PH physics boffins please help me
Discussion
Its more for my own curiosity than anything else but I just dont know which sums to do to work it out.
roughly how much energy would it take to shift my mass around a run I did recently?
will have to ignore things like frontal area and drag as I have no idea on the figures.
use weight as 95kg
distance as 16.25km the route also involves 500metres of hill climbing but the start and finish is in the same place so would that be evened out by the downhills?
time taken lets say 95 mins.
Secondly how much energy would be spent if the weight was only 70kg?
Thirdly how fast would the course be completed in theory if I were to use the same amount of energy as the original question but only weighed 70kg.
lastly how much energy would it take to make a 95kg person complete the course in 72 mins? and how much energy for a 63kg person to do same.
Thanks for any help
roughly how much energy would it take to shift my mass around a run I did recently?
will have to ignore things like frontal area and drag as I have no idea on the figures.
use weight as 95kg
distance as 16.25km the route also involves 500metres of hill climbing but the start and finish is in the same place so would that be evened out by the downhills?
time taken lets say 95 mins.
Secondly how much energy would be spent if the weight was only 70kg?
Thirdly how fast would the course be completed in theory if I were to use the same amount of energy as the original question but only weighed 70kg.
lastly how much energy would it take to make a 95kg person complete the course in 72 mins? and how much energy for a 63kg person to do same.
Thanks for any help
RB Will said:
..
will have to ignore things like frontal area and drag as I have no idea on the figures.
..
I'm afraid you can't do that. Unless your exercise is climbing a rope or flight of stairs most of the work done (energy used by your muscles) is down to air resistance and internal work within your body by the muscles.will have to ignore things like frontal area and drag as I have no idea on the figures.
..
(Some of) your mass is lifted up a bit at every pace but then lowered again.
You're gaining two kinds of energy: kinetic and potential.
When you gain 500m in altitude, your potential energy gain is m g h = mass * gravitation pull * height
= 95kg * 9.81m/s^2 * 500m = 466kJ
Of course, you then lose the same amount of energy on the way back down the hill!
Meanwhile, by accelerating to your running speed of (say) about 15kmh or 4m/s, you gain kinetic energy of 0.5 m v^2
= 0.5 * 95kg * 4^2 = 760J
These are very small numbers indeed, as it's all about friction with the air, against the ground, and within your own body. To look at it another way, it would take me 90 minutes to do your run (you may well be fitter than me!), and I'd suspect I'd be working at about 250W on average, or about a third of a horsepower. 250W * 5400second = 1350kJ. Rather depressingly, that's 322 Calories, or a bit more than a Mars bar...
When you gain 500m in altitude, your potential energy gain is m g h = mass * gravitation pull * height
= 95kg * 9.81m/s^2 * 500m = 466kJ
Of course, you then lose the same amount of energy on the way back down the hill!
Meanwhile, by accelerating to your running speed of (say) about 15kmh or 4m/s, you gain kinetic energy of 0.5 m v^2
= 0.5 * 95kg * 4^2 = 760J
These are very small numbers indeed, as it's all about friction with the air, against the ground, and within your own body. To look at it another way, it would take me 90 minutes to do your run (you may well be fitter than me!), and I'd suspect I'd be working at about 250W on average, or about a third of a horsepower. 250W * 5400second = 1350kJ. Rather depressingly, that's 322 Calories, or a bit more than a Mars bar...
I remember reading up on calorie calculators some years ago and deciding (after forgetting the reasoning behind it entirely) to simply half whatever calories whichever machine thinks I've burned and go with that. Not that I cared much in the first place.
But there's some interesting ideas come from Michael Phelps claims that he was eating 10,000 calories a day. How thermodynamics can play a large role.
The issue with exercise is that BRO SCIENCE! is everywhere. The general gist is to eat naturally occurring foods and do loads of stuff; the rational can vary BLUEBERRIES MELT YOUR STOMACH FAT THROUGH HORMONES!! to simply BURN MORE THAN YOU EAT!!! It's usually all guess work and mostly b
ks, but encourages - often by happy accident - a healthier lifestyle.
I appreciate this is a science forum, not exercise. Apologies if this is off-topic.
Edit; I think running is suppose to burn circa 130 cal per mile regardless of pace. It's an oft repeated stat so much be fairly accurate. But, as above, who knows what else will come into play.... wind resistance. Air temp. Flailing arms...
But there's some interesting ideas come from Michael Phelps claims that he was eating 10,000 calories a day. How thermodynamics can play a large role.
The issue with exercise is that BRO SCIENCE! is everywhere. The general gist is to eat naturally occurring foods and do loads of stuff; the rational can vary BLUEBERRIES MELT YOUR STOMACH FAT THROUGH HORMONES!! to simply BURN MORE THAN YOU EAT!!! It's usually all guess work and mostly b
ks, but encourages - often by happy accident - a healthier lifestyle.I appreciate this is a science forum, not exercise. Apologies if this is off-topic.
Edit; I think running is suppose to burn circa 130 cal per mile regardless of pace. It's an oft repeated stat so much be fairly accurate. But, as above, who knows what else will come into play.... wind resistance. Air temp. Flailing arms...
menguin said:
BoredNerd said:
I...It's an oft repeated stat so much be fairly accurate.
Not sure about that! As with the "five a day" recommendation it could well be a figure pulled out of thin air or dodgy calculations and been repeated ad infinitum.See also; Bees can't fly!!!
From a physics point of view (my background), running is dynamically a lot more complicated than lifting weights, the latter being simply potential energy gained and the calculations surrounding levers etc. However, even if you could conquer the physics of running, one would also need a biological perspective, because muscles (and to some extent joints) are not 100% efficient. Doing simple physics calculations on any exercise would be like calculating the fuel burnt by a car's engine by simply using kinetic energy, aero drag and mechanical drag - you would need to account for the efficiency of the engine as well.
RB Will said:
how about if we super simplify and forget about running and just say power/energy to move the weights in the times over the distance, even if the actual figures are way off then maybe at least the percentage differences can be used with a roughly known calorie count to extrapolate
The trouble is that the things you're suggesting eliminating are the core of the problem. With no resistance, friction or drag, it would take energy to accelerate the mass to running speed in the first few seconds, but then you need no energy at all to keep it moving. The whole effort of running is the air resistance, the motive method (bipedalism!), muscle efficiency, bounding up and down, etc; if you remove that then you'd have nothing left.RB Will said:
how about if we super simplify and forget about running and just say power/energy to move the weights in the times over the distance, even if the actual figures are way off then maybe at least the percentage differences can be used with a roughly known calorie count to extrapolate
Every time you take a step you are accelerating your foot from rest by lifting it. The same step also has you lifting and accelerating the rest of your body. How high/far you lift your foot depends on the gradient and your running style, the length of your leg.If you divided your running time by number of steps taken and counted each step as an individual acceleration of your mass in two directions you might be able to arrive at a figure, but I'm still not sure it would be any good in guessing calorie count. It would completely ignore the energy costs in your respiration, for one thing.
May offer some practical insights if not theoretical ones.
http://www.runningtools.com/energyusage.htm
An estimated time would kick things off.
ETA In fact there's a real time, as a run was completed recently.
The same uniform velocity (speed) could then be taken to give times for other distances not too far from the original, and used with different masses in the online calculator. This is an approximation of course as with a hill the pace will change.
Starting with 16.25 km and 95 mins gives 10.3 km/h which is about 6.4 mph
The nearest option in the online calculator is 5mph. Using this with the stated body mass gives 5.06 MJ but the calculation scales with speed so for 6.4 mph we get 6.5 MJ or 6500 kJ which can easily be converted into kcal.
For a body mass of 70kg using the same distance and time values, the online calculator suggests 4.26 MJ or 4260 kJ and 4300 is more in keeping with the accuracy of the approach.
This is with all other things being equal, which they won't be given the associated fitness changes that accompany the typical means of achieving body mass loss which result in the ability to sustain a faster average speed and achieve a shorter time, but it's an indication of the order of things unless there's a blooper beyond the approximations in the above run(!)-through.
The rule of thumb that running the same distance in a shorter time results in about the same energy expenditure appears to be confirmed by substituting appropriate values in the online calculator, with the greater rate of energy use (power) needed to sustain the higher speed cancelled out by the shorter time as far as the overall energy total is concerned. The calculator uses pace not distance after all.
http://www.runningtools.com/energyusage.htm
An estimated time would kick things off.
ETA In fact there's a real time, as a run was completed recently.
The same uniform velocity (speed) could then be taken to give times for other distances not too far from the original, and used with different masses in the online calculator. This is an approximation of course as with a hill the pace will change.
Starting with 16.25 km and 95 mins gives 10.3 km/h which is about 6.4 mph
The nearest option in the online calculator is 5mph. Using this with the stated body mass gives 5.06 MJ but the calculation scales with speed so for 6.4 mph we get 6.5 MJ or 6500 kJ which can easily be converted into kcal.
For a body mass of 70kg using the same distance and time values, the online calculator suggests 4.26 MJ or 4260 kJ and 4300 is more in keeping with the accuracy of the approach.
This is with all other things being equal, which they won't be given the associated fitness changes that accompany the typical means of achieving body mass loss which result in the ability to sustain a faster average speed and achieve a shorter time, but it's an indication of the order of things unless there's a blooper beyond the approximations in the above run(!)-through.
The rule of thumb that running the same distance in a shorter time results in about the same energy expenditure appears to be confirmed by substituting appropriate values in the online calculator, with the greater rate of energy use (power) needed to sustain the higher speed cancelled out by the shorter time as far as the overall energy total is concerned. The calculator uses pace not distance after all.
Edited by turbobloke on Wednesday 27th January 09:08
anonymous said:
[redacted]
No need to get all high n mighty about it, I have read every post here and anyway how do I butt into my own bloody thread!The quoted question had not been answered by yourself. You merely told me that simplifying it would not give me the answer I was after at the time. You didnt give figures for the theoretical situation you described.
There must be an answer for [Energy used to move an object (lets say a cylinder 1.8m tall and 40cm diameter) of x mass over x distance in x time, through air. Forget about ground and muscle friction etc]
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