Understanding Physics -- in which way?

[adjurovich]

I’ve heard at least a million times that you need to understand physics, but never actually understood in which way? When I study, I understand what the textbook says and how to apply it. But questioning why is it the way it is, usually confuses me and many times leaves me uncertain, I doubt it I could prove why some things work the way they do. I have really well experience with maths I understand how the subject works. I feel satisfied with my understanding only when I can prove why something works. But when it comes to physics I am not able to do so many times. I need advising because it discourages me many times and keeps me confused whether or not I’m on the right track

 

[Haborix]

The why problem of physics is, in my mind, equivalent to asking why about the axioms in mathematics. However, in physics, nature "chooses" the axioms while in mathematics they are chosen by us. I think we all have a fundamental yearning for the why, and it is left to each of us to personally decide, subject to the constraints of nature, when we are satisfied.

 

[symbolipoint]

I’ve heard at least a million times that you need to understand physics, but never actually understood in which way? When I study, I understand what the textbook says and how to apply it. But questioning why is it the way it is, usually confuses me and many times leaves me uncertain, I doubt it I could prove why some things work the way they do. I have really well experience with maths I understand how the subject works. I feel satisfied with my understanding only when I can prove why something works. But when it comes to physics I am not able to do so many times. I need advising because it discourages me many times and keeps me confused whether or not I’m on the right track

One can ask one or two or both kinds of questions: How? and Why? Either you decide, or someone else decide for you, which of those questions to find answers for. You find and read about the relevant acting laws for the Physics topics you study; and you can certainly become confused. Continued review and practice is what is needed to reduce (but often not completely eliminate) this confusion.

 

[adjurovich]

One can ask one or two or both kinds of questions: How? and Why? Either you decide, or someone else decide for you, which of those questions to find answers for. You find and read about the relevant acting laws for the Physics topics you study; and you can certainly become confused. Continued review and practice is what is needed to reduce (but often not completely eliminate) this confusion.

You’re right about that. But what really annoys me is the fact that I can’t find answers to the questions I ask. For example it was said that Tension is the only force acting on pulley and it exerts torque. I asked how can a force that pulls bodies exert torque on pulley? And there is no answer in textbook, I searched in another and couldn’t find it. And these things usually make me question whether something with my understanding is wrong. I am mostly self taught and have not been really good at physics when I studied it in primary school because I seemed disinterested due to having a really bad teacher and rarely ever studied it. So it’s been around few months since I tried truly studying for the first time and things don’t really go as smooth as I expected they will.

 

[symbolipoint]

You’re right about that. But what really annoys me is the fact that I can’t find answers to the questions I ask. For example it was said that Tension is the only force acting on pulley and it exerts torque. I asked how can a force that pulls bodies exert torque on pulley? And there is no answer in textbook, I searched in another and couldn’t find it. And these things usually make me question whether something with my understanding is wrong. I am mostly self taught and have not been really good at physics when I studied it in primary school because I seemed disinterested due to having a really bad teacher and rarely ever studied it. So it’s been around few months since I tried truly studying for the first time and things don’t really go as smooth as I expected they will.

Not clear exactly what your age is but I expect you are very young. You would find far more success if you truly begin studying at, for example, a community college, or maybe at a university. Why I say this? Requirement to LEARN Algebra, Trigonometry, and some Calculus first; Good (or better ) instruction for the Physics from people who have real Physics education themselves.

Still the necessity to study, do exercise problems, restudy, review, and tolerate some confusion as part of the learning process are necessary. Laboratory exercises will also be assigned and are needed.

 

[adjurovich]

Not clear exactly what your age is but I expect you are very young. You would find far more success if you truly begin studying at, for example, a community college, or maybe at a university. Why I say this? Requirement to LEARN Algebra, Trigonometry, and some Calculus first; Good (or better ) instruction for the Physics from people who have real Physics education themselves.

Still the necessity to study, do exercise problems, restudy, review, and tolerate some confusion as part of the learning process are necessary. Laboratory exercises will also be assigned and are needed.

I’m 16 right now but since I am not from the US, educational system here is little different and we go to faculty at 19. So I’m technically second year of high school here. I self taught myself some mathematics: technically some basic calculus and it wasn’t so hard to me - very entertaining to be honest. Also I am doing pretty well at trigonometry and algebra. What I hate the most is the fact that I never know am I going in a good direction or I lack talent / abilities. I was never one of these “smart” tutored kids from the early age because I lacked interest in maths. But I remember being very interested in science when I was really young - especially physics and chemistry. Still being a curious kid has nothing to do with abilities. My main problem is that I can understand the textbook material yet I cannot explain “why is it that way” if someone asked me - since there are usually no such explanations or even questions in textbook. I always have the additional questions that I can’t find answers for.

 

[gmax137]

For example it was said that Tension is the only force acting on pulley and it exerts torque.

I'm not sure why you don't get this. The tension in the rope exerts a force on the rim of the pulley, which is free to rotate about its spindle. This is really the definition of torque -- A force applied perpendicularly to a lever multiplied by its distance from the lever's fulcrum (the length of the lever arm) is its torque. [wiki]

There are a few assumptions built in: the rope doesn't slip, no friction at the spindle, ...

The best way to bring this home is to do a bunch of problems that involve torque in the solution. Eventually you will see why it is a useful concept.

 

[Ben2]

To my limited understanding (sub-2 physics average), there's such a thing as over-analysis. This student needs to accept that any model of the physical world is subject to both inaccuracies and "off the deep end" predictions. Besides the recommendations above, I suggest reading some history of science.

 

[Mark44]

But questioning why is it the way it is, usually confuses me and many times leaves me uncertain

Take a look at this video of an interview with Richard Feynman:
Richard Feynman on Magnets and Why Questions

 

[symbolipoint]

Take a look at this video of an interview with Richard Feynman:
Richard Feynman on Magnets and Why Questions

That video is not available anymore; or at least not available at the address there.
Let's try a youtube search, "Richard Feynman on Magnets and Why Questions" and see what can be found.

Here we go......

 

[Lnewqban]

For example it was said that Tension is the only force acting on pulley and it exerts torque. I asked how can a force that pulls bodies exert torque on pulley? And there is no answer in textbook, I searched in another and couldn’t find it. And these things usually make me question whether something with my understanding is wrong.

We are all here to help you understand, all you need to do is to keep asking questions until you deeply understand any subject.

A pulley is nothing more than many levers sharing a common pivot point.

 

[adjurovich]

We are all here to help you understand, all you need to do is to keep asking questions until you deeply understand any subject.

A pulley is nothing more than many levers sharing a common pivot point.

View attachment 346027

I understood that tension appears in rope when it’s under some stress (some block pulls it for example) on one end and acts in a way to pull object (of course rope cannot push) - the rope exerts this force on objects attached to it. Now if I got it right, the entire system along with rope accelerates in one direction but there is static friction between pulley and the rope that tries to oppose the relative motion and acts on rope, but also the rope exerts tension on pulley in the opposite direction (which in this case is the direction the entire system is moving). This may be a little off-topic tho?

The only complaint I’ve made in one of my threads is that there is nothing about it mentioned in several textbooks I’ve checked. How is the student supposed to conclude all?

 

[Lnewqban]

Now if I got it right, the entire system along with rope accelerates in one direction but there is static friction between pulley and the rope that tries to oppose the relative motion and acts on rope, but also the rope exerts tension on pulley in the opposite direction (which in this case is the direction the entire system is moving).

That static friction impedes any relative sliding of the rope over the pulley (it simplifies the problem as tangential velocities of rope and pulley are equal), but it does not consume any energy or interferes with the acceleration of the system.

High friction in the shaft or axle of the pulley would, reason for which is minimized or considered irrelevant.

The only complaint I’ve made in one of my threads is that there is nothing about it mentioned in several textbooks I’ve checked. How is the student supposed to conclude all?

I would include at least a brief explanation, but I am far from a book author.

Once the basic principles are solid in your mind, combining those is just a matter of practice.

In the case of our pulley, we have the principles of friction, levers, forces and accelerations to play with.

Don't get discouraged, others have learned via poorly written books, you also can.

 

[adjurovich]

That static friction impedes any relative sliding of the rope over the pulley (it simplifies the problem as tangential velocities of rope and pulley are equal), but it does not consume any energy or interferes with the acceleration of the system.

High friction in the shaft or axle of the pulley would, reason for which is minimized or considered irrelevant.


I would include at least a brief explanation, but I am far from a book author.

Once the basic principles are solid in your mind, combining those is just a matter of practice.

In the case of our pulley, we have the principles of friction, levers, forces and accelerations to play with.

Don't get discouraged, others have learned via poorly written books, you also can.

Thanks for help!! I get it now!