)
Notepad and pen
(Optional) A video camera, to show everyone what you did.
The stillwater speed should be averaged over a few trials in the pool.
The speed of the current can be measured by dropping in a stick and timing it over the distance.
A few trials each way should be recorded to get the average upstream and downstream speeds.
Who's in?
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