Down wind faster than the wind

[mender]

Davefoc, I'll try to address your concerns with a few excerpts from one of the other conversations that I've had on another forum. It'll be a little long but hopefully will explain what is happening. I leave out the propeller altogether to show that there is nothing magic about it.

Part 1: speed

A new illustration. A simple pulley system. One end of the string is attached to the ground. The string loops forward to a pulley that has a toy parachute attached to it. The string then comes back and attaches to a small wheeled cart. Another small wheeled cart with a flat sail is placed beside it.

Put both outside in a steady wind and let go of both carts. The sail cart takes off quickly and reaches a speed just under the windspeed. The parachute also takes off but more slowly because of the load of the wheeled cart and the gearing. If enough string is used, at some point the parachute also reaches a speed just under the wind speed.

How fast is the pulley cart going? Yes; twice as fast as the parachute. Faster than the wind that is powering it. Will it beat the other cart? Yes, if they go far enough.

Runs out of string - oops! Need to design a different gearing system between the air and the ground that won't run out of string. See the plans listed by spork referring to a prop cart.

 

[mender]

Part 2: force

A fishing reel with lots of line is attached through a scale to the ground. The other end of the fishing line is attached to a sail cart. The sail cart with a fishing line attached to it is released in a 10 mph wind. It reaches 9 mph, losing 1 mph because of rolling resistance.

You apply the brake on the fishing reel to slow the cart down to 8 mph and read the amount of pull (force) on the scale. Let's say it reads 100 grams. Based on these numbers, how much rolling resistance does the cart present to the wind when it is traveling at 9 mph in a 10 mph wind?

Now you slow the cart to 6 mph. How much force does the scale show?

Give the math a try before reading the following answers.

First question: since the law of conservation of momentum applies to the air being slowed, we can easily figure out what the rolling resistance of the cart is at 9 mph. When the cart is slowed to 8 mph, the air impinging on the sail (wind) is also slowed to 8 mph from 10 mph. This is twice the amount of speed difference that just the sail cart itself slowed the air. Since the amount of energy in the wind is the square of the speed difference, the amount of drag that is shown on the scale is four times the rolling resistance of the cart, minus one because the rolling resistance of the cart is still present. So the amount of drag that the cart experiences at 9 mph is 33.3 grams (100 divided by (4-1)). The total force on the sail by the 10 mph wind when the cart is moving at 9 mph is 33.33 grams. The total force on the sail by the 10 mph wind when the cart is moving at 8 mph is 133.33 grams (2 squared = 4 times as much). Simple physics and simple math.

Second question: by slowing the air down to 6 mph from 8 mph, the amount of force shown on the scale increases. Again, since the amount of energy harnessed by the sail is the square of the speed difference, the total amount of force on the sail is four times as high as the total force from the first question. That amount is 533.33 grams. The cart still has the original drag of 33.33 grams, which doesn't reach the scale. The scale reads 500 grams. Again, simple math but the right math.


So how many carts can the wind pull at 6 mph from the same size sail? Easy; 533.33 grams divided by 33.33 is 16 carts.

Instead of having the pulley attached to a parachute from my previous example, attach the pulley to the sail cart. Attach one end to the ground and the other end to a cart without a sail. Release them in the 10 mph wind.

You've already tested the amount of force available and the rolling resistance of the cart. Even given some horrendous losses due to friction in the pulley and doubling the rolling resistance of the cart and adding some aerodynamic drag to compensate for the second cart moving faster than the air around it, the amount of force provided by the wind exceeds the force needed to pull the second cart ( no sail) to twice the speed of the 6 mph sail cart by a substantial amount. That would be 12 mph, which is faster than the wind. The second cart, pulled by the force of the wind being slowed to 6 mph from 10 mph by the first cart, provides all the force needed to achieve that 12 mph.

Note that we don't need to know the weight of the cart or the size of the sail to answer the questions.

Did this help you understand the magnitude of the forces involved?

 

[mender]

Just for humber, in part 1 what happens if the string is attached to a weight instead of being anchored to the ground and the weight starts to slide along the ground?

 

[Subduction Zone]

Here is another humberism:
You are being lured into a phony sort of relatively with this absolute/can't tell line.
Yes, but I need only know. JB says that I can't tell the wind of his porch on a belt from the real. If the wind on my real porch changes, I see no acceleration, but on JB's they are directly related. I can also use a gyroscope. They have the characteristic of being orientated "to a fixed point in space". The earth is also a gyroscope, so its axis of rotation is in alignment with an unfettered gyroscope. This allows absolute position on the earth to be determined. Common on ships.
Now I can say that I am moving relative to the ground, and in which direction, and that the wind is artificial, so Mythbusted.

Then he pulls the example of a gyrocompass and tries to use that as an example. Notice humber you said a fixed point in space, not a fixed direction. There is a big difference between the two. Here is a simple example that even humber might understand. Grab your gyrocompass, starting due south of your house you can see that your compass points towards your house (the chosen point in space). Now walk so that you are due west of your house, your gyrocompass still points due north. It is still pointing in the same direction but not at the same point.

 

[humber]

Here is another humberism:
You are being lured into a phony sort of relatively with this absolute/can't tell line.
Yes, but I need only know. JB says that I can't tell the wind of his porch on a belt from the real. If the wind on my real porch changes, I see no acceleration, but on JB's they are directly related. I can also use a gyroscope. They have the characteristic of being orientated "to a fixed point in space". The earth is also a gyroscope, so its axis of rotation is in alignment with an unfettered gyroscope. This allows absolute position on the earth to be determined. Common on ships.
Now I can say that I am moving relative to the ground, and in which direction, and that the wind is artificial, so Mythbusted.

Then he pulls the example of a gyrocompass and tries to use that as an example. Notice humber you said a fixed point in space, not a fixed direction.

Google it. See if you cannot find that expression. I even tell you that it is commonly used notional expression you still blindly lumber on.

There is a big difference between the two. Here is a simple example that even humber might understand. Grab your gyrocompass, starting due south of your house you can see that your compass points towards your house (the chosen point in space). Now walk so that you are due west of your house, your gyrocompass still points due north. It is still pointing in the same direction but not at the same point.

So? Are you suggesting that I cannot use a magnetic compass to tell the I am moving in a particular direction? The axis is relative to the earth. What more information do you need? Must is be engraved on a tablet?

However you choose to relabel it, I can still tell I am moving.
Large ships use this gyro-compasses because magnetic devices are effected by the ships steel structure. Look it up. If that information does not suggest to you how you may use it on a moving belt, then the problem is yours.

 

[humber]

Just for humber, in part 1 what happens if the string is attached to a weight instead of being anchored to the ground and the weight starts to slide along the ground?

Your argument is limited to velocity. Guess what? Some things can move relative to others. That's startling.

 

[ThinAirDesigns]

Here is another humberism:
JB says that I can't tell the wind of his porch on a belt from the real. If the wind on my real porch changes, I see no acceleration, but on JB's they are directly related.

And the real key to that humberism is that in his answer he isn't sticking to the parameters of the problem -- *steady state*. He's waiting for a *change* to make a determination. Sadly for him as the test is defined, there is no change coming.

As demonstrated by tsigs answer "I'll wait for the power to the teadmill to fail", in steady state humber also can't make any determination without some outside reference.

He loves to use his "Mythbusted" statement without acknowledging that he has yet to address the actual test -- let alone solve/bust it.

Humberverse is a very interesting place.

JB

 

[humber]

Part 2: force

Is that relevant? I wonder how that does not simply confirm that the belt does indeed drive the cart to a minimum, even though that is its claimed to be at maximum velocity. In fact, it must be true for the cart to stay on the belt.

 

[fredriks]

Is that relevant? I wonder how that does not simply confirm that the belt does indeed drive the cart to a minimum, even though that is its claimed to be at maximum velocity. In fact, it must be true for the cart to stay on the belt.

Cant you perform a test of this important result in humberian physics and film it so we all see that humberian physics are correct?

It would be simple to do with a treadmill. Just put a couple of different objects on a working treadmill and see what is happening. Humberian physics seems to say that everything would stay still compared to the room, i.e. moving relative to the belt.

Some possibly objects that you can test.

A orange.
A brik.
A computer.
A standing man.
Any cart.
A boing 747.

 

[ThinAirDesigns]

Point to the video and timestamp.

Asked and answered. Spork posted the link long ago and you've been arguing about it endlessly since.

JB

 

[humber]

Asked and answered. Spork posted the link long ago and you've been arguing about it endlessly since.

JB

Yes, you agree, its the same video. Is this the third time you've tried this?
Of course, I have told you that the test itself is not as important as the fact that you have fitted the experiment. Your posts confirm that you have done that. So please append that information to the next attempt.

 

[humber]

And the real key to that humberism is that in his answer he isn't sticking to the parameters of the problem -- *steady state*. He's waiting for a *change* to make a determination. Sadly for him as the test is defined, there is no change coming.

As demonstrated by tsigs answer "I'll wait for the power to the teadmill to fail", in steady state humber also can't make any determination without some outside reference.

He loves to use his "Mythbusted" statement without acknowledging that he has yet to address the actual test -- let alone solve/bust it.

Humberverse is a very interesting place.

JB

You seem to have forgotten that you told me that I could not tell io was on your porch. I have refuted that. I can think of more ways, but as you know one is enough.
(1) Accleromter. As soon as I step on the belt I know. If you sart the belt with me on it, I know.
(2) Gyrocompass(s) will tell me my motion relative to the ground.
(3) Magnetic compass, same.

But I don't have to do that. I can simply show that my porch is not moving, so yours must be. You can't tell me that yours is moving. unless you agree that mine isn't.
Like it or not, you all tacitly agree that the ground is a reference.

 

[spacediver]

Risible. You are using "feels like" as an instrument. Folk physics. (51%, remember). Wow! tragic error.
It's the fact that the forces are not only equal but opposite, but maximised. Forces are maximised not minimised at terminal velocity. I put a gauge in the skates, so that you wouldn't fall into your own trap. Oh, boy, Spork has it easy!

Humber, this isn't freefall terminal velocity, where the air resistance builds up over time to match the force of gravity, in which case you'd be more or less correct.

CORed was discussing a much different type of scenario, where the primary motive force is a tailwind, in which case, the force on the parachute or umbrella actually is at a minimum at maximum velocity.

Consider the following scenario:

You're standing still on ice, with ice skates. You are topless.

On the middle of your back is a ripe pimple, ready to explode.

A strong wind develops and pushes you forward (so the wind is pushing against the pimple).

You accelerate, due to this force, until your forward velocity matches that of the wind. At that point, you cease to accelerate, and maintain a steady velocity.

Question: when is the pimple more likely to pop?

You contend that since forces are maximized at maximum velocity, it would be more likely to pop at this maximum velocity.

We contend that it would be more likely to pop the moment the wind develops, since the unbalanced force of the wind is at a maximum at that moment in time.


Now, if you had a pimple on your chest, and there was air resistance to factor in, then yes the chest pimple would be more likely to pop at maximum velocity.

BUT WE WERE TALKING ABOUT THE BACK PIMPLE, NOT THE CHEST PIMPLE.

 

[spork]

So? Are you suggesting that I cannot use a magnetic compass to tell the I am moving in a particular direction?

You can only tell you're moving relative to something. A magnetic compass won't tell you if you have absolute velocity because there is no such thing.

The axis is relative to the earth.

And there we have it.

What more information do you need? Must is be engraved on a tablet?

I think we have all the info we need. You are apparently completely ignorant of the notion of inertial frames as well as the notion that velocity is ALWAYS relative.

However you choose to relabel it, I can still tell I am moving.

Absolutely wrong. You never fail to dissappoint.

 

[ThinAirDesigns]

I have told you that the test itself is not as important as the fact that you have fitted the experiment.

If the test was "fitted", it was only to your specifications -- it's your test done faithfully to your specific requirements with an outcome different from what you predicted.

JB

 

[ThinAirDesigns]

You seem to have forgotten that you told me that I could not tell io was on your porch.

And you seem to have forgotten the "steady state" requirement.

I can think of more ways, but as you know one is enough.

Before you can think of "more", you must first think of one. You have not yet done that.

(1) Accleromter. As soon as I step on the belt I know. If you sart the belt with me on it, I know.

Violates the steady state requirement

(2) Gyrocompass(s) will tell me my motion relative to the ground.

Not in a horizontal steady state it won't.

(3) Magnetic compass, same.

Violates the "without outside reference" requirement.

But I don't have to do that. I can simply show that my porch is not moving, so yours must be. You can't tell me that yours is moving. unless you agree that mine isn't.

Now you're trying to peek and compare your porch to mine -- violating once again the "without outside reference" requirement.

Like it or not, you all tacitly agree that the ground is a reference.

There is no such agreement and so far you have failed miserably to produce any test which addresses the problem.

JB

 

[Subduction Zone]

I think I may have figure humber and his humberverse out. He must be a Flat Earther. That is show by his total rejection of Newton's and Galileo's concept of inertial frames of reference. The kicker is that now he seems to think that "North" is a point in space, and not a direction. The only place that I know of where North can be called a point is the Flat Earth's center of the world map. He is an interesting troll though, without him this thread would have died a peaceful death long ago since spork and JB have put forth their side very well. Well I am sure that we will here from him once again, as soon as he gets his dealer to drop off some more meth.

 

[humber]

You can only tell you're moving relative to something. A magnetic compass won't tell you if you have absolute velocity because there is no such thing.

And there we have it.

I think we have all the info we need. You are apparently completely ignorant of the notion of inertial frames as well as the notion that velocity is ALWAYS relative.

Check it out. Wikki it. Gyroscopes are an inertial reference. That's why they are used to steer Hubble. Your argument is false.

None of that matters. You said I could not tell your wind from the real wind. You cannot change the wind unless you accelerate the belt. You can Wikki "absolute acceleration". But I need only relative acceleration for the wind. The gyroscope will tell my absolute velocity wrt the ground. The wind is over the ground, you tell me so.
I can use GPS. I can tell because the designers were not so stupid as to launch a system that could not do that. The reference clock is on the ground.
If you say not, then that's another case where you think everyone is wrong.

You say that my test fails because there is no absolute velocity. Why do you keep doing that? All velocities are relative, of course, that's understood. There can be no other type of ground/porch velocity arrangement, other than relative.
Your claim that the treadmill is indistinguishable from the real world equivalent is false. That undermines your claims of windspeed.

Absolutely wrong. You never fail to dissappoint.

Now, being wrong, is that absolute?

 

[mender]

Is that relevant? I wonder how that does not simply confirm that the belt does indeed drive the cart to a minimum, even though that is its claimed to be at maximum velocity. In fact, it must be true for the cart to stay on the belt.

Yes, humber, it is relevant. As you noted, part 1 was about velocity (speed), explaining that something can go faster than the wind that is powering it if there is enough force to overcome the drag. Part 2 shows that a substantial amount of force is available, more than enough to achieve DDWFTTW travel in the example given.

These two concepts are the ones that most people have trouble with.

The cart on the treadmill is at maximum velocity when (1) the treadmill is level and running at 2.7 mph. It is also at maximum velocity when (2) the treadmill is inclined 4.4 degrees and running at 10 mph. In both cases, the speed of the cart and the speed of the air is the same, modeling what would happen if the cart was tested outdoors with the same conditions, i.e., (1) level road and 2.7 mph tailwind or (2) 4.4 degree hill with a 10 mph tailwind.

Clearly, if the cart was on a level treadmill running at 10 mph, the treadmill would have to be quite long for the cart to reach equilibrium. That would be, as a guess, about 14-15 mph relative to the belt and 4-5 mph relative to the air around it.

 

[humber]

I think I may have figure humber and his humberverse out. He must be a Flat Earther. That is show by his total rejection of Newton's and Galileo's concept of inertial frames of reference. The kicker is that now he seems to think that "North" is a point in space, and not a direction. The only place that I know of where North can be called a point is the Flat Earth's center of the world map. He is an interesting troll though, without him this thread would have died a peaceful death long ago since spork and JB have put forth their side very well. Well I am sure that we will here from him once again, as soon as he gets his dealer to drop off some more meth.

See what you've done there? You've avoided mentioning that a gyro compass will give me my velocity wrt the ground. Not to mention the accelerometer.