### Author Topic: Physics Question - ma = mg  (Read 9372 times)

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#### JohnnyMalaria

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##### Re: Physics Question - ma = mg
« Reply #150 on: July 13, 2021, 01:16:03 pm »
Quote
herefore, lifting a 50 kg dumbbell by 1 m is 490 J, or only 0.117 kcal.

Just tell me if I'm going over the deep end or just reverting to "calories" being incorrectly used. So if I eat a Snicker's Bar at whatever.... 100 calories, does this theoretically mean I have to lift that dumbbell 855 times (100 divided by 0.117) to burn off the snack?

Or are calories on nutrition labels using the wrong units?

Seems about right. An innocent Snickers (or half a pint of chocolate milk, some fruit etc) can ruin the benefits of your short trip to the gym.

This shows a table of typical calorie expenditures for various types of exercise. Damn those high energy density peanuts!

https://www.brianmac.co.uk/energyexp.htm

#### bostonman

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##### Re: Physics Question - ma = mg
« Reply #151 on: July 19, 2021, 02:22:49 am »
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Bostonman is on his way to understanding the complexity.  Most aren't interested or don't have the capacity.

I appreciate the compliment. I find that many don't care to dive into understanding many items we use in life or general concepts.

With me, sometimes I try digging too deep for no reason.

Often times I have an appreciation for when the math matches real life situations. Obviously anomalies get thrown in the loop, however, being an "engineer", tossing in approximations can help avoid a lengthily and unnecessary list of calculations.

As for kilo-calories, a slight reason exists why I somewhat switched to this area. The first is because were discussing Work. The other reason is due to going to the gym. It would be nice to have an idea that if I pickup something and place it down, that it will equal (on a theoretical level) X minutes on the treadmill.

I'd like to think that if I lift weights for an hour and someone brags they walked an hour on the treadmill, that I can scientifically state that taking a Neanderthal approach burned an equal (or more) amount of calories.

#### RJHayward

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##### Re: Physics Question - ma = mg
« Reply #152 on: July 26, 2021, 02:51:46 am »
Yes, BostonMan, your direct work has potential (no pun) health benefits. BUT, don't ignore the warm-up stuff; doing light stretches, and movements. Postures such as standing on one leg, alternating, that's great as (we) age.
Heck, sincerely, look at some YOGA or TaiChi practice, ,(maybe can skip some of the strength work).
The simple stretches eliminate some resistance in body movement.
In older days, folks didn't look to burn calories, except maybe their horses'.

#### bostonman

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##### Re: Physics Question - ma = mg
« Reply #153 on: July 26, 2021, 02:56:20 am »
As for this thread, and my questions deviating towards burning calories, this would be totally different.

I'm still focused on the math/physics of being able to argue differences when someone brags they did an hour on the treadmill and feel they burned more calories than someone lifting weights.

#### JohnnyMalaria

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##### Re: Physics Question - ma = mg
« Reply #154 on: July 26, 2021, 02:31:35 pm »
As for this thread, and my questions deviating towards burning calories, this would be totally different.

I'm still focused on the math/physics of being able to argue differences when someone brags they did an hour on the treadmill and feel they burned more calories than someone lifting weights.

Simple answer for such folk: I'm not here just to burn calories.

#### TimFox

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##### Re: Physics Question - ma = mg
« Reply #155 on: July 26, 2021, 03:38:40 pm »
The answer for calories burned by different physical exercise routines is not to be found in physics, but in physiology.

#### RJHayward

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##### Re: Physics Question - ma = mg
« Reply #156 on: July 26, 2021, 05:51:53 pm »
As to the question, about finding an equivalence between calories for an hour lifting weights VS an hour on treadmill, I recall watching a researcher monitoring a face mask, breathing hose. I think the scientists use the oxygen consumption to get parameters related to calories consumed. My guess, also, is there might be some other processes...ie Pathelogical that allow short bursts (of physical performance) in absence of correlation with oxygen consumption.
Oxygen consumption, my speculation, would be able to be directly correlated, with the whole cellular energy equation, almost literally molecule by molecule.
I think there must be ways of answering your question, assuming you get all the circumstances for comparing the two excercise activities.
For a similar reasoning, I probably would not look at a person's body weight (changes), as that could get complex. My guess is that body water loss, sweat, would make exact calorie studies hard to control, just solely on gross weight.
Perhaps, there are military conducted studies, that would supply those performance comparisons.
- Rick B

#### CatalinaWOW

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##### Re: Physics Question - ma = mg
« Reply #157 on: July 26, 2021, 07:40:56 pm »
Bostonman, don't take this negatively, but you are on a fool's errand.  I am not challenging your intelligence or your knowledge of physics or your ability to learn.  I am sure that after enough work and study you could separate out the actual work performed in the two activities (note that in the pure physics sense neither involves any work since the runner on the treadmill ends in the same state he began, and the weights also return to their original position).  Work being defined as the integral of the scalar force*distance for the two activities.  You can sort out all of the inefficiencies in the biological production of that force and distance.  Determine the base consumption and the changes in base consumption due to the activity.  Figure out how to adjust for the differences in size and physiology between you and the guy you are comparing with.  And in the end it will mean nothing.  The other guy won't be convinced, and you probably won't either unless the answer turns out in your favor.

The only real answer when dealing with a question of the type you are discussing is what works for you.  Which has little or nothing to do with physics.  And which answer trumps all the gym instructors, exercise books and other advice on the subject.

#### bostonman

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##### Re: Physics Question - ma = mg
« Reply #158 on: July 27, 2021, 02:57:44 am »
I wouldn't and didn't get offended at all.

This thread seemed to turn into more general conversation about everyday physics and maybe I got too comfortable tossing out questions. You're correct, I'm sure I can open plenty of physics and body training books, but sometimes just talking to people helps weed out the confusion. Books go only so far which can sometimes cause limitations in learning.

In some cases this thread went way beyond general mass and acceleration, and other times it seemed to be just general discussion that helped clear confusion.

It's possible I just got too comfortable continuing to talk thinking it was all general discussion while others were providing answers in hopes of ending the thread with a final answer.

#### CatalinaWOW

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##### Re: Physics Question - ma = mg
« Reply #159 on: July 27, 2021, 03:42:48 am »
If you want an interesting example of everyday physics think of driving a car.  Moving along at constant speed you approach a stop sign.  What is the optimum braking profile?

First step, define optimum.  Shortest arrival time?  Constant deceleration?  Minimum jerk?

The, assuming brake friction is constant over time and wheel rotation speed, what pressure profile is required to achieve it.

Simple problem with much meat.

#### bostonman

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##### Re: Physics Question - ma = mg
« Reply #160 on: July 28, 2021, 03:25:00 am »
If anyone cares, I had a real world discussion at the gym today about lifting weights.

A few guys were doing lat pull downs and someone asked the other guy why he can do a pull up, but, he can't do equal weight on a lat pull down machine.

I chimed in stating I've had similar thoughts because many people can do a pull up which involves lifting their own body weight, however, they can't pull down an equal amount.

We concluded that many factors come into play such as slightly swinging the body, and, more muscles are being used for a pull up.

Anyway, thought everyone would get a chuckle out of this story.

#### bostonman

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##### Re: Physics Question - ma = mg
« Reply #161 on: July 31, 2021, 01:45:28 pm »

While I've asked certain basic physics questions, or maybe I assume they are basic, and I can certainly find formulas in a book, I find that discussing certain aspects offers much more than books some time.

At least for me, sometimes putting it all together doesn't come natural. While simply picking up an object is physics 101, getting down to the deep details that some responses were, or simply analogies connecting everyday real life stuff, really makes (at least myself) see common tasks in a different light.

Smf