After struggling to teach pulleys and inclined planes and levers for decades, I am finally beginning to understand them. Working with levers and wheels-and-axles and gears I became convinced that every machine designed to multiply the input force could become a machine that multiplies speed just by switching the input and the output.
A steering wheel is a force multiplier - it takes a small force from your hands at the wheel and outputs a large force at the tiny shaft. A drive axle attached to a wheel is a speed multiplier - it takes a large force from the transmission and outputs a small force at a high speed for the outside edge of the tire. A steering wheel is the reverse of the drive axle.
 |
Axle turns Wheel
Speed Displacement Multiplier
Mechanical Advantage < 1.0
|
 |
Wheel turns Axle
Force Multiplier
Mechanical Advange > 1.0
|
That much I could figure out, but the pulleys and inclined planes were a tougher job. I looked them up many times and inclined planes and wedges and pulleys were always shown with a mechanical advantage greater than 1.0 - force multipliers. Then I switched the input and output forces and suddenly pulleys could be speed multipliers too.
Wedges were tougher. I finally figured out that if I stamped on a door wedge it could shoot out at a really high speed if there weren't much friction. Flip the input and output forces and the force multiplier becomes a speed multiplier.
Inclined planes are always treated as force multipliers, but the Winter Olympics solved my conundrum. I watched those Sochi snowboarders launch to ridiculous heights and land safely on the slopes and the LED blinked on. Rather than landing on level ground and breaking bones, they were using the incline as a force divider - a displacement multiplier - mechanical advantage less than 1.0.
Now I'm one step closer to understanding "simple" machines. Thanks, Vlad
No comments:
Post a Comment