Physics

A 50 kg box falls at its terminal velocity of 70 m/s. At this point, what is the upward drag force, in newtons?

What is the difference between high frequency signals and low frequency signals in terms of the distance that can be travelled by the signal, the power required to transmit the signal (for a certain distance), and susceptability to interference (EMI)? Thanks!

I don't drink coke, but I should imagine they are quite sturdy. I wondered how a lot of this is done but specifically the coke bottle trick. Is it plausible that is having so much strength against force from the outside a coke bottle is week against force from the inside? Much like how an alligator can bite closed with enormous force but can't resist the force of a stout rubber band holding it's mouth closed when attempting to apply opening force.

As summer is here in the UK, I am considering following in the steps of Benjamin Frankin and Michael Faraday by doing an experiment with electricity. There are lots of 400,000 volt supergrid pylons dotted around the English countryside, so why not climb one? As I make my ascent, will I not be protected from a spark jumping across by the faraday cage effect? I have not actually decided to do the climb, am only considering the idea at present.

I have come across the statement that it is more efficient to accelerate a mass at the beginning of a total movement, than later on. So having a mass at rest and wanting to accelerate it up to 10 m/s over 10 s, it should be more efficient to accelerate the mass to 10 m/s earlier on. Why is this?

Hello everyone , I have some questions about standing waves and guitar. In a guitar why is the fundamental frequency the centre of the guitar. Why isn't it just when you play an open string. How do different strings in guitar produce different sounds. Don't they have the same length hence the same frequency. Even though standing waves are produced in the strings when we listen it travels in air. Does this mean the wavelength of the standing waves is different in air or is it the frequency that is different. Thanks a lot!!

I understand sound waves: amplitude and wavelength (or frequency) are rather simple concepts. I understand how sounds travels (in a straight line, and deflected or absorbed by objects). I also read that our vocal cords produce many harmonics, which I suspect is what makes everybody's voice unique. What I don't understand is how you can explain the difference between pronouncing an "A" and an "O", and both at the same frequency. I can see that the mouth makes a different shape, but I fail to understand how the sound waves are affected by the shape of the mouth (amplitude or wavelength of the set of harmonics are changed I guess... since there isn't much else to s…

Hi, Enthalpy means h = u + p.v When, we give heat dq to a closed system at constant pressure p then change in enthalpy dh = dq, where dq = du + p.dv but here only du remains in system, while p.dv is the part which is spended in doing work. Then "Why do we include p.dv in the enthalpy?" -------------------------------------------------- where--- h is enthalpy, u is Internal energy of the System, p is pressure of the system, v is Volume of the system --and system is of Closed Type.

Everybody has seen two-way mirror - transparent from one side, reflective from the second ... isn't that Maxwell's demon for photons? Ok - it's not perfect - it absorbs some photons increasing own heat and emits thermal photons - so it can stay in thermal equilibrium with environment. Let's take a container for photons (covered with mirrors), now place two-way mirror in thermal equilibrium with photon gas inside, dividing container into two parts. The density of photons on the reflective side should be larger than on the second - so it would reduce entropy?

Never mind.

Hello everybody! Can we find the mass of an object from its apparent weight, i.e. what's measured by scales? Thank you in advance!

I have tried to research this through search engines but have come up with very little answers. This question is why I've registered with this forum. I am curious about the behavior of low level infrared and laser beams similar to laser pointer pens and remote controls. Specifically what happens when these low level beams intersect one another at exact or similar wavelengths. Do they ricochet do they pass through do they alter one another? etc. etc. And whatever the differentials may be in their intersection is there a property change when one of the intersecting beams is turned off? Can that be seen as a variable difference in the patterns entirety? An…

I was just wondering, is it possible to focus microwaves using an elliptical mirror?

I was curious as to how a public address (PA) system that operates across a whole school is able to produce signals that allow announcements to be just as loud near the amplifier as they are at the furthest end of the school. I was thinking about my highschool where announcements are made in the main office and will be heard over the whole school even to speakers that are about 200m away. The speakers are all connected in parallel with copper wire, so I was thinking that a lot of the signal strength would be lost as it travels along such a long distance of wire. Any ideas on how they do it?

Hello everybody! My question is about the measurement of mass: Are the American and British pound equal? Do Americans use the Troy pound? Thanks in advance!

I'm new here and probably won't visit often, but I thought I would share my site with everyone as it seems to fit into this category. For anyone who's interested...www.solar-balloons.com Solar balloons are basically hot air balloons filled with ordinary air, which is heated by the sun. The material they are made with is usually black, which absorbs the heat from the sun and in turn heats the air in the balloon. I have released quite a few and my farthest flight yet was over 700 miles. Currently I make them all with the cheapest (thinnest) trash bags and masking tape...you can't get cheaper than that! Once they get up in the air, the sun keeps them heated for the …

http://pubs3.acs.org/acs/journals/doilookup?in_doi=10.1021/ja01269a023 Comparing data to the above PDF file. I do not know which is the Vm value for comparison. My experiment was physical adsorption of gases. The adsorbent used was silica-alumina using Nitrogen gas.

Does anyone have any resource links on the internet that I can read about about how to control a magnetic field, perhaps even do an amateur experiment... It is a topic I am interested in but have not had much luck on the standard google search for "control magnetic field." Thanks, Jeff in Connecticut

I was recently interested by some news that it's possible to drain energy from pure heat. I've read about two ways: use sound resonator or absorb infrared thermal radiation: http://www.physorg.com/news100141616.html http://www.physorg.com/news137648388.html Other problem is for example that while spontaneous crystallization entropy goes in 'forbidden' direction: http://www.garai-research.com/research%20statement/Entropy/Entropy.htm ... It would be nice to localize simplifications of looking to be such general theory like thermodynamics. One way of their reasons can be simplifying physics for thermodynamical model, like - it corresponds to molecules, while we ca…

Hello everyone , I'm so confused with particle displacement vs time graph and pressure vs time graph of sound. I thought maximum displacement of a particle is its compression and minimum displacement is its rarefaction. For some strange reason the graphs show exactly the opposite. How can the particles be at atmospheric pressure when the displacement is maximum. Your help would be greatly appreciated. Thanks

Could you tell me the principle of these vibrations, what they depend on Thanks so much !!!

Can Multiverses be in competition with one another. Working along the lines of 'survival of the fittest'... If matter cannot be destroyed can it change demensions causing universes to expand and contract. Would this relate to the 'Pulsating Theory' of the evolution of the universe, and Dark Matter. Can anyone suggest any suitable reading? Any suitable related forums. Many thanks.

"The reflection from a denser medium causes an additional phase change of pi or path change of lamda/2 while reflection from rarer medium doesn't cause any phase change." can anyone explane me how this happens?

First off... Thank you very much to everyone in this forum who has helped me come to a better understanding of physics. A website has mentioned that eventually the earth will cease to spin and both the earth and the moon will face each other. Tidally locked with one another. What happens after that? Do they collide with each other and form a larger planet? What might the collision ( if that's what would happen ) be equivalent to? Would they merge as one slowly over time? Would they impact with tremendous force and energy and explode? Is there any known observed phenomenon in the universe which demonstrates this on a planetary scale?

Does moisture (in superheated state) improve the performace of a furnace in any way? What are the parameters to be considering when evaluating this? Does the fact that moist air has a higher heat capacity (Cp) have anything to do with this?