Merged DDWFTTW in a “Real” Wind

[Modified]

That is also true for the cart! One more difference between treadmill and road.

No, it isn't. You have to compare equivalent situations. Someone jumping onto a treadmill moving at 2 mph is equivalent to someone jumping from a vehicle moving at 2 mph onto the ground. Either way requires the same amount of energy (none) to get to 2 mph relative to the surface. Placing the cart on a treadmill moving at 10 mph is equivalent to placing it on the road from a vehicle moving at 10 mph. Either way requires the same amount of energy (none) to get the cart to 10 mph.

 

[69dodge]

Energy is required to overcome the tendency to move with the planet and that energy does not come from the motion of the planet itself. That is unlike a treadmill that we have already agreed can give energy to the cart that is running on it.

I don't follow. Isn't there the same tendency for someone on a treadmill to move with the treadmill, because of the friction between the treadmill and their shoes?

I think it might help if you thought more about the details of how the cart on the treadmill works, instead of simply saying that "we have already agreed" that it works. What are the various forces involved? What pushes on what, in what direction and with what strength? (Force is an easier concept than energy, I think.) Then see if any of the forces would be different on the road in a wind. If they wouldn't be, the cart would work there just as well.

 

[Myriad]

So prof, the engineers who designed this treadmill and wind tunnel facility, and the race car designers who use it to test cars at racing speeds, don't know what they're doing?

http://jalopnik.com/#!252670/haas-builds-rolling-road-wind-tunnel
http://www.windshearinc.com/

Looks like it cost millions of dollars but they didn't have you to tell them that it's completely different from real racing conditions because the car isn't moving with respect to the earth. Fortunately for them, they've been able to fool a number of investors and customers that it works. You'd think after four years of operation someone would notice that the test results from the facility disagree with actual performance on the road, but you know those racing teams who spend millions tweaking every detail of their vehicles' perfomance. They're kind of clueless about basic physics, right?

These silly people are claiming that if you ran the belt at, say, full speed of 180 mph, while setting the air current at also 180 mph, that the result is the same as driving the car 180 mph over the road on a windless day. They'd even probably claim that belt speed of 180 mph with air speed of 160 mph would be just like driving the car at 180 mph on a road with a tail wind of 20 mph. And if they were really silly, they'd claim that a belt speed of 20 mph with the wind tunnel fans turned off would be just like driving the car down the road at 20 mph with a tail wind of 20 mph. But they're engineers using multimillion dollar equipment to test multimillion dollar projects, I'm sure they're easy to fool.

Respectfully,
Myriad

 

[Jack by the hedge]

I don’t know of any examples where the road is a source of energy for vehicles travelling on it. By road I mean that it is part of the planet.

It seems to me your objection is encapsulated here. You are prepared to consider different frames of reference except in any case involving the surface of the planet when you will insist on that as a fixed frame of reference. There is no need to do so. The results work out the same whichever reference frame you choose for convenience.

The world is moving all the time but because of gravity everything including the atmosphere moves with it

Gravity pulls me downwards. It doesn't drag me along sideways with the rotation of the earth. Friction does that. Friction on the surface of a treadmill would do exactly the same.

Although the DDWFTTW cart itself was unintuitive and contentious, all this stuff about the equivalence of inertial frames of reference is absolutely mainstream physics.

 

[jadebox]

Gravity pulls me downwards. It doesn't drag me along sideways with the rotation of the earth. Friction does that. Friction on the surface of a treadmill would do exactly the same.

And momentum .....

If you jump into the air from the surface of the earth, you land back at the same spot. The earth doesn't rotate away under you.

It's the same thing on treadmill ... make a mark on the treadmill and stand on it. Then jump into the air, you'll land right on the mark.

In the examples above, you'd have to do the experiment in a vacuum so that wind doesn't push you and cause you to land in a different spot.

Or, for the earth-based experience jump when there's no wind. On the treadmill, jump when the air is blowing the same speed and direction as the treadmill is moving (which is the equivalent of the "no wind" situation on earth).

-- Roger

 

[humber]

Oh sorry, I didn't know it was a personal message intended only for spork. I am just trying to keep up with the discussion and I did not understand this. Whatever blip means.

You are a snake in the Garden of Eden, so they will assume that you are one of the Devil's disciples, Harold. That is, they are suggesting you are Harold Bricer. Rule: There can only be exactly 3 snakes. Me, Yevgheni and Harold: though many think the latter are the same poster.

 

[tobermoryphil]

Well on the treadmill it certainly takes less effort to get up to speed...

Dave

Please explain why. The comparison is with a road and tailwind. I assume the treadmill starts from rest, as does the runner on the road.

 

[spork]

Get your Harold radar repaired, spork.

Indeed. It sounded like an innocent enough question - but the parallels are becoming increasingly obvious.

 

[humber]

So prof, the engineers who designed this treadmill and wind tunnel facility, and the race car designers who use it to test cars at racing speeds, don't know what they're doing?

http://jalopnik.com/#!252670/haas-builds-rolling-road-wind-tunnel
http://www.windshearinc.com/

Looks like it cost millions of dollars but they didn't have you to tell them that it's completely different from real racing conditions because the car isn't moving with respect to the earth. Fortunately for them, they've been able to fool a number of investors and customers that it works.

And you at the same time for no cost. As I have now pointed out several times, it is a rolling road, in a wind tunnel. The same blunt denial applies to all Carteerian arguments.
The car is tethered so it does not get blown away or dragged by the belt. The belt is to simulate ground effects, that are not present in a fixed floor wind tunnel. Without the (proposed) fan, it tests only for ground effect, but in a limited way. BMW have similar belt/fan combo, that is actually in use.

http://www.windshearinc.com/services/services_wind_tunnel_anatomy.htm#services

THAT ONE IS DONE.

 

[humber]

Indeed. It sounded like an innocent enough question - but the parallels are becoming increasingly obvious.

Don't forget to look under the bed.

 

[temporalillusion]

ETA: and we are still waiting for you to explain exactly how you can differentiate between the three aircraft carrier scenarios by jumping up and down.

Well he said you can measure the water and see that the ship has an engine so that's all the answer you'll probably get.

He showed many pages ago he doesn't understand how airplanes generate lift for all to see and didn't follow up with that either, or explain how his example of a sphere moving in relation to itself makes any sense, so the aircraft carrier can just go on the list of unanswered abandoned things to dance around.

 

[humber]

Well he said you can measure the water and see that the ship has an engine so that's all the answer you'll probably get.

He showed many pages ago he doesn't understand how airplanes generate lift for all to see and didn't follow up with that either, or explain how his example of a sphere moving in relation to itself makes any sense, so the aircraft carrier can just go on the list of unanswered abandoned things to dance around.

The rolling road example has made mugs of you all. Done seen a pictcha.
A few questions from profpangloss exposes Spork's barefoot physics.

 

[temporalillusion]

Ah yes, the "hey look over there" defense.

 

[humber]

Ah yes, the "hey look over there" defense.

The "don't check the reference" approach has busted you flat.
Only you think the ship has any relevance, so you may keep it as a blanky if you like.

 

[A.T.]

Then you tell me: in the frame of reference in which the air is at rest, where is the kinetic energy of the simple sail cart coming from?

Still no answer to this from the "new" guy? I'm so "surprised".

 

[Subduction Zone]

Still no answer to this from the "new" guy? I'm so "surprised".

Yes, we asked hm too many questions that Harold/Christoph/schroeder/yevgheni couldn't answer.

 

[ThinAirDesigns]

Profpanglos, you apparently agree that energy is frame dependent. Excellent.

In the frame of the wind before it encounters the blades of a garden variety wind turbine, what (besides the correct answer "ground") powers the wind turbing.

Thanks
Je

 

[tobermoryphil]

The "don't check the reference" approach has busted you flat.
Only you think the ship has any relevance, so you may keep it as a blanky if you like.

The ship (aircraft carrier) is totally relevant. It's deck is a mechanically propelled plane surface, and, if sailing in still air, exactly equivalent to the treadmill's plane surface.

But we do not expect you to get that, however much you jump up and down.

 

[profpangloss]

Gravity only exerts a force oriented toward the center of the earth, it doesn't act to "pull" things along with its rotation. That is, suppose that the core of the earth were rotating at an enormous speed relative to the surface. This would not tend to pull things on the surface in the direction of the core rotation, even though the core is providing significant gravitational pull. Forgive me if I'm stating the obvious, but it is not clear that you understand this..

Yes, yes that is true but it is also true that the gravitational mass of the object, under the acceleration of gravity is equal to a downward force that the object exerts on the surface of the planet, correct? That force is met by an equal force upwards, the force normal, that the planet exerts on the object. Where the object meets the surface there is friction. On the surface of the earth it is that friction which dominates over the inertial mass, to keep the object in place. If you want to move that object along the surface you must break the bond of static friction and then keep working against the kinetic friction whether rolling or sliding. The role of inertia is masked by that friction in normal non-laboratory settings. That is what I am talking about here, normal setting with a cart on a road, energy must be used to move against mgk where k is the coefficient of friction. Only if the object is on a frictionless surface can inertia play a significant role.

Energy is required to overcome the tendency to move with the treadmill as well. Accelerating something on the treadmill will cause the treadmill motor to expend more or less energy to maintain speed, depending on the direction of acceleration. Accelerating something on earth in the east-west direction will slightly slow down or speed up the rotation of the earth, depending on the direction of acceleration. Either way, for a small vehicle relative to the treadmill size and a small vehicle relative to the earth size, the treadmill and earth are effectively not accelerated (any change in the treadmill speed or the earth's rotational speed are too small to matter), and the vehicle behaves and performs the same in either case..

Ah, but we have seen that the treadmill can cause the cart to move up the belt in still air. Spork has already agreed the energy to do that is coming from the treadmill and not the wind. The treadmill apparently can do something the road cannot do; it can transfer energy to the cart that allows the cart to move against the direction the tread is moving. I have seen no evidence at all that a road can do this. If you can show me how a road can do this, I may start to believe the road is the same as a treadmill. But I seriously doubt you can do this.

Again, the treadmill was never used or needed to analyze the cart's performance, only to provide a very convenient and consistent testing platform.

Yes. I think it is a little too convenient! I don’t see that it has anything at all to do with a cart on a road.

There was one. If you know any physics professors, go ahead and ask them. I don't think you will be able to find any who disagree with the equivalence, other than on minor technical grounds (if the treadmill is too small and weak relative to vehicle size, there will be differences). The answer is in your own experience though. When you walk around on the deck of a ship that is moving at constant speed in calm water, or on an airplane that is cruising at constant speed and altitude, do you become disoriented and fall over? Do you have to alter your gait? No, you don't. You walk the same, and expend the same amount of energy, moving about on those moving platforms as you do moving around on the earth's surface.

I know a lot of qualified people and I have already asked. Contrary to what you say, I have found no qualified physicist who believes the treadmill is the same as a road. I am not talking about moving about on moving platforms as opposed to moving about on the surface of the planet. I am talking about getting energy from moving platforms as opposed to getting energy from the surface of the earth and using that energy to move against the motion of the earth. It is obvious to me the former is possible but not the latter.

 

[profpangloss]

You are a snake in the Garden of Eden, so they will assume that you are one of the Devil's disciples, Harold. That is, they are suggesting you are Harold Bricer. Rule: There can only be exactly 3 snakes. Me, Yevgheni and Harold: though many think the latter are the same poster.

Ah I see. Sounds too much like a cult to me but whatever floats their boat.