# danny8522003

Senior Members

320

1. ## What happens when photons interfere?

Would it not just reflect off the sunny side of the disk?
2. ## quantum entanglement help

An example of quantum entanglement results from the creation of two photons from a positron-electron annihilation event. The two photons emitted in each opposite directions are related through certain observables. By measuring an observable of one you, by definition, know the value of the observable of the other.
3. ## Fourier Series

I know i can't change the title but i solved the problem i was looking for originally and need help with another... The question says to use an integrating factor to solve: x(dy/dx) = y + (y^2)x The problem comes at the very last part to find v' and v because of the y^2 term. The factor i'm using is: y = v*exp(-integral[-1/x]dx) where the -1/x is the term infront of the y when you divide by x and bring it across. Any pointers would be great. Thanks.
4. ## black hole gedanken

Spaghettification of the string and weight, but what properties does the sting have? Can it stretch, take an infinite force before breaking etc...
5. ## Question re. Brownian movement

Sorry i meant negligible. It was late.. I was tired..
6. ## The Hammer and the Feather

If you drop them at the same time, they impact at the same time. If you drop them separately then they take different amounts of time to fall? I'd never thought about that overlap before, of course that would happen because of the overlapping 'gravitational field' of the 3 objects as they all attract each other. Although to be even more picky, i didn't say that they were dropped on the same hemisphere .
7. ## The Hammer and the Feather

Thanks, knew it was there somewhere!
8. ## Question re. Brownian movement

Actually the lost energy is thought to be given off as gravity waves or gravitons. Just as an electron would give off photons as it orbits a nucleus, and hence puts rest to the Bohr model. It's interesting to see how energy is gained and lost but is inevitably conserved. Glad I could be of help.
9. ## The Hammer and the Feather

Just to be picky... Two objects of different masses falling in a frictionless environment wold not hit the ground at the same time. The effect is however so tiny when you do it on the moon or the Earth that it's impossible to measure. My tutor derived an equation that included the 'reduced mass' to calculate the acceleration due to gravity, but i can't remember it off hand. I also can't find the wiki article that contained it.
10. ## Brake failure from heat

Some more info on the subject: http://en.wikipedia.org/wiki/Brake_fade My brakes failed once when i was going down a hill, when i got out the car there was smoke coming from the wheels. Thank heavens for engine braking.
11. ## Question re. Brownian movement

The motion of the pollen is due to water molecules colliding with them creating movement through conservation of momentum. These water molecules lose energy and give it to the pollen, and hence no energy is lost from the system. The motion of the planets is not perpetual since energy is conserved. The rotation is due to the fact the matter the solar system is made of was rotating before it collapsed. The planets actually lose energy as they orbit the Sun but this is arbitrary and is not noticable.
12. ## Vocabulary: Unability to scale difference

immeasurable?
13. ## Tricky friction problem

There is no force acting to prevent the movement of the lower block because of the frictionless table though. Any force greater than 0 will give rise to an acceleration in the lower block. In order to prevent the lower block from accelerating at 3.5m/s wouldnt there need to be a force opposing this acceleration in the form of friction? Any force on the upper block will result in a force on the lower block, but how can it exert a force back if there is nothing opposing acceleration but it's own inertia?
14. ## Tricky friction problem

If the table is frictionless, then any mu value greater than 0 between the blocks would mean they would both accelerate at 3.5m/s. Surely?
15. ## Kinetic energy and blackholes

Gain in kinetic means loss in potential... Just because it's a black hole, it doesnt act any differently than say the earth. (Not taking relativity into account)
16. ## Curses upon all Malware writers

If we know the names of the companies that implement the malware (cool web search for example) .. Why can legal action not be taken against them? Failing that, im sure there are lots of 'hackers' that want them taken down so a voluntary DDoS attack would be simple to start and would get rid of the blighters. I sure as anything wouldnt mind contributing my upload for a good cause such as this... By hackers i mean real hackers, not scriptkiddies and the like...
17. ## Binding Energy

Thank you. Just confused me having the rest mass change while it's stationary both in and out of the nucleus, stupid quantum physics
18. ## Binding Energy

But it's at rest..
19. ## Binding Energy

Hey guys, Doing a project on star formation and fusion. We did mass defects in class today, but we were using ${\Delta}E={\Delta}mc^2$. Seeing as the mass is the rest mass of an object, can this be applied to protons when they are both at rest and in the nucleus? Thanks, Dan
20. ## Relationship between Planets size, mass, age and gravity?

Would probably be easier to model it as a sphere. Humans have barely any gravitational pull so you wouldn't really need it for any useful purpose anyway.
21. ## Relationship between Planets size, mass, age and gravity?

$g = -\frac{GM}{x^2}$ for mass m and distance x. Saturn may have a greater mass, but some of it's mass is far away due to the planet being a large sphere. Age does not affect gravity afaik unless m or x increases or decreases with time.
22. ## Graviton question

I'm no expert, but i would have thought that gravitons stay as they are. Gravitons are exchange particles, if there is nothing to exchange these with then they'd just stay in the original mass so to speak. Right?
23. ## Error Message

Might have just been a javascript box set up as a joke...
24. ## Great Search Engine

Doesn't work in Opera either ...

Where m > 0.
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