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Physics Question - ma = mg
CatalinaWOW:
--- Quote from: bostonman on July 04, 2021, 02:59:50 pm ---
--- Quote ---Think of your body as a very inefficient car. It burns something like 1000-1500 calories a day sitting in a chair doing nothing. The work perform lifting a weight or walking a treadmill is almost negligible.
--- End quote ---
Ignoring for a moment that apparently Newtonian work is different than biological, I'm uncertain I agree with this statement. If someone has a desk job, and the best they can burn is 1500 calories, ninety-minutes on the treadmill burning 300 plus calories is 20% or more additional burnt calories. That could mean the difference of burning off your lunch, or not.
As for thinking I could use lifting an object to calculate calories burned, guess I need to research this.
--- End quote ---
I was flippant when I said almost negligible. If 90 minutes on a treadmill had no impact there would be no market for gyms. But the dominant use of the fuel you dump into your body is keeping the fires burning, powering your brain (the single largest consumer of energy in most humans) and doing other basic functions. Running, jumping and lifting and doing the kind of work described in physics makes relatively minor variations in the fuel consumption. Even for top athletes running ultra marathons or world strongest man champions the work output is far smaller than the housekeeping consumption.
In principal you can relate lifting weights to calories but the relationship will be very imprecise. Your body speeds up the background consumption during and after exercise so calories will be burned that aren't directed toward the lifting of the weight. Similarly you lift and drop parts of your body while lifting your weight set, complicating the calculation. That is why you will find the kind of empirical numbers you are referring to on your treadmill. Scientists have basically put people into a calorimeter while performing various types of exercise and work and measured the output. Your mileage will vary. Different individuals will get different results so while one person may burn 300 calories on that treadmill others might burn 200 to 600 (made up numbers, I know there is a range, but haven't studied it). I am quite sure that the marketing people for gyms and exercise equipment bias their quotes to the higher results.
bostonman:
It's unfortunate calories isn't more precise.
Some of these questions do revolve around the gym. For years I wondered how many say bench press reps would equal X minutes on a treadmill.
TimFox:
In physics, these terms are precise, but due to historical usage, the popular language confuses them.
Precisely: a calorie is the amount of heat that increases the temperature of 1 gram of water by 1 K.
A kilocalorie is the heat that increases the temperature of 1 kg of water by 1 K.
A BTU is the heat that increases the temperature of 1 lb av of water by 1 Fo, which brings us back to the definition of the pound: mass or weight.
bostonman:
--- Quote ---A kilocalorie is the heat that increases the temperature of 1 kg of water by 1 K.
--- End quote ---
Is this the reason when I first mentioned "calorie" burning at the gym, someone said it's really a kilocarlorie?
In other words, people who say they burned "calories" at the gym are really using it incorrectly?
TimFox:
That was me.
Of course, if you burn calories you certainly burn kilocalories, but a different rate.
The SI uses only Joules for mechanical, electrical, and thermal energy. 1 kcal = 4184 J.
At the gym, if you lift 1 kg up by 1 m, than is 9.8 J of mechanical work and potential energy. Therefore, lifting a 50 kg dumbbell by 1 m is 490 J, or only 0.117 kcal.
Once you leave the quiet rational space of the SI, you venture into a dense thicket of other units at your own risk.
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