wayne
 
  1  
Reply Tue 8 Nov, 2011 09:06 am
@DrewDad,
I know, and it is, I probably wasn't clear in the first place.
I'm considering this from the aspect of the ideal, in which case the output equals the input. I realize I wasn't clear about that.
I think the cost of the machine is whatever energy was required to produce it.
Within the ideal, you'll never recoup that expenditure, will you ?
DrewDad
 
  1  
Reply Tue 8 Nov, 2011 09:40 am
@wayne,
Universally, no, considering the second law of thermodynamics.

Locally, yes, or there wouldn't be any point in building machines to begin with.
Fido
 
  1  
Reply Tue 8 Nov, 2011 09:50 am
@fresco,
fresco wrote:

Worm gears and hydraulics tend to stray from what is taught under the heading "simple machines" in a basic physics curriculum . The topic headings tend to consist of : lever, screwdeiver, inclined plane, wheel barrow, scissors, nut-cracker. Secondary topics include gears, pulleys, car jacks. Then as a topic concerning transmission of pressure (=force/area) and the non-compressibility of liquids, hydraulic transmission might be mentioned with the trade off force and area (as opposed to force and distance)
Try to remember that every wheel, even geared wheels are like a moving lever and fulcrum, and something like a wheel barrow is a combination of two sorts of levers and fulcrums....
fresco
 
  1  
Reply Tue 8 Nov, 2011 10:12 am
@Fido,
No...the topic of "simple machines" is pedagogically separated from the topic of "turning moments", the reason being that the teacher (who used to be me) does not want the student to get confused between the concept of work (force x distance moved in direction of force) and moment (force x distance from fulcrum). The fact that the two measures of distance are geometrically proportional in the lever tends to be an unnessary side issue for students at that level.
Fido
 
  1  
Reply Tue 8 Nov, 2011 11:26 am
@fresco,
fresco wrote:

No...the topic of "simple machines" is pedagogically separated from the topic of "turning moments", the reason being that the teacher (who used to be me) does not want the student to get confused between the concept of work (force x distance moved in direction of force) and moment (force x distance from fulcrum). The fact that the two measures of distance are geometrically proportional in the lever tends to be an unnessary side issue for students at that level.
above, you linked a third degree lever with wheels as in wheel barrow, but if a wheel is presented as a constant lever, which it is, then you can easily tell why it has been so useful to humanity... Moment is certainly an element of it, but only an element... In fact, with other wheels, bearings to be exact, and lubrication, the moment reactions can be reduced to a point inconsiderable... In structural engineering, the force is met with resistencc... In the engineering of a wheel, the lateral forces, or the force of gravity, friction, or inertia might be more highly considerable than moment...In a building, moment forces must be resisted because buildings do not fall down, but twist down... Wheels are desgned to have little resistence to twisting on their axis...
fresco
 
  1  
Reply Tue 8 Nov, 2011 11:44 am
@Fido,
Quote:
you linked a third degree lever with wheels as in wheel barrow,

The wheels are irrelevant with respect to the wheel barrow being classified as "a machine". What matters for the categorization is the ratio of the lifting distances, and the ratio load to effort, not the fact that the mass eventually moves horizontally, which is an aspect of momentum and friction. (In that respect, I have manually pulled a 2 ton canal boat a considerable distance with little difficulty. No lifting involved of course !) .
roger
 
  1  
Reply Tue 8 Nov, 2011 03:42 pm
@fresco,
I think I would have to buy a worm gear as a special case of inclined planes.

By the way, if you want to see a really fast gear reduction and associated mechanical advantage, you should look at the potential of a worm and pinion arrangement.
0 Replies
 
wayne
 
  1  
Reply Tue 8 Nov, 2011 07:59 pm
@DrewDad,
Quote:
Locally, yes, or there wouldn't be any point in building machines to begin with.


Apparently there is, considering the paragon of inefficiency called the Automobile.
0 Replies
 
Fido
 
  1  
Reply Thu 10 Nov, 2011 11:16 am
@fresco,
fresco wrote:

Quote:
you linked a third degree lever with wheels as in wheel barrow,

The wheels are irrelevant with respect to the wheel barrow being classified as "a machine". What matters for the categorization is the ratio of the lifting distances, and the ratio load to effort, not the fact that the mass eventually moves horizontally, which is an aspect of momentum and friction. (In that respect, I have manually pulled a 2 ton canal boat a considerable distance with little difficulty. No lifting involved of course !) .
Up river or down... You may have been dealing with an inclined plane as well, and one with little friction, well lubricated...
0 Replies
 
EssayWriter
 
  0  
Reply Thu 22 Jan, 2015 08:43 am
@ilovethebeach13,
It is depend on machine functionality and quality.
Cost is always depend on quality of product .
0 Replies
 
 

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