# Search results

1. ### Does anyone know what this equipment is for?

Hello, I have found this chemistry equipment, but I cannot determine what it is for. I have a suspicion it is for measuring boiling point temperature elevation. I have included a drawing of how I think it should go together. It consists of a conical flask connected to a graduated boiling tube...
2. ### Equation from neuroscience textbook, regarding modeling neurons

Hello, I am trying to understand an equation from the textbook "Theory of neural information processing systems" by Coolen, Sullich and Kuhn. The book states that "the evolution in time of the postsynpatic potential V(t) can be written as a linear differential equation of the form: \frac...
3. ### Applied maths, monotonic function

Regarding x=0: Thanks qwerty, I didn't notice that; I need to be more careful. Regarding differentiability: Thanks for the information; I'll need to go and look into that a bit more as I am not that familiar with it (I vaguely remember something about it...!).
4. ### Applied maths, monotonic function

Thanks for the response, RUber. I never thought of doing that; I guess if you know that the function is monotonic, then that would be a quick way of identifying whether it is increasing or decreasing. I wanted to identify if it was also monotonic. It is reassuring that both methods agree that it...
5. ### Applied maths, monotonic function

Hello, The equation is from a chemistry calculation; the textbook claims that the function is monotonic, without specifying whether it is monotonically increasing or decreasing. Depending on the starting conditions, the function can look different; I basically want to know if the following is...
6. ### PH meter design

Thanks for the reply Borek. I assumed this might be the case. This relates to the point I made earlier regarding the theoretical "infinite resistance" of a voltmeter: in that case, there wouldn't be any change, but an "attempt" to change is present. In reality, something is changing at the...
7. ### PH meter design

Thanks for the response Borek. I found some useful sources which I will try to add when I can access a computer. Doing it on a tablet is difficult. Just briefly, let's say hydrogen ions, or as some sources suggest, sodium ions cross the glass bulb (if, incidentally, hydrogen ions do cross the...
8. ### PH meter design

Hi Borek, Apologies if the post was long, but I believe there is a lot happening in a pH meter. Basically, I want to know how a pH meter works. I can't find an online source that goes step by step, without making assumptions about the readers knowledge or omitting important information. I...
9. ### PH meter design

Hello! I have a question concerning the functioning of a pH meter. All the sources online that I can find either omit, I think, important information, or describe it in "technical terms" with equations. I would like to know what is happening at the level of the distribution and movement of...
10. ### Velocity is proportional to distance

Don't worry: If the distance doubles as time doubles then the acceleration would have to be zero, since the average velocities would have to be the same. But the problem involves non-zero velocity, and so the distance does not double as the time doubles. Kind of obvious and I completely missed...
11. ### Velocity is proportional to distance

Thanks for the replies. I am not sure if it is an error in the book, but perhaps the acceleration is not constant and the relationship is simply |v| = kx and I do not need anything more "fancy" to solve the problem (such as differential equations), I might be neglecting something obvious. The...
12. ### Velocity is proportional to distance

Hi Orodurin, thanks for the reply. The chapter concerns kinematics with either zero or constant acceleration. It doesn't even assume much familiarity with calculus so I can't see that the question would require one to solve a differential equation. That's why I thought acceleration would have to...
13. ### Velocity is proportional to distance

Homework Statement An object starts from rest at the origin and moves in the positive x direction. The velocity is proportional to the displacment. I am trying to find the equation linking velocity to displacement. Homework Equations Since the object starts at rest and then moves in the...
14. ### Average speed question: forwards then backwards

Thanks for the reply. I guess it's just an error in the textbook.
15. ### Average speed question: forwards then backwards

In the textbook the value from A to B is 8.8 m/s and from B to A it is 6.6 m/s. They give the answer as something like 2.6 m/s. I got 7.54 (to 2 d.p.): 40 m / [(20/8.8) + (20/6.6)] s = 7.542857143 m/s.
16. ### Average speed question: forwards then backwards

Homework Statement An object starts at the origin, position A; then travels 20 m to position B; then returns to position A. From A to B the average speed is 10 m/s; on its way back the average speed is 6 m/s. What is the average speed for the entire trip? Homework Equations average speed =...
17. ### Steampunk-esque novels

Yeah Mieville seems to be a blend of different genres. At least that is what I got from Perdido street station. I really enjoyed some of the ideas and characters, especially the Weaver, which I think he done really well. I was planning to read Railsea but apparently it riffs off of Moby Dick and...
18. ### Steampunk-esque novels

Hello! I have started to take an interest in steampunk and related genres. I read China Mieville's Perdido Street Station and enjoyed his writing style and some of the ideas and imaginative characters. However, it wasn't "pure" steampunk. I tried The difference Engine but it didn't provide...
19. ### Pycnometer equation

Thanks for the responses. I have a really dumb question: if something is flat on the surface, how can the air "push up" underneath the bottle? Dumb question, I know, but I am trying to visualise where the pressure comes from! Thanks for the responses so far!
20. ### Pycnometer equation

hello! On wiki, regarding specific gravity, it gives the derivation for the pycnometer equation for determining specific gravity. However, the first equation confuses me. It goes as follows: The pycnometer, placed on a balance, will exert a force: F = g(m_b - \frac{ \rho_a m_b}{ \rho_b}) The...
21. ### PHP HTML and PHP issue: display HTML form variables using PHP echo

Thanks voko, I have decided to get a different PHP book; a more recent one.
22. ### PHP HTML and PHP issue: display HTML form variables using PHP echo

Thanks for the link Adyssa; as you say, they use \$_POST, the book has so far made no mention of it (I found it on a web forum). Looking back through the book, it does say 'send data'; it also used the words 'field' and 'variables' but without actually explaining in any way what is happening...
23. ### PHP HTML and PHP issue: display HTML form variables using PHP echo

Heeeeeeellllllllllllllooooooooooooo, I have a question about HTML and PHP: Firstly, I am using Apache2 and PHP5 (I think) and running it as a localhost. I created a simple HTML form that sends the variables via post to a PHP file; there are two variables with the names "nickname" and...
24. ### C: malloc() doesn't just allocate memory

I should have tried this earlier; I didn't have the confidence because I wouldn't be happy that what I did was a correct method to test anything! I decided to assign the address returned from malloc() to a char * pointer and then assign the address from the char * pointer to the struct pointer...
25. ### C: malloc() doesn't just allocate memory

Is it in any way accurate to understand this to mean something like the following: I have my structure happy as before. I declare a pointer that points to a structure of type happy. struct happy *h_ptr = NULL; When I assign space in memory using malloc() it would simply set aside that space...
26. ### C: malloc() doesn't just allocate memory

Hello, Another (probably obvious) question: malloc() assigns memory space in bytes; e.g. malloc(100) assigns 100 bytes of space and returns a pointer. However, in creating a linked list, I can allocate space a assign it to a pointer and the structure already exists? For example...
27. ### C programming: pointer assignment only in main()?

Many thanks for the responses!
28. ### C programming: pointer assignment only in main()?

Thanks for the feedback everyone. This is the part that still confuses me, sorry if the answer is in one of the responses, I can't seem to put the pieces together: Why does the following not follow the same pattern: char *mssg; mssg = "Hello"; ... int main( void ){ ... return 0;} The mssg...
29. ### C programming: array declared before main() and initialised in main()

Thanks for the links Integrand; I'll finish this textbook on C because I am half-way through and I have put in the effort already! I bought another textbook on C++ to start afterwards, one good thing is that C has eased me into this type-of programming.
30. ### C programming: array declared before main() and initialised in main()

Thanks for the responses everyone! I was planning on familiarising myself with C then moving onto C++ - the textbook assures me this is a good move.....