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# Simple Machines

Sun 6 Nov, 2011 11:26 am
What is the cost of having a simple machine with a large mechanical advantage?
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Type: Question • Score: 4 • Views: 3,671 • Replies: 29

1
Sun 6 Nov, 2011 11:30 am
@ilovethebeach13,
a good used motorcycle runs a coupla hundred bucks.
0 Replies

Ragman

1
Sun 6 Nov, 2011 11:31 am
@ilovethebeach13,
eleventy three dollars.

Seriously if you want an accurate answer you need to supply more info.
0 Replies

Fido

1
Sun 6 Nov, 2011 11:40 am
@ilovethebeach13,
ilovethebeach13 wrote:

What is the cost of having a simple machine with a large mechanical advantage?

Tightening a bolt with a wrench, or using a boat winch to do almost anything requiring power without speed would be good exambles... Our bodies are built for speed rather than power, and our joints work much as snow shovels, giving speed without mechanical advantage... I may be using the term machine incorrectly since it is the combination of a power with gearing that gives an advantage, our bodies with a tool, or an engine with a transmission and wheels...You may notice that the use of circular motion is foreign to people... Children must be quite advanced to understand the notion of peddles on bikes... Prehisotically, even grind stones were not used with a circular motion, but with a large pole were rocked against another grind stone... If a kid is advanced enough conceptually to be potty trained they supposedly can learn to peddle... Does this help???

The cost can be quite moderate... I have seen boat winches as low as three dollars at yard sales... One still must invest energy to make them work...
0 Replies

fresco

3
Sun 6 Nov, 2011 01:32 pm
@ilovethebeach13,
Monetary cost is meaningless here. You simply mean what is the "trade off" for a small effort to shift a large load, and that is that you need to move the effort a large distance in order to move the load a small distance.
The logic of the trade off comes from the equations:
Work = Force x Distance
Work In =Work Out (ignoring friction)
small effort x large distance =large load x small distance (ignoring friction)

Butrflynet

1
Sun 6 Nov, 2011 04:37 pm
@ilovethebeach13,
If it is too simple and has a large mechanical advantage, the chances of someone else coming along and duplicating it are high. That could be very costly to your profits.
roger

1
Sun 6 Nov, 2011 04:58 pm
In physics, a simple machine is a lever, gear, or inclined plane. You probably couldn't patent a wedge anyway, unless the design were truely unique.

1
Sun 6 Nov, 2011 10:40 pm
@ilovethebeach13,
ilovethebeach13 wrote:

What is the cost of having a simple machine with a large mechanical advantage?

Time, generally. And friction losses.

A pulley lets you lift heavier weights, but you have to pull more rope.
0 Replies

wayne

1
Mon 7 Nov, 2011 08:02 am
I would have to say, the cost relates directly to the energy spent acquiring materials and constructing the machine.
Riding a Bicycle to the store, as opposed to walking, saves time but requires roughly the same energy. The energy spent producing the Bicycle is the cost of the machine.

( edit ) Actually, the Bicycle adds some weight to the equation too, so there is an additional cost in this case.

1
Mon 7 Nov, 2011 09:14 am
@wayne,
Considering the relative efficiencies of walking vs. riding over a good road, the bicycle comes out way ahead.

The reduction in friction due to the wheel eliminates a lot of effort, so your example is not really valid.

I think the original post should read "trade-off" instead of "cost."
farmerman

1
Mon 7 Nov, 2011 09:16 am
@Butrflynet,
Tree fiddy
0 Replies

Fido

1
Mon 7 Nov, 2011 10:11 am
@fresco,
fresco wrote:

Monetary cost is meaningless here. You simply mean what is the "trade off" for a small effort to shift a large load, and that is that you need to move the effort a large distance in order to move the load a small distance.
The logic of the trade off comes from the equations:
Work = Force x Distance
Work In =Work Out (ignoring friction)
small effort x large distance =large load x small distance (ignoring friction)

Nothing much beats a worm gear, but hydralic pressure can be better...
Fido

1
Mon 7 Nov, 2011 10:13 am
@roger,
roger wrote:

In physics, a simple machine is a lever, gear, or inclined plane. You probably couldn't patent a wedge anyway, unless the design were truely unique.
In reality, a wheel, or gear as you have it is both a lever and an inclined plane... Just think of the center of the wheel as a fulcrum..
0 Replies

wayne

1
Tue 8 Nov, 2011 07:19 am
I'm no mathematician so I can't say just how great the friction reduction is, but even a good bicycle has added 17 lbs or so to the equation. Are you still including the man in your considerations? The bicycle reduces the contact area, adds friction for the chain, pedals, bearings, + 20 lbs or so, you've still got all the inefficiency of the power source.
I'm not sure exactly what the OP wishes to know here, all else being equal it requires x amount of energy to move something y distance.
The ideal machine doesn't include a power source, the cost of such machine would be the energy required to produce such machine. But I'm not sure if that's the question.

1
Tue 8 Nov, 2011 07:22 am
@wayne,
wayne wrote:
all else being equal

That's kinda my point....
wayne

1
Tue 8 Nov, 2011 07:37 am
I thought as much.

1
Tue 8 Nov, 2011 07:46 am
@wayne,
consider that work=force x distance

Get a concrete block, push it across the floor. Lots of force needed, which means lots of work.

Put the concrete block on a mover's dolly, push it across the floor. Very little force, which means lots less work than just sliding it across the floor.

Wheels eliminate a huge amount of friction, which reduces the necessary force, which reduces the amount of work.
fresco

1
Tue 8 Nov, 2011 08:04 am
@Fido,
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)
wayne

1
Tue 8 Nov, 2011 08:08 am
Sure it does, and a bicycle is far more efficient than the human body, my point, however, was that I wasn't eliminating the body from the equation. It's not quite the same as the cinder block example, you've still got all the friction of the power source. You might compare carrying the block to using the dolly, and don't eliminate the power source for the dolly in your considerations.
No matter though, we both understand you can't get free energy, a mechanical advantage translates to the speed ratio, nothing more, same energy.

1
Tue 8 Nov, 2011 08:31 am
@wayne,
I never claimed that you were eliminating the body.

I claimed that riding a bike is a lot more energy efficient than walking.

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