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  1. kjohnson

    Hardest ME undergrad course?

    I think the most difficult course mathematically is easily fluid mechanics. It was the first course outside of the math department that relied pretty heavily on differential equations (including partial).
  2. kjohnson

    Integration - Finding Areas

    Also another tip...you don't need to worry about splitting the interval up according to the roots, the sign of f(x) will take care of everything. There is nothing wrong with splitting the integral up, but it is not necessary for most simple continuous functions.
  3. kjohnson

    Integration - Finding Areas

    That is a good question...from a purely geometric standpoint then yes. But mathematically the area below the x-axis is taken to be negative because the differential area is defined as: dA=f(x)dx and when f(x) is negative then that value of dA will also be negative since dx is positive...
  4. kjohnson

    Integration - Finding Areas

    I believe your problem is in the absolute value? The area that is below the x-axis should be counted as negative.
  5. kjohnson

    Numerical differentiation of a dataset

    You could try passing some sort of "best fit" function through the data and then simply differentiating that function.
  6. kjohnson

    Structural Analysis- small deformation

    Re: Structural Analysis-"small deformation" 1. Yes you can use finite element method to model the problem. 2. Linear elasticity problems can involve large deformation, as long as the stresses and strains within the material do not exceed the linear region. For example a very thin beam...
  7. kjohnson

    Radial solutions to laplace equation

    After doing some thinking I don't know if 'u' can be linear in theta (at least physically). Because if it was linear in theta then at theta=0 'u' would have some value, while at theta=2pi 'u' would have some different value despite the fact that theta=0 and theta=2pi correspond to the same...
  8. kjohnson

    Radial solutions to laplace equation

    Yes, when its linear in theta. How do you know when its linear in theta...thats a good question. I will have to do a little thinking on that one, this stuff is kinda new to me as well ;). Hopefully that gives you at least some idea and if I come up with something I will keep you updated.
  9. kjohnson

    Radial solutions to laplace equation

    Yes if u(r) only then it would surely drop out. But that is not the only way... For a moment ignore the partial and just think of it like a normal derivative, more specifically notice it is a second derivative. When would the second derivative of some function equal zero?
  10. kjohnson

    Radial solutions to laplace equation

    Look at \frac{\partial^2u} {\partial\theta^2} When would this term vanish from the equation...
  11. kjohnson

    Why am I struggling with Differential Equations?

    Re: Why am I struggling with Differential Equations?? Differential equations isn't necessarily a "cookbook" class, it just depends on how its studied/who is teaching it. Yes, in many undergrad engineering classes it is taught in a cookbook style, but just because you know a few tools to solve...
  12. kjohnson

    Studying Dose Mathematicians understand their books?

    Haha, yeah it is a discussion that could go on forever. I'm not trying to start it, just trying to point out that it is headed that direction.
  13. kjohnson

    Should machines replace human workers?

    My thoughts exactly. Look, you can only replace a persons job if it is something repetitive that can be coded and run by a machine (like a factory). Notice you still need people there to monitor the process in case something unexpected happens. Basically this is just society evolving to fit...
  14. kjohnson

    Studying Dose Mathematicians understand their books?

    This is an interesting conversation that seems to touch on the philosophy of: Is mathematics a tool created used to describe the universe? or Is mathematics the "language" of the universe (i.e. it would exist even without the humans who use it)? This is probably better off for another...
  15. kjohnson

    Acceleration of 2 boxes sliding down ramp - need help please!

    Its just the sum of the friction forces for both blocks. I was not 100% sure how the system approach would work but it seems that if you do it as a system it is the same as if you wrote an equation for each block and added them together canceling out the interaction force 'F' between them.
  16. kjohnson

    Acceleration of 2 boxes sliding down ramp - need help please!

    By the way you can solve for the acceleration of the blocks by solving it as a system vs writing equations for each block. But then you will still have to write and equation for one of the blocks to find the force 'F' that acts between them...
  17. kjohnson

    Acceleration of 2 boxes sliding down ramp - need help please!

    Draw them out as separate and draw Free body diagrams then equations for each block. Your table looks ok for the entire system but you should label 'Fgravity' as 'Fparallel' or something like that indicating that it acts parallel to the ramp. The value of 'Fgravity' is just 'mg' and it acts...
  18. kjohnson

    Acceleration of 2 boxes sliding down ramp - need help please!

    Yep. This is the case for tackling almost any problem. So what do you get?
  19. kjohnson

    Acceleration of 2 boxes sliding down ramp - need help please!

    You need to write your equations of motion for each box. After doing this what do you have in the inclined direction? Remember Newton's third law...
  20. kjohnson

    Notes on integration

    Looks great! If you don't mind me asking, what programs did you use to make this...(i.e. for getting a nice math font, pictures, etc).
  21. kjohnson

    Friction: what is the net force on the block the instant that it starts to slide

    If its moving you always use kinetic friction. Even if its barely sliding at constant velocity.
  22. kjohnson

    Load Distribution/Rigid Body Equilibirum Problems

    I think you may need to check your moment summation again, but i could be wrong (i just glanced at the problem quick)... Anyway it seems like you are more stumped on the concept. What you are doing is taking a system (bar in this case) that is being loaded in two ways: 1. applied forces-...
  23. kjohnson

    Work in 3D

    Yes, work is equal to Fx*dx+Fy*dy+Fz*dz where where Fx,Fy,Fz are the force components and dx,dy,dz are the displacement components...but there is another common way to write the the dot product of two vectors that should make quick work of this problem.
  24. kjohnson

    What do orbitals look like?

    haha this cracked me up
  25. kjohnson

    Traction Around a Cylinder

    I believe what you are looking for is called belt friction. Here is the wiki link that has the basic formula: http://en.wikipedia.org/wiki/Belt_friction There are some other sites & videos you could find if you want a full derivation.
  26. kjohnson

    Ways to teach yourself physics?

    I believe this is a very important point that can't be stressed enough. You can read the books and do problems and have a good idea what is going on. But chances are you will have (& should have) questions that arise when learning something new. Even if it seems like a small step and you are...
  27. kjohnson

    Getting An Engineering Internship

    I think a good way to go about it would be as follows: 1. Try your best to get an idea what rough area of aerospace you want to pursue further work in (though early in your studies it may be just a guess). 2. Figure out what professors work is best inline with your goals. 3. Email the...
  28. kjohnson

    Does it take time to get used to physics?

    Re: Does it take time to "get used" to physics? I would have to agree with a lot of this. I would also like to add a few things I've personally noticed when studying physics/engineering: First is that it always seems like I'm a couple years behind on actual understanding. Its not that I...
  29. kjohnson

    Dealing with inexperienced/overambitious members

    I agree. This is all I'm trying to say. Everyone will have their opinions and lean one way or another, but trying to be informative while still giving some positive feedback is like walking a tight rope. Its simply a balancing act and I think everyone would benefit (me included) from taking a...
  30. kjohnson

    Dealing with inexperienced/overambitious members

    Yes this is true. I like to think of this popular science as kind of a hook. Its easy to get people interested and excited about it. Then as they begin their journey into learning actual basic physics and so on they will hopefully apply that natural curiosity to more realistic problems. Of...
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