Simple Machines: three or six?

He has to make

machines. The lever,

lever, the wheel

inclined plane."

maybe, when you add

is just an

wrapped around a

appears that

original three

inclined plane, and the

other of those, in that

So where is the fulcrum point on a wheel and axle? A lever needs to have a fulcrum point to work...... phil

At the axle.

Thanks for the reference Spehro. My, time really does fly I guess. This is the article I remembered:

Popular Science (March 1966) "Frictionless Machines from Rollers & Bands" by Harry Walton

Surprisingly few applications are noted. I guess the features may have been supplanted by newer ideas. Or it may only have been overlooked?

dennis in nca

What a neat mechanism! I'm most impressed with all the variations they thought of. But I've never seen one in a product (and I've taken apart a lot of stuff). There must be some drawback(s) that limits their use (if any) to apps where low friction is critical.

Bob

The centerline of the axle, of course.

cylinder

lever

In that case it is only the radius of the wheel. A lever _must_ have three points of interest to be labeled a lever. The point of application, the fulcrum point and the resultant point. A lever can be attached to a wheel by connecting it at 'two' points, not just one. One point is the fulcrum and the other is the resultant point. Lever, wheel, separate items. I'm surprised no one has come up with a simple assembly that uses all _three_ machines in a demo! Nothing but blabber about the alphabet. phil

You have a better argument with "W" than "Y." Actually, "Y" is pretty common: cry, by, sky, why, wry, spy, gym, crypt, hymn, lynx, myth, glyph, slyly, tryst, nymph, Gypsy, pygmy, flyby, syzygy, etc.

I grew up on a street named Twyckenham....

Try substituting "i" for the "y" in each of those. Those are all "i" sounds, some long, some short.

Again, there is no unique vowel sound signified by "y." It's just a substitute for various pronunciations of "i."

An old street, no doubt. d8-)

-- Ed Huntress

rigger

of

One

Lever,

I just thought of a way to explain the lever/wheel thing. Say you have this big spike sticking out of the floor and you decide that it must be pulled. You find this nice chunk of round bar with a small v-notch on one end that fits the spike. Perfect fit. You grab the other end and try to move the spike but nothing happens, you swing the bar around all over the place keeping the v-notch on the spike. All you have done is develop the surface of a sphere. And the spike is still there glaring at you. Then you find a short chunk of 2x4 and put it close to the spike and bear down on it. Voila! The spike comes out! What changed? You added a fulcrum point changing the rod from a radius of a sphere (wheel) to a lever. Now how can you say a wheel and a lever are the same thing? No way... Same thing if you put an arm onto the axle. It'll just swing on it and do nothing to the wheel until you tack weld it in one place. Now the tack weld is one point, the side of the hole in the arm making contact with the axle makes the second point and your hand on the outboard end can now turn the wheel at will. Make sense? Lever: 3 points.... phil ;>))

Nothing says that two (or even all three) of the points can not be in the same place.

The special case of a lever of zero moment -- physically indistinguishable from a wheel of zero radius, or a wedge of zero length. In effect, a point.

These are good thought problems for conceptual thinking; exercises in practical geometry. But they're not the way to start teaching kids how machines work, which was the original problem.

This question of whether to teach three basic machines (or two -- gawd) versus six is a good thought problem itself, if the thought it about how to teach and how one learns. Calling a screw a "wedge wrapped around a cylinder" is good for geometry class or for students who have gotten past the ideas of how basic machines work. But it's a special case, too, in which any meaningful motion is rotary, whereas we think of a wedge as something linear. It can confuse rather than illuminate.

I learned three basic machines in physics class, too, and it was interesting. But six sounds better as an introduction. Keep reducing it with the special reductive cases and you wind up with pulleys that do nothing and everything else disappearing -- an interesting thought in itself, but an abstract one, of no use in understanding actual machines, unless you live in another dimension.

I like the six machines for introducing basic mechanics. Then show them how these can be reduced to a smaller number. Then you can reduce them all to a point, at which event everything crawls up its own asshole and becomes a Klein Bottle in the fifth dimension. d8-)

-- Ed Huntress

Good answer!! That SHOULD be the final word in this discussion, but I'm sure it won't be.

Bob

They forgot the Turing Machine.

And the State Machine, Democratic Machine, Mr. Machine, Espresso Machine, Wayback Machine, _Time Machine_ ...

--Winston Machine

On Wed, 26 Nov 2008 16:52:31 -0800, the infamous Winston scrawled the following:

Don't forget Mann and Machine, poo. I loved the teeny perts on that robot. Yancy Butler is a fox!

Good here

Better here:

But the whole idea of teaching about "simple machines" is to demonstrate that every other machine is made of these elemental devices. To follow your logic, we may as well teach that a bicycle is a simple machine and, sometime in the future, clue the kids in to the fact that a bike is really a "special case" of a combination of wheels, levers, etc.

Sorry, I don't see how teaching a kid that there's a difference between a "wedge" and an "inclined plane" helps to build their understanding of mechanics, reason or intellect. Same with "wheel" vs. "pulley".

As for the Kid Down The Street, while discussing how he might incorporate screws into his design, I showed him some examples in my shop. There was the leadscrew on my lathe, the various fasteners, and the flutes on an auger bit. He had a hard time with the auger, saying something like "I don't know if my teacher will accept that as a screw, since it doesn't really screw anything together." Sheesh.

I then took that auger bit and stuck it in a plastic tube and dropped a ball bearing in. Turning the auger, I raised the ball to the top of the tube. We then talked about the Archimedes Screw pump

Of course, this kid's idea of a "simple machine" is anything that predates an Xbox 360...

"Phil

rigger

the

lever

point of

can not be in the

indistinguishable

effect, a point.

exercises in

teaching kids how

two -- gawd)

thought it about how to

around a

have gotten past

case, too, in which

wedge as something

it was

Keep reducing it with

that do nothing and

itself, but an

unless you live in

Then show them how

reduce them all to a

and becomes a

But the whole idea of teaching about "simple machines" is to demonstrate that every other machine is made of these elemental devices. To follow your logic, we may as well teach that a bicycle is a simple machine and, sometime in the future, clue the kids in to the fact that a bike is really a "special case" of a combination of wheels, levers, etc.

Sorry, I don't see how teaching a kid that there's a difference between a "wedge" and an "inclined plane" helps to build their understanding of mechanics, reason or intellect. Same with "wheel" vs. "pulley".

As for the Kid Down The Street, while discussing how he might incorporate screws into his design, I showed him some examples in my shop. There was the leadscrew on my lathe, the various fasteners, and the flutes on an auger bit. He had a hard time with the auger, saying something like "I don't know if my teacher will accept that as a screw, since it doesn't really screw anything together." Sheesh.

I then took that auger bit and stuck it in a plastic tube and dropped a ball bearing in. Turning the auger, I raised the ball to the top of the tube. We then talked about the Archimedes Screw pump

Of course, this kid's idea of a "simple machine" is anything that predates an Xbox 360...

...............................

Another example of lever, wheel, inclined plane would be the good old wheelbarrow, eih? Hey you, get these bricks up to those masons there, eih? Ya, just go up that there ramp, real easy.......;>) phil

Yeah, I get the point, and that's how I was taught. I'm just thinking aloud about how you really can best teach mechanics from the start. I've never tried it so I can't be sure, but some people are better at abstract thinking than others, and abstracting mechanisms to the three basic machine elements from the start may not be the best way to do it. I'd have to see the results of teaching to be sure.

But take your bicycle as an example. Specifically, take the chain. There's a system that transmits force, and power, with...what, a couple of hundred moving parts, if you count the rollers on the pins? And not one of them is a wheel, a wedge, or a lever. Maybe you could make a case for the rollers rotating on the pins, but I'd rather not, because, at best, it's confusing.

It's an interesting question from a teacher's point of view, and I'm not convinced that the old methods are best.

"Sorry, I don't see how teaching a kid that there's a difference "between a "wedge" and an "inclined plane" helps to build their "understanding of mechanics, reason or intellect. Same with "wheel" vs. ""pulley".

A wedge wrapped around a cylinder cannot produce a straight screw. It's always cone-shaped. But an inclined plane can produce a straight screw.

Good for Archimedes screw pumps, leadscrews, and such. But that isn't most screws. So, again, it's a question of where you start for the sake of clarity. Once the basic mechanisms are recognized, I agree, I'd show how they reduce to a few basic elements.

I do wonder how kids cope with the obscure and almost magical quality of the electronic devices with which they interact every day. When I was a kid I believed that I could understand everything around me if I just studied it enough. Now, much of it seems to have passed some threshold of comprehension. They must look at things in a fundamentally different way.

-- Ed Huntress