How Mechanisms Work: What Happens When This Turns?

Questions

1. 1
   Not answered. A car's differential drives both rear wheels from one input shaft. What actually lets the outer wheel spin faster than the inner wheel when the car turns a corner?
2. 2
   Not answered. One rear wheel of a car sits on dry pavement; the other sits on ice. With a normal open differential, what happens when the driver presses the accelerator?
3. 3
   Not answered. In a standard lockstitch sewing machine, the needle carries a thread down through the fabric on every stitch. Where does that needle thread actually lock together with the bobbin thread?
4. 4
   Not answered. A Geneva drive takes a continuously spinning input wheel and uses it to move a second, driven wheel. What does that driven wheel actually do?
5. 5
   Not answered. A worm (a screw-shaped shaft) drives a toothed worm wheel. Why can you usually turn the worm to lift a heavy load, but you cannot turn the worm wheel backward to lower that load by pushing on it?
6. 6
   Not answered. A single universal (Cardan) joint connects two shafts that meet at an angle. The input shaft spins at a perfectly constant speed. Which of these are true of the output shaft's speed?
7. 7
   Not answered. A mechanical clock stores energy in a wound spring or a falling weight. What does the escapement actually do with that stored energy?
8. 8
   Not answered. A pin tumbler lock has several spring-loaded pin stacks pressing down into the plug. What has to happen across all of those pin stacks at once before the correct key lets the plug rotate?
9. 9
   Not answered. A bicycle freewheel lets you stop pedaling while the bike keeps rolling, but pedaling still drives the rear wheel forward. What inside the freewheel makes both of those things true?
10. 10
    Not answered. In a typical piston engine, the piston moves in a straight line while the crankshaft turns in a circle. How does the piston's speed actually change over the course of one stroke?
11. 11
    Not answered. A rotating cam pushes a follower up and down as the cam spins at a constant speed. What actually determines the exact up-and-down motion the follower traces out?
12. 12
    Not answered. A rack and pinion converts a pinion gear's rotation into the rack's straight-line motion. If the pinion is made bigger (more teeth, larger radius) while its rotation speed stays the same, what happens to the rack?
13. 13
    Not answered. A Scotch yoke converts a crank's rotation into straight-line motion using a pin that slides inside a slotted yoke. How does the yoke's back-and-forth motion compare to an ordinary crank-and-connecting-rod mechanism?
14. 14
    Not answered. A four-bar linkage has four rigid links joined by four pivots. If the same four links stay the same length but a different one is fixed to the frame, what happens to the motion the linkage produces?
15. 15
    Not answered. A planetary gear set has a sun gear, several planet gears riding on a carrier, and a ring gear surrounding them. Which of these are true about driving it?
16. 16
    Not answered. A compound gear train uses several gears of different sizes meshed in sequence to connect a fast motor to a slow, high-torque output shaft. Which of these are true?
17. 17
    Not answered. A bicycle rear derailleur moves the chain sideways between sprockets of different sizes. What actually forces the chain to climb from a smaller sprocket onto a larger one?
18. 18
    Not answered. A pulley-and-belt continuously variable transmission (CVT) changes its overall gear ratio smoothly instead of shifting between fixed steps. Which of these are true about how it does that?
19. 19
    Not answered. A block and tackle uses multiple pulleys and one continuous rope to lift a load. Which of these are true about how it multiplies force?
20. 20
    Not answered. A screw thread is often described as 'an inclined plane wrapped around a cylinder.' What does that description actually explain about turning a screw?
21. 21
    Not answered. A zipper's slider has no motor and grips no individual tooth by hand. As it is pulled along the zipper, what actually splits or re-meshes the two rows of teeth?
22. 22
    Not answered. A retractable click pen extends its tip on one press of the button and retracts it on the next, alternating every time, using only a spring and one button. What keeps track of whether the next press should extend or retract the tip?
23. 23
    Not answered. Pull several inches of steel tape out of a retractable tape measure and hold it out horizontally, unsupported. Why does the blade stay straight and rigid instead of flopping down under its own weight?