Talk:Lever/Archives/2015

"Leverage" listed at Requested moves

An editor has asked to change the use of Leverage, for the discussion, see talk:Leverage (disambiguation) -- 65.94.43.89 (talk) 21:15, 21 March 2015 (UTC)

Classes

I'm unsure, but it appears to me that the description of the 1st and 2nd class levers are switched around. The book im looking at (American School Physical Science Study Guide) has these levers listed as the opposite. Basically, the 1st class lever on wikipedia is listed as 2nd class in book, and 2nd class on wikipedia is listed as first class in the book. If anyone can clear this up that'd be great. Thanks!

My twelve-year-old daughter says that they are not mixed up in this article.

Is there a class like class 1 where the effort is closer to the fulcrum than the load or is that still concidered class 1? Tsinoyboi 11:15, 22 September 2006 (UTC)

• That's still class oneBeefpelican 02:47, 8 February 2007 (UTC)

Of course 1st and 2nd class levers can be switched around. It all depends on the use: for if you're using a canoe paddle as a 2nd class lever; the water is the fulcrum, the bottom hand is the output/canoe, and the top hand is the input. The output/bottom hand (canoe) travels in the same direction as the input/top hand. However; once the water begins to travel backwards, it ceases to be a fulcrum, and the bottom hand becomes the fulcrum. The top hand remains the input, for the lever is now used as a 1st class lever to move water (output) in the opposite direction. My favorite 2nd class lever is the oar of the row boat, which is usually incorrectly illustrated as a first class lever: showing the oarlock as the fulcrum, and the water as the resistance. Since the rowboat actually moves in the direction of the force, the oarlock is actually the load, and the water is the fulcrum (with the oar's blade remaining fixed in location). Kinipopo 10:11, 24 March 2007 (UTC)Kinipopo 09:54, 15 February 2007 (UTC)

So the '1st vs. 2nd' terminology is ambiguous and unhelpful ! --195.137.93.171 10:25, 15 September 2007 (UTC)

Canoe Comments:

The paddler is exerting force on the water. By Newton's 3rd law, that means that a propulsive force is exerted on the canoe.

But, from the point of view of the paddler, he's doing nothing other than exerting a force on the water.

Therefore the paddle (to the extent that we pretend that one of the paddler's hands is stationary with respect to the canoe) is being used as a lever of the class whose fulcrum is at one end (the "stationary" hand), so that motion is in the same direction at the effort (the other hand) and at the load (the water).

Levers of that class can, of course, have either the effort or the load closer to the fulcrum than the other (and that does not justify defining those 2 arrangements as two separate "classes"). Of course the paddle is the kind of lever for which, at the load, the motion is greater, and the force less, than at the effort.

Of course that's a big simplification, because, in real canoe-paddling, both hands are moving backwards.

[end of comment] 108.132.202.166 (talk) 22:01, 10 October 2015 (UTC)

If the paddle is left in as an example, I think the above should be made clearer - from the point of view of a paddler, it seems more intuitive that one of the two hands on the paddle is the fulcrum, so it appears that putting the paddle under 2nd class levers is an error. And is a springboard really a lever? It seems to me that the effort is the person bouncing on the end, and the load would therfore be the force pushing them back up - this does not obviously fit into the description of a lever. NorthernSpinney 29.2.08 —Preceding unsigned comment added by NorthernSpinney (talk • contribs) 12:26, 29 February 2008 (UTC)

The prose describing the 3rd class lever appears to work hard to justify it's usefulness. Most backhoes, cranes and bulldozers use hydraulic lifts within a third class lever. Thy hydraulic cylinder can give plenty of force so multiplying force is not necessary, while getting more distance is what the lever is useful for. I think it should be made clear in the description of the second class lever that it always multiplies force and in the description of third class lever that it always multiplies distance. The first class is first class because it can do both.

 —Preceding unsigned comment added by Shutoffyourtv (talk • contribs) 07:50, 6 January 2008 (UTC) 

More examples: Ice tongs = third class (paired) Paper cutter, guillotine style = second class I think you should get rid of the wrench example - too sketchy. 71.131.192.217 (talk) 09:04, 7 January 2008 (UTC)

Improved the 3rd exampre regarding the human arm. No reference necessary, all common sense and basic anatomic knowledge ALGHRV (talk) 23:23, 12 February 2010 (UTC)

I wish to suggest the following additions.

In the lede: In general, a lever is used for a selection of three things: to change the direction of the application of force where it is impractical to apply the force directly in the desired direction; to apply a greater force (this is the conventional definition of "leverage"); or to increase the speed at which the force is applied (increase the "velocity ratio"). The last two are mutually exclusive; see the cost/benefit below.

An example of the change of direction is to use a one's body weight on a crowbar to lift a heavy object off the ground. It is impractical to stand under the object and apply a force directly upwards; but it is highly practical to exert a downward force (the weight of one's body due to gravity) on one end of the lever, converting this into an upward force on the object at the other end of the lever.

The benefits of both leverage and velocity ratio increase both come at corresponding costs. Where the applied force is increased by the lever, the applied force has to be moved a corresponding greater distance. Where the velocity ratio is increased, the corresponding force is decreased by the same ratio.

Put more succintly, a lever creates one of the two cost X benefits:

• lower speed / shorter distance X increased force (leverage)
• decreased force X higher speed / longer distance (velocity ration increase)

In the "Classes" section: A first order lever can, in principle, increase either the leverage or velocity ration. A second order lever can only increase the force, and a third order lever can only increase the velocity ratio.

Also in the "Classes" section, a very worthwhile example for discussion is the boltcutter versus wirecutters/pliers. Wirecutters and pliers are a pair of first-order levers. A boltcutter is effectively a pair of pliers working on a wirecutter, thus the effective leverage is enormous (the leverage of the pliers X the leverage of the wirecutter); at a cost that the force has to be moved a much greater distance. I am happy to supply a photo of all three in open and closed positions, with notations on the photo to illustrate the point.

Another, more fundamental, problem with the "classes" classification:

The fact that some authors oppositely define class 1 and class 2, is something to be expected in a much-written-about subject, especially given the changing fashions over the decades.

But here's the real problem: The "class 1", with the fulcrum in the middle, and in which the movement at the load is in the opposite direction as the movement at the effort--isn't sub-classified according to whether the effort or the load is closer to the fulcrum.

But that's the only difference between class 2 and class 3--the two classes in which motion is in the same direction at effort and load, and the fulcrum is at one end. If that doesn't make a class-subdivision for the fulcrum in the middle, then it shouldn't make a class-subdivision when the fulcrum is at one end.

So I suggest that there are only two classes of levers: Fulcrum in the middle, with opposite-direction motion at effort and load. And fulcrum at one end, with same-direction motion at effort and load.

Simple.

With either of those 2 classes, the load might be closer to or farther from the fulcrum than the effort is--resulting in a mechanical advantage or a mechanical disadvantage.

But, when the fulcrum is at the end, the issue about whether the effort or the load is in the middle doesn't have class-relevance. All that's relevant about that is that when the load is closer to the fulcrum than the effort is, that's a mechanical advantage, in both classes of levers (fulcrum in middle, and fulcrum at end).

[end of comment] 108.132.202.166 (talk) 22:01, 10 October 2015 (UTC)

Finally, in the examples, the Trebuchet and "casting with a fishing rod" are excellent classical examples of the third-order lever. Old_Wombat (talk) 10:13, 7 October 2011 (UTC)

Added commment:

Actually, according to the article's classification, the trebuchet is a 1st class lever. Its fulcrum is in the middle, and motion is in the opposite direction at the effort and the load. The effort is closer to the fulcrum than the load is, and so the load moves farther, impelled by a force lower than the effort.

That disction regarding whether the effort or load is closer to the fulcrum doesn't result in a division into two separate classes. Therefore, neither should it do so when the fulcrum is at one end, and the motion is in the same direction at the effort and the load.

[end of comment] 108.132.202.166 (talk) 22:01, 10 October 2015 (UTC)

"Levers", as the idealised machines described here, are a single rigid strut with a single, fixed fulcrum. Canoe paddles and trebuchets are neither.

Canoe paddles (in kayaks) are a pair of joined third order levers (but otherwise quite simple). For Canadian canoes, they can be examined as either third or first order levers. There is no fixed fulcrum, both hands generally move together, but in opposite directions.

A trebuchet has two levers. The wooden beam is a simple first order lever. There's also a sling beyond this though, and this sling moves relative to the wooden lever as the beam accelerates, giving the change in "gear ratio" that makes the trebuchet so effective at giving a high projectile velocity. It's not trivially analysable as a simple lever. Andy Dingley (talk) 22:25, 10 October 2015 (UTC)