Explain Simple Machines to me

Factual Questions
1

Wikipedia lists the simplest machine types as:
*Lever
*Wheel and axle
*Pulley
*Inclined plane
*Wedge
*Screw

Now when I learned about simple machines, around the time of the Boer Wars, I was taught that there are three, not six: the wheel, the lever, and the inclined plane.

Aren’t the wedge and the screw just applications of the inclined plane? And the pulley of the wheel?

I looked them up because I sometimes try to figure out which simple machines something mechanical is made up of. This time it was a door hinge. Wheel, right? Lock: wheel and inclined plane.

Then I got stuck on zippers, which made me wonder if something could be mechanical and not be a machine. I mean a hook and eye to keep a door shut doesn’t seem to fit any of the basic types either.

Can anyone add to my understanding?

2

They are all based on the same principle as a lever and there is no official definition of how many or what are simple machines. Hooks and zippers aren’t machines, they’re fastening devices. The wiki definition of a machine is sufficient here:

" A machine (or mechanical device ) is a mechanical structure that uses power to apply forces and control movement to perform an intended action."

3

In all of these cases the power is from an outside force; applied power whose inertia is altered by the machine. Such force is applied to a zipper. Does the fact that each tooth of a zipper is essentially an inclined plane, wedged against another plane of a complementary inclination, make it “technically” a machine.?

4

The slider you pull on a zipper is a machine for connecting a chain of fasteners. The fasteners aren’t really machines though.

5

I’ve always thought (perhaps incorrectly) that a “simple machine” was a device that produced a mechanical advantage, thereby providing for a greater force to be exerted and tasks to be performed that would not otherwise be possible. By this definition the basic simple machines are the lever and the pulley. Gears are just a special case of a pulley system (and so is a screw, like the design of my car jack that allows me to easily lift a corner of the car off the ground) and in some sense all of them are just variants of the lever, trading off span of motion for force. If one holds to that definition, wheels, inclined planes, and wedges don’t qualify as machines.

6

Now when I learned about simple machines, around the time of the Boer Wars, I was taught that there are three, not six: the wheel, the lever, and the inclined plane.

Aren’t the wedge and the screw just applications of the inclined plane? And the pulley of the wheel?

I’m 71, so I learned about simple machines and wrote it down with a steam-driven pencil. Our teacher brought up this idea of the screw being an inclined plane wrapped around an axis. However, he said, to use a screw as a fastener, you’ll use a lever in the form of a screwdriver or wrench. If used as part of a more complex device, such as a grain auger, you’re converting rotary motion to linear motion, usually gaining a mechanical advantage.

The wedge is an inclined plane, but it’s usually used with a hammer, which is a lever.

I got tangled up the last time I tried to explain pulleys, bootstraps, and mechanical advantage. I’ll let somebody else 'splain that one.

7

So which type of machine is a zipper slider? I dont see where it aters the inertia of a force

8

It is an inclined plane. You may think that the inclined plane is on the zipper tooth, but the pull and the tooth are inclined relative to each other and you apply the force to the pull which transfers it to the zipper tooth to force it into place. Once wedged in position the zipper tooth does nothing, just like a nail driven into wood.

You can define it how you like though.

9

How is a pulley more fundamental than a wheel? Isn’t the former an application if the latter? And yes I was taught the same thing about about a screw being a modified inclined plane.

And how is a hammer a lever? Wouldn’t that make a rock a lever? or a boot?

10

Can you see a difference between a rock and a hammer? If you were to describe a hammer how many parts would you say it has? How many parts would you say a rock has?

11

Got it. The hand is the fulcrum.

12

. . . or would the fulcrum be the elbow, or the wrist, since the hand’s position in relation to tje hammer doesn’t change? In which case, is the hammer still any more a lever than the stone or boot, whose “fulcrum” is also the human anatomy?

13

The handle of the hammer is a lever. Rocks don’t have a lever. To use a rock like a hammer you have to use your arm as a lever or a ram. Either way, those are parts of your body, not part of the machine. In the case of a hammer the simple machine is the lever.

I don’t know of a simple definition for simple machines, nor do I think there is a need for one. The concept is just a way to introduce basic mechanical devices that are the components of other mechanical devices.

14

It seems to me that with a hammer, as with a rock, the fulcrum and lever at the human arm.

But I’m beginning to think that when you get right down to it, it’s as arbitrary and subjective as speciation.

15

Now you understand simple machines.

16

I wouldn’t go quite that far. Maybe more like “as arbitrary and subjective as” the levels of taxonomic classification (not so much what is a species or how many different species are there, but how many levels of taxonomy are there between species on one end and domain on the other).

17

I’m disappointed that Wikipedia still lists the “six simple machines”: Modern elementary textbooks have (thankfully) finally moved on from that list.

The old-fashioned list of six really does only include three, but not he way you’re breaking it down: A wheel (in the sense that it’s a machine) is just a kind of lever, but a pulley really is a distinct one, independent of the wheel.

The way you make a machine out of a wheel is by putting multiple wheels on the same axle, of different radii. But that just means that you’ve got a fulcrum at the axle, and different lengths of arm from that fulcrum. The only thing that makes it different from a lever is that you’re continually replenishing it: As one arm moves out of position, another arm moves in.

A pulley, meanwhile, could be made without wheels. Take low-friction materials, like nylon rope and a block of Teflon with grooves cut in it, and you could make a block and tackle without anything in it that could be described as a wheel. And it would still have the same mechanical advantage as a wheel-based pulley. It’d be impractical, because it’d have more friction, but it’d still work.

And there are many, many other simple machines. A hammerhead is another one. Yes, a hammer usually combines a hammerhead with a handle (which is a lever), but the lever isn’t the only part of the hammer providing mechanical advantage. To prove this: First try to drive a nail into a piece of wood with just your fist, and then pick up a decent-sized rock, and use that to drive the nail into the wood. You’ve got the same lever in both cases, your arm. But the rock is a primitive hammerhead, and that’s what makes the difference.

A sample list of simple machines I can think of off the top of my head (all of which are distinct, and any one of which can be made without using any of the others, hence “simple”):
*A lever
*An inclined plane
*A block and tackle
*An oblique line
*A hydraulic ram
*A generator-motor pair
*A hammerhead
*A spring

I don’t claim that this is a complete list; others can probably think of more. But it amply illustrates that the standard list of six is incomplete.

18

I don’t think a rock is a simple machine. It is no different from your hand in function, it is just harder.

A spring should be considered a simple machine, so should magnets and electromagnets separately. I think the best definition should be that simple machines are the basic components more complex machines are made from.

Also, wheels and pulleys are the same thing, but they come in two forms, free-wheeling on an axle, and attached to the axle. But any machine that consists of multiple simple machines like a block and tackle is not a simple machine.

19

The simple machines make it possible to do more work with less effort.

A lever allows you to lift much heavier objects than you could lift by hand.

An inclined plane allows you to move a load upward (or down) more easily than if lifting it.

A wheel, obviously, eliminates (or greatly reduces) friction with horizontal motion.

A pulley may be an application of a wheel - but compound pulley / block and tackle, by sequencing multiple pulley wheels, allows you to raise much heavier loads than you would be able to simply lift. by hand.

Screw, yes, is an inclined plane around a central core; but it also can translate rotary motion into linear motion (Archimedes’ screw lifts water, for example; augers do the same).

A wedge also might be a versoin of an inclined plane. - but agian, in this case it also translates linera motion into a perpendicular splitting motion when a wedge is hammered into a chunk of wood or rock. etc.

A hammer is simply the application of the value of momentum. You can hammer a nail in with a rock, if it is heavy enough and has a flat(-ish) side. A pile driver is a hammer that uses linear rather than rotational force…

When I learned these things way back when, i don’t recall the pulley or wedge being distinct simple machines.

These are “simple” because most other exploitations of power are based on these simple devices.

Springs simply store and release energy. electric or steam or combustion motors are sources of power; the “simple” machines make it possible to use that power to do work.

20

I remember reading an article about the rolamite in the 1960s, which described it as the first simple machine invented in modern times. (Sadly, Wikipedia still describes it that way.) As far as I can tell, the rolamite hasn’t found many uses since its invention; certainly all the other traditional “simple machines” are used many orders of magnitude more frequently. I’m not sure it’s really classifiable as a machine at all; it seems to be more a type of bearing.