Collected, edited and extended by Donald Simanek.

1. Just rolling along.

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3. Figure 3 shows another friction (or geared) roller contacting the hub. A beam rests on the top of it. Same questions. As the beam rolls forward a distance of 3 on the green axle, the wheel rolls forward 13. The wheel moves 13/3 as fast as F. Now you see why we use a beam or geared rack to apply the force, for a rope or string would go slack if the cart moved faster than F. None of these give motion in a direction opposite to F.
4. Now, can you devise a mechanical cart that will travel opposite to the direction of the applied force, slower than the agent applying that force moves? Many mechanisms can be invented to go opposite to the direction of the applied force. Perhaps the simplest is a wheel and axle with the axle resting on two parallel rails. Now wrap a string around the wheel so it exits at the lower rim of the wheel. Pull the string and the wheel rolls in the opposiste direction that you are pulling. This one (4) moves the wheel slower than the agent applying the force F, and in the opposite direction, as required. 5. Now, can you devise a mechanical cart that will travel opposite to the direction of the applied force, faster than the agent applying that force moves? I don"t have a picture of this one yet. Still time to submit your own designs.

2. The Terrible Resistor Tetrahedron.

This electrical network contains five equal resistors and one resistor that differs markedly from the others. How can you identify the different resistor by using only
not

3. The classic resistor cube.

4. The classic resistor pyramid.

6. Walking the dog.

Answers to the other problems.