Recent content by diegocas

Homework Statement A box is placed on an inclined plane of angle \theta. There is no fiction between the box and the plane nor between the inclined plane and the floor. The mass of the box is m_1 and the mass of the inclined plane is m_2 . Find the acceleration of the box and that of...

Thanks, it is much clearer now. And sorry for my spelling! "hindges" looked odd to me, but I didn't know why.

Apply L'Hopital's rule in the limit \lim x.a^x after writing x.a^x = \frac{x}{a^{-x}} .

Homework Statement A door of mass M , height h and width b is held by two hindges a distance d from the lower and upper edges of the door. What is the force on the hindges? Homework Equations The Attempt at a Solution We may assume the weight of the door ( M\vec{g} )...

In set theory, for example in Zermelo-Fraenkel set theory, you don't define the notions of "set" and "belongs to", you just assume that those notions exist and satisfy some properties (axioms). From that you work on formally. It is clearly stated what notions are defined and what primitive...

Thanks for all the replies to my post! There are quite interesting views about the subject. I'm learning a lot about how physics (the science) works. However, as a mathematician, I should say that I'm a little impressed at how loosely defined certain physical notions are, namely, mass. (Please...

I wonder: What is the fundamental evidence for F = ma? I know, of course, that almost every experiment confirms this equation. However, does that make it true or do we just accept it because it works, it is very simple and it explains lots and lots of phenomena? I think the simplicity issue...

Again, I think that, in the end, it really is about simplicity. We like simplicty and we accept that the simplest explanation is the correct one (Ockham's razor principle). Putting the Sun in the center together with Newton's equations of motion and Universal Law of Gravitation makes a nice and...

I always hear people saying "Ptolemy thought that the Sun moved around the Earth, but it is the other way around: the Earth moves around the Sun". I think that's wrong. I think that Copernicus's theory is not "truer" than Ptolemy's. It is just that Copernicus's theory is simpler! But both...

At the end of this class http://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/embed21/, Prof. Walter Lewin spins a plastic object on the table. The object starts spinning, it stops and immediately starts spinning in the opposite direction. The question...

Thank you very much for both your replies! It's all clear now!

Yes, I know that the rolling ball has not only translational kinetic energy but also rotational kinetic energy. The part that puzzles me about the rolling ball is the following: on the one hand, friction may be ignored and it is the additional rotational kinetic energy that accounts for the...

Thank you! But I have one more question about it. In my calculation, I assumed the ball was rolling, not sliding. Why can we make that assumption? That is only possible because of the friction, isn't it? I did the following: Assume the ball is in a position where the angle from the vertical...

Homework Statement At the end of the lecture in http://ocw.mit.edu/OcwWeb/Physics/8-01Physics-IFall1999/VideoLectures/detail/embed13.htm , Prof. Walter Lewin compares the motion of a slider on a circular air track (no friction) with the motion of a ball on a circular path (with friction)...

Hi! I'm a mathematician but I'm now stuyding some physics. I like it, but I am not completely satisfied with the presentation in ordinary books. I want to find a physics book with no fear for math! In traditional textbooks, line integrals, surface integrals, Stoke's theorem is always avoided! I...