Why is Physics So Hard? Advice to Improve

[nobahar]

Physics is not a formula-based activity. You can't memorize your way through physics like you can with chemistry, biology and the like. You have to understand the conceptual difficulties in the problem, then translate that concept into another language: Mathematics.

Your referring to Secondary school Biology and Chemistry, right?

 

[Vectronix]

Mathematics is entirely arbitrary. It does not dictate physical phenomena. However, it's used by physicists as a language to describe physical phenomena quantitatively very precisely. Someone can understand Newton's Laws qualitatively but not be able to express it quantitatively. That's my distinction - a very fine one, I know.

When doing physics problems the maths is physics, if you don't understand that maths then you don't understand the physics.

I agree with both of you simultaneously. :P

I actually think the higher the level of math, the easier math gets. It would have been nice to understand all the math when I took all of my physics classes in school.

 

[nlsherrill]

It's not physics or math that's hard. What's hard is setting up the problem. You can run through disgustingly long and complicated integrals like they were 1+1, and still get knocked on your butt by physics math that is often simple arithmetic.

Physics is not a formula-based activity. You can't memorize your way through physics like you can with chemistry, biology and the like. You have to understand the conceptual difficulties in the problem, then translate that concept into another language: Mathematics.

Yes, and generally this is fitting to a physics problem. Setting up the problem IS the physics. Setting it up is recognizing which physical laws are/are not conserved, where your limits extend, etc, and then developing a mathematical model to represent it. And this is why physics is hard, because you have to come up with a clever way to even get started on some problems.

I think we are on the same page, but in my opinion "setting up the problem" is the physics part of the problem.

 

[Ryker]

How didn't you take that meaning from my post?

I thought you agreed with the part of Angry Citizen's post that said

"It's not physics or math that's hard."

I guess I should've quoted him instead then.

Yes, and generally this is fitting to a physics problem. Setting up the problem IS the physics. Setting it up is recognizing which physical laws are/are not conserved, where your limits extend, etc, and then developing a mathematical model to represent it. And this is why physics is hard, because you have to come up with a clever way to even get started on some problems.

I think we are on the same page, but in my opinion "setting up the problem" is the physics part of the problem.

And yeah, this is what I meant.

 

[Shackleford]

I thought you agreed with the part of Angry Citizen's post that said
I guess I should've quoted him instead then.
And yeah, this is what I meant.

Oh, sorry.

I was agreeing with

What's hard is setting up the problem.

Setting up the problem is math and physics.

 

[Angry Citizen]

I tend to differentiate the three. Math, fundamentally, is the techniques used. Addition, subtraction, algebra, integration, differentiation, etc. Physics, to me, is the concepts involved. Problem-solving is not physics. For example, when computing force, math is the multiplication and addition/subtraction necessary to describe the problem, physics is the conceptual basis behind the problem (the various relations between concepts and the concepts themselves that tell you why you're calculating force in the first place), and 'setting up the problem' is essentially bridging the gap between the two. You're translating physics into math.

Just my perspective. Doesn't really matter.

 

[Nikitin]

It's not physics or math that's hard. What's hard is setting up the problem. You can run through disgustingly long and complicated integrals like they were 1+1, and still get knocked on your butt by physics math that is often simple arithmetic.

Physics is not a formula-based activity. You can't memorize your way through physics like you can with chemistry, biology and the like. You have to understand the conceptual difficulties in the problem, then translate that concept into another language: Mathematics.

Maybe biology but sure as heck not chemistry (speaking about 2. grade/12. grade (17 year olds) level)

I definitely agree about your math/physics comment. Physics simply uses math as a language, so usually the math is fairly simple.

At first I had real problems adjusting to "thinking physics", but after a while I am OK with it and getting good grades.

 

[NeedsHelp1212]

well I felt like i did OK. It was not easy but it was not terribly hard. Every multiple choice question was tricky in some way, and there was a couple that i had to guess on (these were not the math ones actually). For example, one of the questions had 3 boxes and said if all boxes were pulled with the same magnitude of force F on which box would the kinetic friction be the greatest? The least? And one of the boxes was being pushed horizontally, another was being pushed with an angle forward. So from those 2 the first one would have more friction b/c the x component on the 2nd one is obviously less. But I am confused with the 3rd box. The force was like coming down from the top left. It made no sense.

Another had a picture of a door and force of the same magnitude applied to different parts of the door. And you had to apply the concept of torque to rank in order from greatest to least in terms of torque. And i knew if its at a 90 degree angle (since u take into account sin 90) it would be at the most. Ohhhhhh wow, nvm... i forgot to take into account distance from the hinge...wow.

So yeah basically there was 25 multiple choice, 3 points each. And then 3 open ended worth a total of 25 points. I think i got all of the open ended right.

 

[Angry Citizen]

For example, one of the questions had 3 boxes and said if all boxes were pulled with the same magnitude of force F on which box would the kinetic friction be the greatest? The least? And one of the boxes was being pushed horizontally, another was being pushed with an angle forward. So from those 2 the first one would have more friction b/c the x component on the 2nd one is obviously less. But I am confused with the 3rd box. The force was like coming down from the top left. It made no sense.

Use your definitions. Kinetic friction is dependent on four things: The mass of the object, the magnitude of local gravity conditions (little g), the coefficient of kinetic friction, and any extra force in the y direction. We know little g is 9.8 meters per second squared (assuming this question wasn't one of those alien planet questions). Do we know the masses of the objects? If not, are they all the same mass? Can we assume that all the coefficients of kinetic friction are the same?

From the problem definition, we know that one of the boxes has extra force in the y direction, while one of the boxes does not. The extra force in the y direction, depending on whether it worked with gravity (pushed down on the box) or against gravity (pulled up on the box), would affect the normal force acting on the box. Use the fact that force is a vector quantity to separate it into its x and y components. For the horizontal force, this is unnecessary because all the force is in the x direction. For the funny one at an angle, you need to separate it into its components using vector algebra.

So, if you have three boxes of equal mass (m1=m2=m3), all of the same material and on the same surface (μk1=μk2=μk3, or in other words all the coefficients of kinetic friction are the same), and they're all in the same gravity field (Earth's), then the only possible difference can come from the direction in which the equal force is applied. Thus, the box with the greatest kinetic friction is going to be the box whose force vector is directed downwards (with gravity, thereby increasing the acceleration, thus increasing the normal force, thus increasing the kinetic friction), and the one with the least kinetic friction is going to be the one whose force vector is directed upward (against gravity, thereby counteracting some of the acceleration, thus reducing the normal force, thus reducing the kinetic friction).

Hope this helps.

Another had a picture of a door and force of the same magnitude applied to different parts of the door. And you had to apply the concept of torque to rank in order from greatest to least in terms of torque. And i knew if its at a 90 degree angle (since u take into account sin 90) it would be at the most. Ohhhhhh wow, nvm... i forgot to take into account distance from the hinge...wow.

Well, think of it this way. Have you ever tried to open a door by pushing near its hinge? Takes a lot more force, huh. Just use that intuition in physics. You've done physics for many years without even realizing it.

 

[NeedsHelp1212]

so the one directed downwards has the most kinetic friction? That's what i put! I kind of figured just using logic if your "pushing" down on something there will be more friction.

For the door one I know exactly what you mean but honestly it was a lot more complex because at one point there was multiple forces acting just at different angles. Well not really complex now but what can you do now

And i screwed up on another problem after someone told me what they did. It's so easy too. They gave you the change in velocity (the car was going West) and the time. So it asked for the acceleration. Obviously just divide the change and without thinking i put 10 m/s^2 West. My friend's right though; since the car slowed down (thats what the problem stated) the acceleration would be in the East direction right? Now i remember that was one of the answer choices. Wow already down to a 94... no way i got an A

 

[Angry Citizen]

That's correct. In order to affect a decreasing change in velocity, the acceleration would have to be in the opposite direction of movement.

 

[Ryker]

Use your definitions. Kinetic friction is dependent on four things: The mass of the object, the magnitude of local gravity conditions (little g), the coefficient of kinetic friction, and any extra force in the y direction. We know little g is 9.8 meters per second squared (assuming this question wasn't one of those alien planet questions). Do we know the masses of the objects? If not, are they all the same mass? Can we assume that all the coefficients of kinetic friction are the same?

From the problem definition, we know that one of the boxes has extra force in the y direction, while one of the boxes does not. The extra force in the y direction, depending on whether it worked with gravity (pushed down on the box) or against gravity (pulled up on the box), would affect the normal force acting on the box. Use the fact that force is a vector quantity to separate it into its x and y components. For the horizontal force, this is unnecessary because all the force is in the x direction. For the funny one at an angle, you need to separate it into its components using vector algebra.

So, if you have three boxes of equal mass (m1=m2=m3), all of the same material and on the same surface (μk1=μk2=μk3, or in other words all the coefficients of kinetic friction are the same), and they're all in the same gravity field (Earth's), then the only possible difference can come from the direction in which the equal force is applied. Thus, the box with the greatest kinetic friction is going to be the box whose force vector is directed downwards (with gravity, thereby increasing the acceleration, thus increasing the normal force, thus increasing the kinetic friction), and the one with the least kinetic friction is going to be the one whose force vector is directed upward (against gravity, thereby counteracting some of the acceleration, thus reducing the normal force, thus reducing the kinetic friction).

Hope this helps.

Hold on, if the force is applied straight downward, then there will be no kinetic friction, since only the normal force will be counteracting the force. You can't have kinetic friction if the force is parallel to the movement (well, there is no movement) and doesn't try and move the box in the direction parallel to the surface.

 

[Angry Citizen]

Hold on, if the force is applied straight downward, then there will be no kinetic friction, since only the normal force will be counteracting the force. You can't have kinetic friction if the force is parallel to the movement (well, there is no movement) and doesn't try and move the box in the direction parallel to the surface.

You're right, of course, but I felt that was pretty obvious given that the problem was about kinetic friction. If the vector is pointed downward while still retaining an x component, and given that the force exceeds the maximum static friction, then my statement remains true.

 

[NeedsHelp1212]

got a 94:) Highest grade in my period :)

 

[Chunkysalsa]

Congratulations, you seem like you've been working hard this year and deserve it.

Do you guys do any E&M stuff, I don't remember doing anything relating to that or optics in High School (but I barely remember high school physics anyway, snoozed to a C).

 

[Brown Arrow]

Step 3 is absolutely terrible. Since when did Physics become an exercise in memorizing formulas?

i agree. i learned it the hard way :/

never sit there and just memorize formulas or constant... when you do question it automatically gets built into your memory... this is how i got to know my stufff in time for exam...

 

[NeedsHelp1212]

Congratulations, you seem like you've been working hard this year and deserve it.

Do you guys do any E&M stuff, I don't remember doing anything relating to that or optics in High School (but I barely remember high school physics anyway, snoozed to a C).

As of this point no, but i remember looking ahead in the book and i definitely saw stuff about optics

 

[NeedsHelp1212]

What is up everyone! I finished with an A+ in the 3rd marking period and just got 1 more marking period to go. But i actually decided to take ap physics next year as a senior. This is crazy, at the beginning of the year I HATED PHYSICS and was horrible at it, but now i actually like physics and am good at it. Thanks for the motivation everyone. Next big decision; what should i major in college. Either something with engineering or business. Big difference but I like both and have taken classes that prepare for both so far in high school (accounting)

 

[Disinterred]

Physics is easy, Math Is Hard.

This is hilarious since any physics problem requires

1) Mathematical Knowledge
2) Physical Intuition

Any math problem requires

1) Mathematical Knowledge

What is harder?

The answer is both can be made incredibly difficult, but physics will always involve that one extra ingredient which can makes problems that much more difficult: physical intuition.

Furthermore, in physics we cannot make up axioms and prove stuff based on them, we are limited by the true test of all truth: experiment. Which also makes physics that much harder.

 

[Shackleford]

Operationally, they are hard because, in many cases, to solve problems, it requires quite a bit of creativity.

My cal 2 professor used the term "mathematical trickery" on more than one occasion when deriving things. I've noticed in CM, QM, and to a lesser extent surprisingly in Thermal, that they pull stuff out of their ***. It is also the same for mathematics.

"Where the heck did that come from?"

I think I like mathematics more because of its axiomatic approach. You use definitions to create more definitions and identify new relationships, etc.

 

[Chunkysalsa]

This is hilarious since any physics problem requires

1) Mathematical Knowledge
2) Physical Intuition

Any math problem requires

1) Mathematical Knowledge

What is harder?

The answer is both can be made incredibly difficult, but physics will always involve that one extra ingredient which can makes problems that much more difficult: physical intuition.

Furthermore, in physics we cannot make up axioms and prove stuff based on them, we are limited by the true test of all truth: experiment. Which also makes physics that much harder.

Is there no such that as Mathematical Intuition. I'm pretty sure it took a lot of creativity and intuition to devise all of this knowledge you call upon to do your physics.

 

[lisab]

What is up everyone! I finished with an A+ in the 3rd marking period and just got 1 more marking period to go. But i actually decided to take ap physics next year as a senior. This is crazy, at the beginning of the year I HATED PHYSICS and was horrible at it, but now i actually like physics and am good at it. Thanks for the motivation everyone. Next big decision; what should i major in college. Either something with engineering or business. Big difference but I like both and have taken classes that prepare for both so far in high school (accounting)

Wow, excellent job, congrats!

You can always double major - not a bad combination, those two.

Keep in mind, having an engineering degree doesn't prevent you from going into business, but having just a business degree pretty much excludes you from getting an engineering job.

 

[flyingpig]

As Walter Lewin would say "you must have had a bad teacher"

 

[NeedsHelp1212]

last day of school today!

I'm not sure what my final grade is until report cards are mailed out but I am hoping i somehow got to an A+ for the year. The final exam was surprisingly easy and i feel i aced it.

The bad news is AP physics will most likely not be available in my school next year. Under 10 people elected to take the class so there most likely not going to offer it. This really sucks since I wanted to challenge myself further. Instead I am going to take AP Bio, since i want an AP science for colleges to see (and i just hate chemistry even though i get good grades in that class).

So yeah, thanks for the advice guys. It's weird looking back at this thread and seeing what people wrote back in October when i felt so horrible about my grades and where i am now. Hopefully, somehow they offer ap physics next year.

**Btw fylingpig: My teacher is not in any way bad, on the other hand I feel he is one of the best teachers I have ever had. He teaches the material clearly and will always be available for help.