# Search results

1. ### Spin-up effect?

Hi. Can anyone explain to me what spin-up effects are? The context is a waterwheel that consists of an ordinary wheel with papercups with holes in the bottom suspended along the rim. It is stated that for this wheel there are two sources of damping: ordinary frictional damping and "inertial"...
2. ### Meaning of formula from statistical physics

Ok, thanks guys!
3. ### Meaning of formula from statistical physics

Hi. Can anyone explain the meaning of this formula from statistical physics to me: S = -k\sum_r{p_r\ln p_r} Ok, I know that S is the entropy, the p's are probabilities of some sort - but somehow this is not satisfactory :-)
4. ### Very Very Basic Question

According to Ohm's law voltage and current are proportional for a given resistance: U = RI If you increase U, I increases correspondingly. When people say that "high voltage means low current" it is probably because they are interested in the power output: P = UI If you...
5. ### Einstein and the photoelectric effect

Most physics books says something like this on the photoelectric effect: "the photoelectric effect provided strong evidence of the particle nature of light - and it eventually led Einstein to propose that light consisted of discrete packets of energy (photons) in 1905." I have been told...
6. ### Polarization of electromagnetic waves

I have read some stuff on the internet and I have come to this conclusion: "an electromagnetic wave is linearly polarized if the E-field is - at all times - aligned along some fixed axis.. an unpolarized wave is a wave in which the E-field is randomly oriented (that is, it has different...
7. ### Polarization of electromagnetic waves

but isn't a superposition of polarized waves itself polarized (with respect to some superposed direction)??... what exactly is polarized light as oposed to unpolarized light??
8. ### Polarization of electromagnetic waves

I have read briefly about polarization of electromagnetic waves and from what I understand an electromagnetic wave is said to be polarized in some direction if the E-field is aligned along this direction.. what then is unpolarized light?? - the E-field has a definite direction at every point...
9. ### Frequencies and overtones

by "the strings frequency" i mean the frequency with which the particles of the string vibrates, which must be the same for all particles if the wave is sinusoidal.. or am I missing something?? if you for example pluck a guitar string at some point, then the resultant vibration can be...
10. ### Frequencies and overtones

thanks again.. it's just the phrase "several frequencies at the same time", which to me seems analagous to e.g. a particle being at several positions at the same time or having several different velocities.. isn't it more accurate to say something like "the strings vibration is a sum...
11. ### Frequencies and overtones

thanks for answering. so "several frequencies" simply means that the there is no unique frequency because the wave pattern is constantly changing, which in turn is because there can't be a perfect standing wave because of the physical properties of the string (the length) or...?
12. ### Superposition of sound waves

thanks for answering, but I still don't understand how we are able to sort out the individual wave-components in a composite wave.. i'm not really sure if I understand integral's comment, but what I get from it is that there is only one possible combination of individual wave components that...
13. ### Frequencies and overtones

it is often said that the rich sounds produced by e.g. a guitar is due to the string vibrating at several different frequencies at once.. does this mean that there is both the fundamental frequency and several overtones present at the same time.. if so, I don't get it.. how can there be more...
14. ### Superposition of sound waves

how are we able to clearly distinguish two different sound waves - like when someone is talking to us while music is playing in the background... i've read it is due to the superposition principle which states that the waves combine and form a resultant wave that is the sum of the individual...
15. ### Simple question (electricity)

Thank you.. so the presence of the new resistor somehow alters the electric field, so that the dissipated energy in the first resistor drops to the value corresponding to 1/2*emf??
16. ### Simple question (electricity)

I have a somewhat simple question, that I for some reason can't figure out.. suppose you have a circuit with a source of emf (e.g. a battery).. if you put a single resistor in this circuit there is a potential drop equal in size to the emf (i neglect internal resistance in the source).. now...
17. ### Bernoulli's equation and conservation of energy

Why is it that you only account for the kinetic and potential energy change in the blue volumes.. What about the fluid between them?
18. ### Bernoulli's equation and conservation of energy

Can anyone explain to me how Bernoulli's equation arises from conservation of energy?
19. ### Mechanical equilibrium

my physics book implicitly states that if an object is rotating it is not in mechanical equlibrium - even though there is no net torque and it isn't moving through space (no net force)... but if the same object is moving through space with constant velocity (no net force) without rotating (no...
20. ### Mechanical equilibrium

is an object rotating with no net torque present (such as a sphere spinning about an axis of symmetry) said to be in mechanical equilibrium??