Fun Physics Problem

Given this experimental setup and ignoring friction: What is the acceleration of m₁ and m₂ (they're the same, of course)? Answer at How to Solve a Physics Problem Undergrads Usually Get Wrong (I think he makes the explanation overly complicated), but give it a whirl first.--Percy

a = f/m.
The force is the force of gravity on M2.
The mass is M1 + M2.That seems to easy so it must be wrong.

It's a problem that most *undergrads* get wrong, not us! And even those of us who are undergrads probably still get it right. --Percy

Would it just be the acceleration of gravity?Not an undergrad, but I only took one physics course and that was over eight years ago. ABE: Just looked at the answer and I can't tell if I'm right or wrong. Edited by Jon, : No reason given.

The usual mistake is to forget that the force has to accelerate m2 as well as m1, to think of m2 as providing the motive force by virtue of its weight, and m1 as being the thing to be moved. I've seen really bright people struggle with this (specifically my elder and younger brother, both now Ph.D.s in assorted scientific fields).

The final formula says I am right, but the explanation is so complex I don't know why he does all that to get there.To me it is simple:
The only unbalanced force is that of gravity on M2 and the only mass to be moved is the two of them together. Why all the rest?

Of course your method works.Physics students are taught to look at the problem in a slightly more complex way, namely analyzing the forces on m1 and on m2 separately and then applying the constraint from the string that the acceleration on the two masses is the same. This more general method works even when we do things like add friction to the horizontal surface, consider the mechanical energy stored in the pulley, or when we change the string to a spring. In those case, the simplified method becomes more difficult and maybe even impossible to apply.Almost certainly the video used an unnecessarily general method to solve this simple problem. I did not look at the video to confirm that.

Because he has an article to write.

quote:

---

If I just solved the problem the correct way, it wouldn’t be that much fun. Instead, I am going to set up an experiment to show that the tension in the string isn’t just the weight of mass 2.

---

The last section title 'Solution to the Half-Atwood Machine' is the boring 'to the point' solution, with working.Edited by Modulous, : No reason given.

Pfft. I took three physics classes and passed two of them but that was thirty-five years ago.Which is probably why I don't understand the question.My answer is six.