# Search results

1. ### I Partitioning a whole number in a particular way

Another example is: w1 = 11 w2 = 39 w3 = 3 W = 53 P = 25 ROUND(P*w1/W) = 5 ROUND(P*w2/W) = 18 ROUND(P*w3/W) = 1 This sums to 24 but we have 25 pieces.
2. ### I Partitioning a whole number in a particular way

I'm not sure what round off means. If round off means raise anything with a decimal >= .5 the next whole number and anything with a decimal <.5 to the next whole number down, then the example will still lead to 18 pieces being assigned.
3. ### I Partitioning a whole number in a particular way

Thanks for the replies. I don't mind so much favoring someone more than others as long as: (ai<=wi) is not violated we assign exactly P pieces of pizza. no more, no less only whole slices can be assigned (no fractions for ai) For example, if we have w1 = 25 w2 = 9 W = 34 P = 17 Then...
4. ### I Partitioning a whole number in a particular way

Hi, Let W be the sum of all the people's weights, let P be the total number of pizza slices available. If: I have P slices of pizza (P<=W) I have n people I want to split the pizza with I want to use people's weight to determine how many slices they get (more weight -> more slices) I don't...
5. ### I Physics of a bell siphon

In the past i've made these bell siphons following these instructions: http://www.affnanaquaponics.com/2010/02/affnans-valve-detailed-explanations-of_9459.html I've had good success but that was just blindly following instructions and now I am just very interested in knowing the effects of...
6. ### I Physics of a bell siphon

It's definitely growing in popularity! I think it's fun because you get to combine 3 hobbies: raising fish, growing plants, and building hydraulic systems (siphons, pumps, waterfalls, filtration, etc.) Apparently the physics of a bell siphon are pretty complicated, but do you think you can help...

Thanks!
8. ### I Physics of a bell siphon

I'm trying to build a home aquaponics system, and a key component of the design I got off the internet is a bell siphon. So I'm trying to understand the physics of this siphon effect so I can optimize the weight and dimensions of the siphon to fit the size of my system. From what I read on the...
9. ### Measuring torque acting on motor shaft?

I have an electric motor that I am using to turn an auger to dispense pet food. I want to measure the average torque required to turn this auger at a given rpm. I know Powerin = Voltage into motor * Current into motor and Powerout = Torque exerted by shaft * RPM of auger and Powerout...

bump ^
11. ### Piezoelectric Crystal Shoes?

It takes 120 J of energy to light two 60-watt light bulbs for 1 second, right? And the average phone takes 18000 Joules of energy to completely charge so that's only 150 steps! ... I'm sure there is something wrong with that line of thought, haha
12. ### Piezoelectric Crystal Shoes?

I was inspired by this article http://science.howstuffworks.com/environmental/green-science/house-music-energy-crisis1.htm to wonder if one could put piezoelectric crystals in the sole of a shoe and perhaps harness the energy to charge their iPod? Can someone let me know if this is feasible...
13. ### Calculate attractive force between Cu2+ and O2- ions.

The equation F= ke(|q1q2|)/r2 looks good. So if I plug in 3.204 × 10^-19 coulombs for q1 and -3.204 × 10^-19 coulombs for q2 (because O2- has a net charge equal to -2 times the charge of an electron and Cu2+ has a net charge equal to twice the charge of an electron), then I get 2.307*10-8...
14. ### Calculate attractive force between Cu2+ and O2- ions.

Well I don't know the force equation, my teacher only gave us the equation for bonding energy... Perhaps since energy=force*distance we can find force by dividing our energy equation by some distance? I'm still stuck but I see now that z_1= 2 and z_2=-2. Any more help?
15. ### Calculate attractive force between Cu2+ and O2- ions.

Homework Statement Calculate the attractive force between a pair of Cu2+ and O2- ions in the ceramic CuO that has an interatomic separation of 200pm. Homework Equations E_A= -\frac{(z_1\cdot e)(z_2\cdot e)}{4\pi\cdot\epsilon_o\cdot r} Where z_1 and z_2 are the valences of the two ion...
16. ### Finding number of atoms per cm^3 of zinc?

Homework Statement Zinc has a density of 7.17 Mg/m^3. Calculate (a) the number of Zn atoms per cm^3, (b) the mass of a single Zn atom and (c) the atomic volume of Zn. Homework Equations atomic mass of zinc = 65.39 g/mol The Attempt at a Solution For part (a) I use the fact that...
17. ### Finding the energy of an electron from n=4 to n=2?

Homework Statement Find the energy of a He+ electron going form the n=4 state to the n=2 state. Homework Equations E_n=\frac{m\cdot e^4 \cdot z^2}{2n^2 \cdot \hbar^2} Where m= mass of electron, z= atomic number, e= charge of an electron, n is the energy level. ^ I think those are...
18. ### Computing energy in the electron of Li 2+?

Homework Statement Using the Bohr model of the atom, compute the energy in eV of the one electron in Li2+. Homework Equations E_n=\frac{m\cdot e^4 \cdot z^2}{2n^2 \cdot \hbar^2} Where m= mass of electron, z= atomic number, e= charge of an electron, n is the energy level. ^ I think...
19. ### Period of an Oscillating Particle

Sorry, how do we have ## \frac {dt} {dx} = f(x) ##?
20. ### Period of an Oscillating Particle

"Period" is the time it takes for the particle to make one cycle. The particle traveling from 0 to A takes 1/4 of the time it would take to travel the whole period. But I don't see how we can find the time it takes the particle to travel from 0 to A? We have this equation that gives us time...
21. ### Period of an Oscillating Particle

If ##\frac{dx}{dt}=a+x## then ##\frac{1}{a+x}dx=dt## (whatever that means), so ##\int \frac{1}{a+x} dx = \int dt = t##. So ##ln(a+x)=t##. If ##\frac{dx}{dt}=x^2## then ##\frac{1}{x^2}dx=dt## (once again idk what exactly i'm doing there), so ##\int \frac{1}{x^2}dx = \int dt##. So...
22. ### Period of an Oscillating Particle

I'm afraid I don't get what it means to take ##\frac{dx}{dt}=f(x)## and turn it into ##\frac{1}{f(x)}dx=dt. And thus I don't get what it means to then take the integral of both sides of that... can you help me make sense of what those procedures mean?
23. ### Period of an Oscillating Particle

oh whoops the integral of velocity is displacement so we would have x(t). So we could solve x(?)=A and then multiply it by 4 to get the period?
24. ### Period of an Oscillating Particle

##\frac{dx}{dt}=f(x)## ##\frac{1}{f(x)}dx=dt## ##\int f(x)^{-1} dx = \int 1 dt=t## is that right? That would give us time as a function of velocity which can give us velocity as a function of time? Then we can integrate that with respect to t to find displacement as a function of time...
25. ### Period of an Oscillating Particle

Since the input into our velocity equation we found is x not t, I should edit: ... to say: See how as we make Δt smaller and smaller, the above becomes a better and better approximation of displacement x as a function of time? But I don't know how to turn that method into an integral...
26. ### Period of an Oscillating Particle

Homework Statement A particle oscillates with amplitude A in a one-dimensional potential that is symmetric about x=0. Meaning U(x)=U(-x) First find velocity at displacement x in terms of U(A), U(x), and m. Then show that the period is given by ##4\sqrt{\frac{m}{2U(A)}}\int_0^A...
27. ### Help Understanding Quotient Groups? (Dummit and Foote)

I don't understand, why can't we just say: If ##aK=a'K## and ##bK=b'K##, then ##(aK)(bK)=(a'K)(bK)=(a'K)(b'K)##. ?
28. ### Help Understanding Quotient Groups? (Dummit and Foote)

I don't see why K needs to be normal? In order for ##(G/K,\cdot)## to be a group we need: i) ##g_1K\cdot(g_2K\cdot{g_3K})=(g_1K\cdot{g_2K})\cdot{g_3K}##. ii) ##\exists{e\in{\frac{G}{K}}}## s.t. for all g in ##\frac{G}{K}##, ##e\cdot{gK}=gK##. iii) for every ##gK\in{\frac{G}{K}}## we need...
29. ### Help Understanding Quotient Groups? (Dummit and Foote)

I left out one part of the definition. It should say "Let ϕ:G→H be a homomorphism with kernel K. The quotient group G/K is the group whose elements are the fibers of ϕ (sets of elements projecting to single elements of H) with group operation defined above: namely if X is the fiber above a...
30. ### Help Understanding Quotient Groups? (Dummit and Foote)

The definition given is... "Let ##\phi: G \rightarrow H## be a homomorphism with kernel ##K##. The quotient group ##G/K## is the group whose elements are the fibers (sets of elements projecting to single elements of H) with group operation defined above: namely if ##X## is the fiber above...