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Tony Ronco
(tr-browsing) - MLife
Re: A Question for You Physics Experts on 01/02/2013 00:03:47 MST Print View

Here is an attempt to address Art's question with a small attempt at brevity :-)

First Some Cerebral Background:
The human gait cycle has multiple parasitic losses.
Two of the primary losses are:
1.) vertical losses due to a person's center of mass moving a small amount up & down during the gait cycle and
2.) horizontal losses due to transient leg accelerations / decelerations to maintain ambulation at an average velocity.
(There are plenty of other losses such as the collision of the heel strike, etc., etc.,) but these two will suffice for now.

So, just considering these two factors; the faster the gait, the greater (frequency of) the acceleration/decelerations (vertical and horizontal) will be needed.
... That translates to greater force being needed ... and that translates to greater energy being needed (to complete the distance)

Now, to finally answer Art's question: The faster hike will require more energy.

(He already intuitively knew this, now he has a cerebral explanation too. *smile*)

How much more energy? Among other things, that would depend on Art's engine (= his state of physiological fitness) and his efficiency of technique (greater efficiency = greater reduction of parasitic loss)

Hopefully this helps.

Need more info?
Google: "walking gait cycle accelerations decelerations"
if more information is needed.

Edited by tr-browsing on 01/02/2013 00:30:15 MST.

Jeremy B.
(requiem) - F - M

Locale: Northern California
Re: Re: Re: run or walk on 01/02/2013 00:30:54 MST Print View

Uh, plain English?

Hah! Now I'm worried I missed something given the numbers I got. But in simpler terms, I think the work needed to get moving is greater with increased speed, and the stopping doesn't restore any lost calories. (i.e. no Prius-style regenerative braking.)

Franco Darioli
(Franco) - M

Locale: Melbourne
A Question for You Physics Experts on 01/02/2013 00:55:59 MST Print View

I just love all those formulae...
All I did to arrive to my conclusion was to think of how I go to town and back by foot.
It takes me 50 minutes or so to get there, then I usually walk about for a couple of hours and then I walk back.
I do all of that without having a drink, food or rest .
Sometime I have a coffee..
However if I sped myself up by 1/3rd I am pretty sure that at some point I would need to have a drink and eat something so that would indicate to me that I would have burnt more calories.
nevertheless as I stated many times my thinking is not scientific at all.

a b
(Ice-axe)
Re: Re: Re: Re: run or walk on 01/02/2013 00:56:34 MST Print View

There is no free lunch.

Walking faster than the mechanics of your legs can tolerate introduces kinetic losses.

What "faster" means is subjective.

Jardine had a section on this in his book from 1992.
Pretty much concluded that going faster was more efficient.
Typical engineer thinking.
As a plumber we are forever justifying the imaginary world of the engineer to the real world.

I think the more individual approach Nick Gatel has voiced recently is appropriate.

Either way, you always get less energy out of any system you put energy in to.

What lies between ->enegy in, and energy out<-, are the losses.
Engineer or plumber.. they are in-escapeable.

There is no free lunch.

By the way, this is also why solar panels and wind turbines will never amount to a mere small percentage of our energy production in this or any country.
How do you store energy when the sun does not shine or the wind does not blow?
How do you store energy of a hiker decending a trail?

You can spin up a turbine or flywheel but you always lose more energy than you have input to the system.(In the long term. Solar and wind turbines take 20 years to "re-pay" their investment in energy to create them. Long before that they fall well belew their stated efficiency standards)
So solar panels and wind turbines are actually a loss for society in general but a win for the individual user.

We can learn something from this.
Something that relates to the energy produced by a hiker climbing a hill.
This is not to say it is a lost cause.
Solar and wind and hikers are a great LOCAL source of energy.

They are not a great GLOBAL source of energy.

Go up that hill at a speed that suits YOU and physics be damned.

Edited by Ice-axe on 01/02/2013 01:03:16 MST.

Jeremy B.
(requiem) - F - M

Locale: Northern California
Re: Re: Re: Re: Re: run or walk on 01/02/2013 01:26:25 MST Print View

a b: Yep, I assume that the most efficient pace for anyone is that which takes the most advantage of the natural swing of leg and arm.

I can see solar eventually becoming more useful; particularly when paired with superconductor technology to store and distribute the power. (I think that's still quite far in the future.) There's a lovely chart of US energy flows up at https://flowcharts.llnl.gov/ that also shows how much is lost in transit.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: Re: Re: run or walk on 01/02/2013 08:39:43 MST Print View

"By the way, this is also why solar panels and wind turbines will never amount to a mere small percentage of our energy production in this or any country.
How do you store energy when the sun does not shine or the wind does not blow?"

That's the problem

If you have more long distance power lines you can transfer power from where you have excess to where it's needed. If you double the voltage, and increase tower height by 50%, you will reduce losses for a 1000 mile transit from 50% to 10% (something like that - too lazy to find accurate numbers)

If the power company had control of the bottom element of your water heater, they could turn it off when they don't have enough power.

Solar power units that melt some medium like sodium, could then store it for hours until power is needed, then use it to create steam to create electricity.

Big air conditioning users could freeze water during the night when there's excess power, and then use it to cool the building when there's a shortage of electricity.

If we eliminated all the subsidies that fossil fuels have got, from our "best government money can buy", then alternate energy sources would be more viable.

Nick Gatel
(ngatel) - MLife

Locale: Southern California
Re: Re: Re: Re: Re: Re: run or walk on 01/02/2013 09:01:48 MST Print View

"By the way, this is also why solar panels and wind turbines will never amount to a mere small percentage of our energy production in this or any country.
How do you store energy when the sun does not shine or the wind does not blow?"

That's the problem

-----------------------------

One other thing. When solar and wind farms are not producing energy, they need energy from the grid to stay active. They don't just shut down. Wind farms use something like 20% of their output when off line.

You cannot take conventional power plants off line permanently because you need their capacity when wind and solar are not producing.

The mammoth Ivanpah Solar System in California will use the sodium technology Jerry discussed. Only it covers 4,000 acres of land, which will no longer be able to absorb CO2 or support the life it once did. An ecological disaster -- there is no free lunch.

My rant can be found here: Green Greed

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: Re: Re: Re: Re: run or walk on 01/02/2013 09:26:38 MST Print View

Ha ha ha - good to have Nick back : ) I've read your rant. Like the Don Quixote analogy...

Since this thread is "question for you physics experts" and it's already degenerated to chaff even if not officially there...

According to http://en.wikipedia.org/wiki/Cost_of_electricity_by_source

Clear winner is - cost of natural gas is about $70 per MWh if you use a "combined cycle" - whatever that is - and I think since the cost of natural gas is dropping it's even better

Then hydro is $90 - but we've dammed all possible rivers so we can't increase this

Then there's a tie for about $100 between coal, geothermal, and wind turbines

Nuclear is $110

But then you have to factor in subsidies

We allow coal to produce huge amount of pollution which kills people - we should tax to pay for this. And getting the coal out of the ground destroys all that land in Appalacia and other areas.

The government did all the research to develop nuclear in the first place, and we exempt them from liability for leaks - if we ended that all nuclear plants would immediately close

What the government should do is figure out how to better use all that natural gas that we're discovering because of fracking. We could use it to power vehicles instead of gasoline from Saudia Arabia.

But we'll run out of this eventually, so we should develop alternatives in parallel so we will have solution to storage problem.

Plus, as we discover how bad global warming is going to be, even the natural gas which produces less CO2 than other fossil fuels, will become unviable.

Art ...
(asandh) - F
Re: Re: Re: Re: Re: Re: Re: Re: run or walk on 01/02/2013 09:30:21 MST Print View

I really enjoy learning about wind and solar energy, but since I doubt I'll be running with these technologies on my back ... maybe in a different thread.

I appreciate all the great input so far, thanks.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: Re: Re: Re: Re: Re: Re: run or walk on 01/02/2013 09:40:32 MST Print View

"I really enjoy learning about wind and solar energy, but since I doubt I'll be running with these technologies on my back ... maybe in a different thread."

Sorry Art - I couldn't help myself responding to someone else's misinformation : )

To answer your question, it's intuitively obvious that it takes more energy to go the same distance at a faster rate.

It's a physiology problem too difficult to solve using engineering/physics

If you look at advice for loosing weight, they say you loose more weight running faster. Like, they measure the amount of CO2 exhaled while running on a treadmill. I don't have a source, I just vaguely remember from somewhere - maybe PBS.

Amount of CO2 exhaled... that takes us back to global warming...

Tony Ronco
(tr-browsing) - MLife
Re: Re: Re: Re: Re: Re: Re: Re: Re: run or walk on 01/02/2013 10:10:29 MST Print View

"It's a physiology problem too difficult to solve using engineering/physics"

Engineering and Physics are two foundational cornerstones for physiology. The physical science of physiology can not exist independently without them.

-------------------

As previously stated: there is no free lunch.
The faster you go, the more prominent the parasitic loss of energy.

Edited by tr-browsing on 01/05/2013 06:24:36 MST.

M B
(livingontheroad) - M
power on 01/08/2013 15:53:34 MST Print View

Work=Force*Distance
Power = work/time
Force=mass*acceleration (= weight here basically)

One of the most difficult things to accept for some people , is that with no D, there is no work. I.e. you can struggle and sweat to hold up 100 lbs until you collapse. But if you dont move it, you havent done any work on it. The faster you move it thru the same distance, the higher you power output is, but the same work is being done.

If you have 100 lb wt on wheels, and roll it horizontally, did you do any work?
In a frictionless world, Nope. Even though you might move it, the only resistance to it moving horizontal is friction. In reality you know that may be a substantial amount depending on how good the wheels are and what the surface is. Same applies when your body is the "wheels", its called innefficiency.

The real base work you do would be lifting your body weight , the vertical distance you lifted it by going uphill. That doesnt change, its the same in both cases.

You need a higher power output to do so in a shorter time, thats why you are more tired.