The Motor Boat

Motor Daddy:

Obviously, others have already tried to walk you through this simple problem since I was last here. But I'll add my comments, just for good measure, in the expectation that nothing will sink in with you, as usual.

Right.

That depends on who is doing the measuring. It's completely off topic for this thread, though. We don't need to consider special relativity here - just plain old Galilean/Newtonian relativity, which ought to work even in the Motor Daddy universe - if only you could get your brain around your own theory as well as everybody else here can.

Then you work in the embankment frame, same as you do if the embankment has zero velocity, and you get the same answer as before. The embankment velocity with respect to "space" is completely irrelevant to the stated problem. The stated problem only asks for the speed of the current relative to the embankment.

It doesn't. We don't need Einstein's theory here, since the speeds are so low. We can even use Motor Daddy physics and things will work out just fine. In fact, that's all I did in posting my original solution above. Did you see anything about length contraction or time dilation there? No, because it wasn't needed. Those effects are there, of course, but in this problem they are utterly insignificant. Besides, you're nowhere near equipped to deal with the relativistic corrections in this problem, when you can't even get to first base and solve the thing using your own Galilean theory variant.

The length of what?

You seem to be wanting to go off on irrelevant tangents to avoid looking at the actual problem of this thread. Why?

Just solve the problem in the opening post. Then we can worry about all this extraneous rubbish you want to introduce. You need to walk before you can run.

When there's a current, the boat goes slower upstream than downstream. Do you agree?

Can you then see that it can't possibly take the same time in both directions?

Is this really so hard for you? I mean, all it takes is basic common sense and everyday experience. We're not doing rocket science here.

If you're using a marine speedometer to measure the boat speed in the water, then it can ONLY measure the speed relative to the water. How could it possibly know what a distant embankment is doing, let alone "space"? It's just a little propeller that is pushed around by the water going past (or something of that sort).

It's just like how it's "natural" for your car's speedometer to "pretend" that the road is not moving. How can the car's speedo know anything about the road's motion through "space"? It can't.

I'm sure you believe what your speedo tells you when you're trying to avoid getting a speeding fine, Motor Daddy. But how can you possibly trust it? You don't know how fast your car is going relative to "space", so your speedo is useless. Right?

I have no problem with that. That's what the problem is about. You need to know the boat's speed according to the embankment to solve the problem. Like I showed earlier. And like everybody else has explained to you. 8 + 3.27 = 11.27. Remember?

There was no assumption about the 3.27. That was what we calculated from the given information.

You've lost track of the problem now. Go back to post #1 of this thread and read the problem.

The boat's speed relative to water - whether that water is flowing at 3.27 km/hr or at 1 billion km/hr or zero km/hr - is measured to be 8 km/hr. The problem then asks us to calculate the water's speed relative to the embankment.

Right!

That's why we needed the information about the boat's speed relative to the water as well.

The boat's marine speedometer tells us! It is 8 km/hr.

Just look at it! A wonder of modern engineering.

Yes there is. I just saw it on the speedometer reading as the boat was travelling up the river.

Why? 8 + 3.27 = 11.27, doesn't it?

Relative to the embankment, yes.

What else would you expect?[/quote]