Since I had some success with my answer to the Car Talk fuel tank puzzler, I figured I would go the next step. There was another puzzler that I didn't like the answer for. Here is that puzzler.
Basically, the goal was to figure out a way to lower some slate without holding on to the sides at the end (because it fit just perfectly). The parameters of the solution said that a worker went to the kitchen and came back to make it work. Car Talk said the answer was to place the slate on ice cubes. When the ice melted, the slate would be lowered into place.
Here is my solution (that doesn't involve getting the sub floor wet):
So, how does this work? What lifts up the slate? The answer: air (well, maybe I should say the atmosphere). Here is a diagram of the slate with the cup and butter as viewed from the side.
This diagram is only showing the forces on the slate (not the forces on the cup). Note that I represented the force from the air as several forces - this is to try to emphasize that it is pushing all over the slate both on the top and the bottom.
The main difference between the force from the air on top and the bottom is the cup with the butter on it. The butter makes an air-tight seal so that air doesn't get under there. This small area under the butter could possibly not have any air pushing down on the slate. The net result is more air on the bottom pushing up than down so that the slate does not fall.
How big could this force from the air push up on the cup? Well, suppose the cup with butter has a diameter of 5 cm. This would have an area of about 2 x 10-3 m2. The pressure due to the atmosphere is about 105 N/m2. This would give a maximum net force of:
That is the perfect case, but that is still a huge amount to lift. In the case of the real piece of slate, you could easily use several cups (or even plates) for better control.
In the end, all you have to do is wipe off the buttery mess. Seems like this would be easier than water on your sub floor.
