# Recent content by electricsheep

1. ### MATLAB Using an ADSR Envelope in MATLAB

Whenever you suspect a dimension mismatch issue, you can always inspect the dimensions of the matrices in question in the workspace window, or using the size function. That should narrow the problem down to a specific matrix.
2. ### Ethernet, Profinet and Profibus

Heh, thanks Carl and berkeman. After more hours of research and learning about some basics, here's my refined version that I will present to my lab demonstrators tomorrow, if they ask for it. I've tried to focus on comparing and contrasting the three rather than talking them in general...
3. ### Ethernet, Profinet and Profibus

Hi. Firstly I realise this may be classified as a homework question, so please move it if necessary. Problem For a lab using PLCs, I'm supposed to answer this question: What is the difference between Ethernet, Profibus and Profinet? My attempt This is for a control subject, but due to...
4. ### Infinite speed

Nice. That wasn't what I was trying to point out. Your original expression for relativistic momentum had v^2, which made me do a double take and do a quick search on the web just to confirm my memory. But yes, I think I'm thread-jacking now. My apologies.
5. ### Infinite speed

Actually, I don't think E is the rest energy, because that would imply m is the rest mass, which is not incorrect but entirely irrelevant to what I was explaining there. I'm fairly sure E is properly defined as the "mass energy", which is just the amount of energy equivalent to a certain mass...
6. ### What happens when you point a laser-pointer into the sky?

I would agree with the others and say that once out of the atmosphere, your photons will keep going until intercepted by matter. However, the atmosphere is pretty thick, so there would be quite a bit of scattering and whatnot for a little laser pointer.
7. ### Infinite speed

Hi DaveC, I may be nitpicking here, but when I studied special relativity back in high school, I had a lot of trouble with statements such as this one, because it doesn't specify the frame of reference from which you're viewing the body. I feel it's important to specify that here, "constant...
8. ### Halliday/Resnick/Walker - Text Question

I was supposed to use HRW as a prescribed first year physics textbook. It's decent, but it's really a matter of personal preferences. I ended up using "Understanding Physics" by Cummings et al, which is *very* similar in style to HRW and a bit cheaper. :blushing: For a bit of further...
9. ### Simple question on polynomials

OK, first are you happy with this one: we have f(x) = x^2 - 4x, what is f(a)? (Answer: f(a) = a^2 - 4a. i.e. you just plug a into wherever x used to appear. It does NOT mean "f(a) = f(x) * a", which is similar to what you seem to have done in your attempt.) Now, use the same technique for...
10. ### Water and High-Speed Impact

Wasn't this done on Mythbusters? If I remember correctly, they found that breaking the surface tension with a hammer didn't really help when the dummy was thrown from a sufficient height. (By the way Panda, what does "IRC" stand for in the context of your post? :blushing: )
11. ### Infinite speed

To expand on AlephZero's mention of Einsteinian physics: The faster something moves, the more kinetic energy it has. E=mc^2, so the faster it moves, the heavier it becomes. The heavier it becomes, the greater force is required to accelerate it more. If that is possible, then it becomes...
12. ### Zener Diode: germanium vs. silicon

This is a strange one, and I'm afraid I cannot help much. However, are you sure you're supposed to determine whether a *zener* diode is made of silicon or germanium? (If it's just a diode, we can inspect the forward threshold voltage, but I'm not sure about zener diodes. Could it be a...
13. ### Transformer vs ohm's law

Yep. Remember that Ohm's law only applies for Ohmic devices (which obey Ohm's law and hence named thus). (Seriously, I'm not trying to be smart or patronising here.)
14. ### Convert 120Watts to 15000Watts

Hear, hear. Perhaps this explanation helps: power is the time rate of change of energy. Your power supplies are only capable of each providing a maximum of 60 J of energy per second, and you want 15000 J per second out. Conservation of energy (ie. you can't get out more than what you put in)...