Another model demonstrating the principle of the cart that moves down wind faster than the wind. Inspired by some ideas posted on the discussion at forums.randi.org, I made a simple cart that is pr...
Another model demonstrating the principle of the cart that moves down wind faster than the wind. Inspired by some ideas posted on the discussion at forums.randi.org, I made a simple cart that is propelled underneath a moving surface, faster than that surface. The large wheel, turning against the direction of movement of the ruler, is very similar to the propeller of the wind-powered cart, turning against the wind.
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You are all partially right, even coolaun. ALL the radius(circumference) ratios play a part in making this device move faster than the ruler. Some ratios work better some worse. Just think in terms of your transmission and tire size. Some ratios will not even work because sufficient force might not be transferred to move the device. See the videos "It works" then "8 to 40" and last "40 to 40". Perhaps you'll figure it out.
nadahere, mathematical analysis shows that the size of the blue wheel plays no part in the relation between speed of cart and speed of ruler. This is easily confirmed in an empirical test. If the radius of the ends of the cotton reels is b, the radius of the part of the cotton reels where the blue wheel touches them is a, Vr is the speed of the ruler and Vc that of the cart, then:
Vc = Vr(b/(b-a))
The cart goes faster when the two values are close.
I made a general statement regarding ratios of gears/wheels their velocities, power transfer and non/functionality. I should have clarified that if the center wheel was small the ruler might not be able to transfer enough force to make the device work. Ergo, even the center wheel contributes to making this device move faster than the ruler.
Yes, indeed: when b = a the cart doesn't work! Up to a certain point, the closer a is to b, the faster the cart goes in relation to the ruler (you can see this if you look carefully at panoik's videos). But this can't go on indefinitely: when a is very close to b, the ruler starts to slip. You can see what happens when b is exactly equal to a in avian6's video, "Experiments with a three-roller cart": when the ruler is moved, it just skids over the wheel.
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Vc = Vr(b/(b-a))
The cart goes faster when the two values are close.
:p