Direct Downwind Faster Than the Wind #2 (DDWFTTW)

JB shamelessly stole MarkC's design and had to try it for himself. This really does make a slick little cart that nicely shows that it is possible to make a simple wind powered vehicle that goes downwind faster than the wind.

Category:

Science & Technology

Tags:

• DWFTTW
• DDWFTTW

[spork33]

@ Teekles

You've got to learn about Galilean relativity. It says that moving the surface under the air is no different than moving the air over the surface (i.e. wind). When you ride your bike directly downwind at 10 mph in a 10 mph wind, what do you feel? Nothing. No wind.

When our treadmill belt is going 10 mph, and the cart stands still, it also feels no wind. That's because it's going downwind at wind speed - as measured by an observer on the treadmill belt.

[XMark3]

how about a treadmill video angled to view to the left of it so we can confirm that someone isn't turning a fan on when the cart is placed on the treadmill?

[spork33]

Look at "Downwind Faster than the Wind #7"

[thacount1]

Maybe you should stop showing the treadmill "experiment" as if it is equivalent. On the treadmill, energy is coming from the treadmill and being transferred to the propeller which acts in the still air of the room pushing the cart forward. This is a completely different situation than having the cart (with no other power source than the wind) moving at the same speed as the wind. At that critical point the relative speed between the propeller and the wind is 0 mph.

[spork33]

You need to look into the principle of equivalence of inertial reference frames. Galileo, Newton, and Einstein tell us that a cart on a stationary road in a 10 mph tailwind is IDENTICAL to a cart on a road that's moving 10mph under "no" wind.

[triestelondon]

I don't have access to the equipment so I'd be curious to see the results of placing the cart on a stationary treadmill, then starting the treadmill...

[spork33]

Yes, as subductionzone points out, the minimum wind speed for this cart to go faster than the wind is 2.7 mph. Given a long enough treadmill it would backup until the treadmill was going 2.7 mph, and would then start advancing forward.

[Teekles]

@Teekles well actually its not upwind-but its not downwind. The treadmill is moving backwards at lets say 10mph. Well, since the car is not moving on the treadmill, the wind speed is effectively 0. The wheels spinning at 10mph forwards is NOT the same as a 10 mile per hour wind from behind.

[Teekles]

..one problem, YOUR GOING UPWIND

[goatpunch]

Really this is as simple and as counter-intuitive (at first) as the yo-yo along a table & cotton reel examples.

Basically the cart is being _pushed_ by the wind, and uses the rotation of the wheels to turn a propeller which pushes against the wind even more and allows it to move a little faster than the wind which is pushing it.

Most people seem to assume that they see a windmill (turbine) which powers the wheels.

[subductionzone]

It would probably fall off of the end of the treadmill. It takes a little while for the propeller to speed up enough to provide thrust. Another problem from following their videos and blogging is that if the "wind" is below 2.7 mph this particular design will not work, on the treadmill that means it will just go back until the speed of the treadmill is a least 2.7mph.