Power vs Energy
Replies
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robertw486 wrote: »robertw486 wrote: »
If the power vs energy equation were always a constant, it wouldn't matter. But they are not. I'd challenge you to provide any example of a mechanical device in operation that could be driven by any selection of engine or motor and be equally efficient. It won't exist.
@blambo61
See the above. I think this is where the flaw in your reasoning is. Even in real world situations with machines, efficiency is a key. And those machines can be turned off. Humans don't turn off.
Power is always the time derivative of energy. Final energy is always the integral over time of power plus the initial energy level. Not sure I understand what you're saying.0 -
robertw486 wrote: »robertw486 wrote: »
If the power vs energy equation were always a constant, it wouldn't matter. But they are not. I'd challenge you to provide any example of a mechanical device in operation that could be driven by any selection of engine or motor and be equally efficient. It won't exist.
@blambo61
See the above. I think this is where the flaw in your reasoning is. Even in real world situations with machines, efficiency is a key. And those machines can be turned off. Humans don't turn off.
Power is always the time derivative of energy. Final energy is always the integral over time of power plus the initial energy level. Not sure I understand what you're saying.
In regards to the human body, or even in mechanical terms, I can't agree with that.
The total power or energy required to complete a task is set. For the sake of discussion remove all variables that exist in humans regarding composition, weight, stride lengths, etc and consider you and myself exact human models in the basic physical sense. If we run X miles at Y speed we would consume Z calories to perform that task. Just as with machines the power required to do the task would be equal.
BUT just as with machines the energy source must be considered. If as an engineer, you had to provide a recommendation to power a conveyor belt with a constant load of 2 HP, would you choose and electric motor with that load range in mind, or would you choose a large diesel engine? Though the power required to do the job would be constant, one power source would be more energy efficient than the other.
In the human body, the systems are complex enough that we would probably have to view it in terms of a cutting edge hybrid energy system, with power of various efficiency levels derived from differing physical components, all of which could be influenced to some degree by the fuels (food) we consume, and all of which have different limitations.
And as I said, you can't turn the human body off. So while I agree that within reason the energy required by two people very similar in build and such would be essentially the same, the energy they consume through a day could be grossly different due to BMR, and everything that influences BMR. With so many complex systems in place even modern science doesn't have all the answers to BMR. As an example, both the liver and the brain usually consume more energy in the average human than muscle does. So if two people were the same physical sizes, exercised the same, ate the same... etc, and one of then for whatever reason had a more efficient liver process, that person would consume less energy hour to hour every day.0 -
CoffeeNCardio wrote: »If a person walks a certain distance, the energy expended getting there is the same no matter how fast you go to get there. If you get someplace fast, the power level you operated at to get there was higher than if you went slower but the energy expended (cals) is the same whether you go fast or slow.
How does going faster help us then in loosing cals? I think the answer is that the higher power levels required for going faster (or lifting heavier) will increase our base metabolism rate. I'm not sure how that works but maybe going faster helps develop bigger mitochondria to handle the power levels required to go faster which then require more energy to function when peak loads are not placed on them thus upping the bmr. Any biologists out there to explain?
Erm.... no, not even a little bit. To get someplace faster, you expend MORE energy because you worked harder than the slower pace. Because you had to fight gravity harder, your muscles required more oxygen and your body put off more heat, your heart rate had to increase. All the things that happen when one exercises. If you burned 300 calories going from point A to point B at 3.0 mph, you're for sure gonna burn more than that going from point A to point B at 6.5 mph. Jogging is harder than walking, and thus, you expend more energy putting out the extra effort to increase your speed.
ETA: In case there's about to be an argument about walking, this is still the case. More effort is required to walk at 4 mph than to walk at 2.5 mph.
Sorry, but I'm an engineer and understand energy and power very well. I don't know biology very well. If you go 10miles/hr for 30 min you go five miles. If you go 5miles/hr for and 1 hr, you go five miles. Both will expend the same energy (Energy=Force x Distance). You will have been operating at a higher power setting (Power=Force x Velocity) when you go faster but for only 1/2 the time with my example. The energy expended is the same for both. I'm not including small factors like wind resistance or heat expended.
Effort at a given instant is associated with your power level. Effort over time or distance is associated with energy expended.
You didn't mention halving the time in your original example. You only said "If a person walks a certain distance, the energy expended getting there is the same no matter how fast you go to get there."
So what I said still stands. I burn more calories walking 3 miles at 4.0 mph than walking that exact same distance at 2.5 mph. My body requires more energy to increase my speed, and thus it burns more.
Further, even with halving the time as for your example, like let's say 3 mph for one hour versus 6.0mph for 30 mins. Yes, I have gone the same distance (3.0 miles) but going 6.0 miles per hour is a RUN. Running expends more energy. Burns more calories. It requires more effort, my muscles have to work harder, my heart rate must increase. And while it's fine to blow off wind resistance in this calculation (because hey treadmills, wind isn't even a factor there so that's not wrong), it is not appropriate to ignore heat output, as burning calories is heat output. Calories are a measurement of approximately the amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius. It's thermodynamics, which is what is used to measure human energy expenditure when it comes to calorie counting.0 -
robertw486 wrote: »robertw486 wrote: »robertw486 wrote: »
If the power vs energy equation were always a constant, it wouldn't matter. But they are not. I'd challenge you to provide any example of a mechanical device in operation that could be driven by any selection of engine or motor and be equally efficient. It won't exist.
@blambo61
See the above. I think this is where the flaw in your reasoning is. Even in real world situations with machines, efficiency is a key. And those machines can be turned off. Humans don't turn off.
Power is always the time derivative of energy. Final energy is always the integral over time of power plus the initial energy level. Not sure I understand what you're saying.
In regards to the human body, or even in mechanical terms, I can't agree with that.
The total power or energy required to complete a task is set. For the sake of discussion remove all variables that exist in humans regarding composition, weight, stride lengths, etc and consider you and myself exact human models in the basic physical sense. If we run X miles at Y speed we would consume Z calories to perform that task. Just as with machines the power required to do the task would be equal.
BUT just as with machines the energy source must be considered. If as an engineer, you had to provide a recommendation to power a conveyor belt with a constant load of 2 HP, would you choose and electric motor with that load range in mind, or would you choose a large diesel engine? Though the power required to do the job would be constant, one power source would be more energy efficient than the other.
In the human body, the systems are complex enough that we would probably have to view it in terms of a cutting edge hybrid energy system, with power of various efficiency levels derived from differing physical components, all of which could be influenced to some degree by the fuels (food) we consume, and all of which have different limitations.
And as I said, you can't turn the human body off. So while I agree that within reason the energy required by two people very similar in build and such would be essentially the same, the energy they consume through a day could be grossly different due to BMR, and everything that influences BMR. With so many complex systems in place even modern science doesn't have all the answers to BMR. As an example, both the liver and the brain usually consume more energy in the average human than muscle does. So if two people were the same physical sizes, exercised the same, ate the same... etc, and one of then for whatever reason had a more efficient liver process, that person would consume less energy hour to hour every day.
I would say he is correct because those are the definitions of power and energy.
The issue is that you can't always write them as functions that you can take the definitive integral or derivative of - instead you'd need to do an approximation.
For example, take what is a mechanical system - a waterwheel with a dozen buckets with water, and the buckets tilt to drop water on each other - such that the system sometimes reverses direction. Under certain conditions of reversal, the system is chaotic function that is non-differentiable. Yet clearly we know the wheel has some level of energy as the amount of water in buckets changing heights represents various levels of potential energy.0 -
robertw486 wrote: »robertw486 wrote: »robertw486 wrote: »
If the power vs energy equation were always a constant, it wouldn't matter. But they are not. I'd challenge you to provide any example of a mechanical device in operation that could be driven by any selection of engine or motor and be equally efficient. It won't exist.
@blambo61
See the above. I think this is where the flaw in your reasoning is. Even in real world situations with machines, efficiency is a key. And those machines can be turned off. Humans don't turn off.
Power is always the time derivative of energy. Final energy is always the integral over time of power plus the initial energy level. Not sure I understand what you're saying.
In regards to the human body, or even in mechanical terms, I can't agree with that.
The total power or energy required to complete a task is set. For the sake of discussion remove all variables that exist in humans regarding composition, weight, stride lengths, etc and consider you and myself exact human models in the basic physical sense. If we run X miles at Y speed we would consume Z calories to perform that task. Just as with machines the power required to do the task would be equal.
BUT just as with machines the energy source must be considered. If as an engineer, you had to provide a recommendation to power a conveyor belt with a constant load of 2 HP, would you choose and electric motor with that load range in mind, or would you choose a large diesel engine? Though the power required to do the job would be constant, one power source would be more energy efficient than the other.
In the human body, the systems are complex enough that we would probably have to view it in terms of a cutting edge hybrid energy system, with power of various efficiency levels derived from differing physical components, all of which could be influenced to some degree by the fuels (food) we consume, and all of which have different limitations.
And as I said, you can't turn the human body off. So while I agree that within reason the energy required by two people very similar in build and such would be essentially the same, the energy they consume through a day could be grossly different due to BMR, and everything that influences BMR. With so many complex systems in place even modern science doesn't have all the answers to BMR. As an example, both the liver and the brain usually consume more energy in the average human than muscle does. So if two people were the same physical sizes, exercised the same, ate the same... etc, and one of then for whatever reason had a more efficient liver process, that person would consume less energy hour to hour every day.
The relationship between power and energy as I described is true always for all systems.
Power isn't energy. The "total power set to complete a task is set" isnt a true statement. You can get to pount b from point a going different speeds. The power levels will vary based on speed. That applies to machines and people.
The rest of what you said I agree with.
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So Superman isn't flying, he's running?0 -
Ooops, yeah. For a fraction of a second, no feet on the ground. Duh.
The energy expenditure would be more, wouldn't it, if a runner is also going higher (counteracting the force of gravity) as well as going forward?
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CoffeeNCardio wrote: »CoffeeNCardio wrote: »If a person walks a certain distance, the energy expended getting there is the same no matter how fast you go to get there. If you get someplace fast, the power level you operated at to get there was higher than if you went slower but the energy expended (cals) is the same whether you go fast or slow.
How does going faster help us then in loosing cals? I think the answer is that the higher power levels required for going faster (or lifting heavier) will increase our base metabolism rate. I'm not sure how that works but maybe going faster helps develop bigger mitochondria to handle the power levels required to go faster which then require more energy to function when peak loads are not placed on them thus upping the bmr. Any biologists out there to explain?
Erm.... no, not even a little bit. To get someplace faster, you expend MORE energy because you worked harder than the slower pace. Because you had to fight gravity harder, your muscles required more oxygen and your body put off more heat, your heart rate had to increase. All the things that happen when one exercises. If you burned 300 calories going from point A to point B at 3.0 mph, you're for sure gonna burn more than that going from point A to point B at 6.5 mph. Jogging is harder than walking, and thus, you expend more energy putting out the extra effort to increase your speed.
ETA: In case there's about to be an argument about walking, this is still the case. More effort is required to walk at 4 mph than to walk at 2.5 mph.
Sorry, but I'm an engineer and understand energy and power very well. I don't know biology very well. If you go 10miles/hr for 30 min you go five miles. If you go 5miles/hr for and 1 hr, you go five miles. Both will expend the same energy (Energy=Force x Distance). You will have been operating at a higher power setting (Power=Force x Velocity) when you go faster but for only 1/2 the time with my example. The energy expended is the same for both. I'm not including small factors like wind resistance or heat expended.
Effort at a given instant is associated with your power level. Effort over time or distance is associated with energy expended.
You didn't mention halving the time in your original example. You only said "If a person walks a certain distance, the energy expended getting there is the same no matter how fast you go to get there."
So what I said still stands. I burn more calories walking 3 miles at 4.0 mph than walking that exact same distance at 2.5 mph. My body requires more energy to increase my speed, and thus it burns more.
Further, even with halving the time as for your example, like let's say 3 mph for one hour versus 6.0mph for 30 mins. Yes, I have gone the same distance (3.0 miles) but going 6.0 miles per hour is a RUN. Running expends more energy. Burns more calories. It requires more effort, my muscles have to work harder, my heart rate must increase. And while it's fine to blow off wind resistance in this calculation (because hey treadmills, wind isn't even a factor there so that's not wrong), it is not appropriate to ignore heat output, as burning calories is heat output. Calories are a measurement of approximately the amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius. It's thermodynamics, which is what is used to measure human energy expenditure when it comes to calorie counting.
If you go the same distance but go different speeds by definition the time to get there will be different.
I agree you will burn more cals at the higher speed but not for the reason you mentioned. Speed will cause the need for more calories due to other things changing due to the increased speed but not directly just due to the speed change. In your definition of a calorie, there is no requirement for how fast the water changes a degree by absorbing the calorie of energy. I've studied this in physics, two formal thermodynamics classes, a physical system dynamics class, and several others as well as doing some of this at work.
Also, all the energy hasn't been turned to body heat. A lot is lost in friction with the road. Yes running will consume more than walking for various reasons a big one being the extra vertical distance moved while leaving the ground.0 -
Ooops, yeah. For a fraction of a second, no feet on the ground. Duh.
The energy expenditure would be more, wouldn't it, if a runner is also going higher (counteracting the force of gravity) as well as going forward?
You are correct. The energy is lost when you hit the ground due to friction, from heating the air due to friction, and heat dissapated out the body.0 -
robertw486 wrote: »robertw486 wrote: »robertw486 wrote: »
If the power vs energy equation were always a constant, it wouldn't matter. But they are not. I'd challenge you to provide any example of a mechanical device in operation that could be driven by any selection of engine or motor and be equally efficient. It won't exist.
@blambo61
See the above. I think this is where the flaw in your reasoning is. Even in real world situations with machines, efficiency is a key. And those machines can be turned off. Humans don't turn off.
Power is always the time derivative of energy. Final energy is always the integral over time of power plus the initial energy level. Not sure I understand what you're saying.
In regards to the human body, or even in mechanical terms, I can't agree with that.
The total power or energy required to complete a task is set. For the sake of discussion remove all variables that exist in humans regarding composition, weight, stride lengths, etc and consider you and myself exact human models in the basic physical sense. If we run X miles at Y speed we would consume Z calories to perform that task. Just as with machines the power required to do the task would be equal.
BUT just as with machines the energy source must be considered. If as an engineer, you had to provide a recommendation to power a conveyor belt with a constant load of 2 HP, would you choose and electric motor with that load range in mind, or would you choose a large diesel engine? Though the power required to do the job would be constant, one power source would be more energy efficient than the other.
In the human body, the systems are complex enough that we would probably have to view it in terms of a cutting edge hybrid energy system, with power of various efficiency levels derived from differing physical components, all of which could be influenced to some degree by the fuels (food) we consume, and all of which have different limitations.
And as I said, you can't turn the human body off. So while I agree that within reason the energy required by two people very similar in build and such would be essentially the same, the energy they consume through a day could be grossly different due to BMR, and everything that influences BMR. With so many complex systems in place even modern science doesn't have all the answers to BMR. As an example, both the liver and the brain usually consume more energy in the average human than muscle does. So if two people were the same physical sizes, exercised the same, ate the same... etc, and one of then for whatever reason had a more efficient liver process, that person would consume less energy hour to hour every day.
I would say he is correct because those are the definitions of power and energy.
The issue is that you can't always write them as functions that you can take the definitive integral or derivative of - instead you'd need to do an approximation.
For example, take what is a mechanical system - a waterwheel with a dozen buckets with water, and the buckets tilt to drop water on each other - such that the system sometimes reverses direction. Under certain conditions of reversal, the system is chaotic function that is non-differentiable. Yet clearly we know the wheel has some level of energy as the amount of water in buckets changing heights represents various levels of potential energy.
There will not be a closed form solution to the integrals due to the complexity of the model as you stated but it could be easily numerically integrated using simple forward, backards, central, trapazoidal, runga-cutta, ect. algorithms as long as you have access to all inputs needed for the integration, if not, you may have to design an observer to estimate the states.
For this problem, you wouldn't be differentiating and would be integrating so discontinuities you mentioned wouldn't matter. For some systems with rotating reference frames, your integral can blow up due to divide by zeros which are handled for some situations using quaternions. Video games and some aircraft simulators do that.
That's about all I've got to say about that!0 -
robertw486 wrote: »robertw486 wrote: »robertw486 wrote: »
If the power vs energy equation were always a constant, it wouldn't matter. But they are not. I'd challenge you to provide any example of a mechanical device in operation that could be driven by any selection of engine or motor and be equally efficient. It won't exist.
@blambo61
See the above. I think this is where the flaw in your reasoning is. Even in real world situations with machines, efficiency is a key. And those machines can be turned off. Humans don't turn off.
Power is always the time derivative of energy. Final energy is always the integral over time of power plus the initial energy level. Not sure I understand what you're saying.
In regards to the human body, or even in mechanical terms, I can't agree with that.
The total power or energy required to complete a task is set. For the sake of discussion remove all variables that exist in humans regarding composition, weight, stride lengths, etc and consider you and myself exact human models in the basic physical sense. If we run X miles at Y speed we would consume Z calories to perform that task. Just as with machines the power required to do the task would be equal.
BUT just as with machines the energy source must be considered. If as an engineer, you had to provide a recommendation to power a conveyor belt with a constant load of 2 HP, would you choose and electric motor with that load range in mind, or would you choose a large diesel engine? Though the power required to do the job would be constant, one power source would be more energy efficient than the other.
In the human body, the systems are complex enough that we would probably have to view it in terms of a cutting edge hybrid energy system, with power of various efficiency levels derived from differing physical components, all of which could be influenced to some degree by the fuels (food) we consume, and all of which have different limitations.
And as I said, you can't turn the human body off. So while I agree that within reason the energy required by two people very similar in build and such would be essentially the same, the energy they consume through a day could be grossly different due to BMR, and everything that influences BMR. With so many complex systems in place even modern science doesn't have all the answers to BMR. As an example, both the liver and the brain usually consume more energy in the average human than muscle does. So if two people were the same physical sizes, exercised the same, ate the same... etc, and one of then for whatever reason had a more efficient liver process, that person would consume less energy hour to hour every day.
I would say he is correct because those are the definitions of power and energy.
The issue is that you can't always write them as functions that you can take the definitive integral or derivative of - instead you'd need to do an approximation.
For example, take what is a mechanical system - a waterwheel with a dozen buckets with water, and the buckets tilt to drop water on each other - such that the system sometimes reverses direction. Under certain conditions of reversal, the system is chaotic function that is non-differentiable. Yet clearly we know the wheel has some level of energy as the amount of water in buckets changing heights represents various levels of potential energy.
There will not be a closed form solution to the integrals due to the complexity of the model as you stated but it could be easily numerically integrated using simple forward, backards, central, trapazoidal, runga-cutta, ect. algorithms as long as you have access to all inputs needed for the integration, if not, you may have to design an observer to estimate the states.
For this problem, you wouldn't be differentiating and would be integrating so discontinuities you mentioned wouldn't matter. For some systems with rotating reference frames, your integral can blow up due to divide by zeros which are handled for some situations using quaternions. Video games and some aircraft simulators do that.
That's about all I've got to say about that!
Fractals can't be integrated either. Yes, you can do numerics on them, but for a chaotic system like the Lorenz waterwheel any failure in reading initial conditions will lead to radically different results.0 -
CoffeeNCardio wrote: »CoffeeNCardio wrote: »If a person walks a certain distance, the energy expended getting there is the same no matter how fast you go to get there. If you get someplace fast, the power level you operated at to get there was higher than if you went slower but the energy expended (cals) is the same whether you go fast or slow.
How does going faster help us then in loosing cals? I think the answer is that the higher power levels required for going faster (or lifting heavier) will increase our base metabolism rate. I'm not sure how that works but maybe going faster helps develop bigger mitochondria to handle the power levels required to go faster which then require more energy to function when peak loads are not placed on them thus upping the bmr. Any biologists out there to explain?
Erm.... no, not even a little bit. To get someplace faster, you expend MORE energy because you worked harder than the slower pace. Because you had to fight gravity harder, your muscles required more oxygen and your body put off more heat, your heart rate had to increase. All the things that happen when one exercises. If you burned 300 calories going from point A to point B at 3.0 mph, you're for sure gonna burn more than that going from point A to point B at 6.5 mph. Jogging is harder than walking, and thus, you expend more energy putting out the extra effort to increase your speed.
ETA: In case there's about to be an argument about walking, this is still the case. More effort is required to walk at 4 mph than to walk at 2.5 mph.
Sorry, but I'm an engineer and understand energy and power very well. I don't know biology very well. If you go 10miles/hr for 30 min you go five miles. If you go 5miles/hr for and 1 hr, you go five miles. Both will expend the same energy (Energy=Force x Distance). You will have been operating at a higher power setting (Power=Force x Velocity) when you go faster but for only 1/2 the time with my example. The energy expended is the same for both. I'm not including small factors like wind resistance or heat expended.
Effort at a given instant is associated with your power level. Effort over time or distance is associated with energy expended.
You didn't mention halving the time in your original example. You only said "If a person walks a certain distance, the energy expended getting there is the same no matter how fast you go to get there."
So what I said still stands. I burn more calories walking 3 miles at 4.0 mph than walking that exact same distance at 2.5 mph. My body requires more energy to increase my speed, and thus it burns more.
Further, even with halving the time as for your example, like let's say 3 mph for one hour versus 6.0mph for 30 mins. Yes, I have gone the same distance (3.0 miles) but going 6.0 miles per hour is a RUN. Running expends more energy. Burns more calories. It requires more effort, my muscles have to work harder, my heart rate must increase. And while it's fine to blow off wind resistance in this calculation (because hey treadmills, wind isn't even a factor there so that's not wrong), it is not appropriate to ignore heat output, as burning calories is heat output. Calories are a measurement of approximately the amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius. It's thermodynamics, which is what is used to measure human energy expenditure when it comes to calorie counting.
If you go the same distance but go different speeds by definition the time to get there will be different.
I agree you will burn more cals at the higher speed but not for the reason you mentioned. Speed will cause the need for more calories due to other things changing due to the increased speed but not directly just due to the speed change. In your definition of a calorie, there is no requirement for how fast the water changes a degree by absorbing the calorie of energy. I've studied this in physics, two formal thermodynamics classes, a physical system dynamics class, and several others as well as doing some of this at work.
Also, all the energy hasn't been turned to body heat. A lot is lost in friction with the road. Yes running will consume more than walking for various reasons a big one being the extra vertical distance moved while leaving the ground.
You're still applying mechanical energy as the differentiator in a chemical system. Running and other high output activity will involve generating chemical reactions which need to use chemicals past their normal reaction rates. It also then requires additional output to keep homeostasis in related systems, like having to dissipate the excess heat.0 -
Ooops, yeah. For a fraction of a second, no feet on the ground. Duh.
The energy expenditure would be more, wouldn't it, if a runner is also going higher (counteracting the force of gravity) as well as going forward?
Reckon so. Most of the mechanical energy is probably the up and down part (changing potential energy).
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thorsmom01 wrote: »juggernaut1974 wrote: »I purposely posted this knowing how the power and energy thing worked to get people to think and also to get feedback on why it will overall be better to go faster on the biological level (assuming you don't get injured).
Biology and engineering aren't really related. To move faster a person has to convert ATP into ADP at a higher rate.
Power is the rate of energy. You are talking about power. Biological systems have mass and are moved by forces. They do relate in this context.
No, they really don't. We aren't machines.
We have no mass and don't respond to forces?
Yes, but we aren't simple machines. We aren't talking about a hypothetical single force pushing a stationary box up a frictionless inclined plane at a constant rate of acceleration in a vacuum here.
Running (for example) increases heart rate more than walking (for example), so more heart beats = more energy spent. More breaths taken by the lungs = more energy spent. Maybe a glycogen spike is needed ...more digestion...more energy. There are probably other body systems and functions as well that will speed up and increase energy burn when vigorously exercising vs. walking at a moderate pace.
Speak for yourself. I'm indeed a simple machine. I eat and lift. Eat and lift. You can come check my abs of steel if you don't believe me ( they are made of steel , because I am a machine ) Lmao !!
@thorsmom01
The temporary closing of this thread somehow allowed me to miss your above post. Though I can argue and debate with the best of them, signing up for abs of steel inspection would have surely distracted me from the post. Just PM me the details of how this inspection thing works, and consider my contributions to this forum done!0 -
Coursera has free MOOCs for all--college level courses. Many from Ivy League schools and world-renown faculty. They offer everything being discussed here.0
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