General physics discussion thread

[ionbasa]

Gravity is based off the shape of the "space-time" fabric? (According to Einstein.)

[Art Vandelay]

Can anyone explain to me why an imaginary power in a circuit is meaningful?

[ionbasa]

Can anyone explain to me why an imaginary power in a circuit is meaningful?

This is coming from a mechanical engineering student, an electrical engineer may give you a different or better answer.

 

My understanding is that 'imaginary power" is usually referred to as reactive power, and is usually only a factor is AC circuits. Reactive power is usually caused by a high load on a supply with a sine wave (or any trigonometric based wave). Reactance is the opposition of a circuit element to a change of electric current or voltage.

 

Essentially what is happening is that the load is then out of phase by ~90 degrees from the supply. This might be demonstrated through a motor. 

 

Why it matters though is a hard answer. It might be better if you looked at RMS (root mean square) and apparent power. 

 

Also although reactive power could be present in a system, it cannot be converted into 'work', either by mechanical or thermal means.

[Nup]

Any budding mycologists around here?  

Cool thread too  

[thirdworldking]

what are you guys theory on time travel

 

whether it will be possible

 

how could we achieve

 

or just talking about cool stuff like how you dont age much

[iiNrG]

Hm, no I don't think it works like that...

Gravitational fields take on the shape of a sphere, in which directed line segments represent direction. Basic geometry tells us that the closer to the centre, the closer the lines. You will find that the closer you are to the centre of the earth, the stronger the field (as a result of the field lines being closer) same applies to electromagnetic fields etc.

[lucky74dog]

what are you guys theory on time travel

 

whether it will be possible

 

how could we achieve

 

or just talking about cool stuff like how you dont age much

As a fan of Doctor Who, I love time travel. No one knows for sure if traveling to the past is possible, but travelling to the future(faster than normal) has already been done. According to Einstein, the speed you travel in the traditional 3 dimensions is relative to the speed at which you travel in the 4th, time. So, objects at high velocities, such as astronauts on the ISS, move through time faster than everyone else, and going into the future(not by much though). What I think is more interesting about this is how it works with the speed of light. The speed of light is the fastest any object can move in our universe, so, photons of light don't move through time! All of the photons of light are the same age as they were at the begining of the universe! (I learned this in a really nice book I'm reading, "The Elegant Universe". It is mostly about string theory, but, it does give a really nice description of quantum physics, and general relativity. I'd suggest anyone to read it, it's awesome)

[iiNrG]

As a fan of Doctor Who, I love time travel. No one knows for sure if traveling to the past is possible, but travelling to the future(faster than normal) has already been done. According to Einstein, the speed you travel in the traditional 3 dimensions is relative to the speed at which you travel in the 4th, time. So, objects at high velocities, such as astronauts on the ISS, move through time faster than everyone else, and going into the future(not by much though). What I think is more interesting about this is how it works with the speed of light. The speed of light is the fastest any object can move in our universe, so, photons of light don't move through time! All of the photons of light are the same age as they were at the begining of the universe! (I learned this in a really nice book I'm reading, "The Elegant Universe". It is mostly about string theory, but, it does give a really nice description of quantum physics, and general relativity. I'd suggest anyone to read it, it's awesome)

Not sure that's all entirely true. Time is certainly not a dimension, and as for the photon's not moving through time, it's a result of the "higgs field" (But that's another discussion) It IS possible to travel faster than light, and there are a few ways of doing so. Travelling faster than light simply means to be ahead of your frame of reference, and so to "Observe" the future. One of my personal favourite methods is through "Negative energy", in which many strange things can happen;

Temperature Below Absolute

Negative Pressure

But the best example is light travelling faster than in a vacuum (Since vacuum's DO have energy, although miniscule, look up "Hawking Radiation")

Negative energy can theoretically be created by using the Casimir Mechanism (Again, Hawkings radiation comes into play here)

[erty176]

When dealing with electric fields, why is flux through the center of an object zero?

[lucky74dog]

Not sure that's all entirely true. Time is certainly not a dimension, and as for the photon's not moving through time, it's a result of the "higgs field" (But that's another discussion) It IS possible to travel faster than light, and there are a few ways of doing so. Travelling faster than light simply means to be ahead of your frame of reference, and so to "Observe" the future. One of my personal favourite methods is through "Negative energy", in which many strange things can happen;

Temperature Below Absolute

Negative Pressure

But the best example is light travelling faster than in a vacuum (Since vacuum's DO have energy, although miniscule, look up "Hawking Radiation")

Negative energy can theoretically be created by using the Casimir Mechanism (Again, Hawkings radiation comes into play here)

What I described was not the whole picture ,obviously, and I am pretty sure that time being a dimension was only created to help visualize what is happening.  I definitely take a look at those though. What if it was possible to go back in time (Now)? Lets discuss some of the paradoxes! Paradoxes are fun.

[NerdNinja]

What I described was not the whole picture ,obviously, and I am pretty sure that time being a dimension was only created to help visualize what is happening.  I definitely take a look at those though. What if it was possible to go back in time (Now)? Lets discuss some of the paradoxes! Paradoxes are fun.

This thread is gonna call ALL the whovians of the LTT forum! As far a paradox? I got an example! You go back in time and kill your young self on accident. Now do you still exist? Or will the future self of you disappear for never being born but then you will have never existed to come back and kill your young self and thus your young self would have survived up to you? 

Let's discuss.

[Guest]

What do you mean by that?

What is nothing

[Art Vandelay]

This is coming from a mechanical engineering student, an electrical engineer may give you a different or better answer.

 

My understanding is that 'imaginary power" is usually referred to as reactive power, and is usually only a factor is AC circuits. Reactive power is usually caused by a high load on a supply with a sine wave (or any trigonometric based wave). Reactance is the opposition of a circuit element to a change of electric current or voltage.

 

Essentially what is happening is that the load is then out of phase by ~90 degrees from the supply. This might be demonstrated through a motor. 

 

Why it matters though is a hard answer. It might be better if you looked at RMS (root mean square) and apparent power. 

 

Also although reactive power could be present in a system, it cannot be converted into 'work', either by mechanical or thermal means.

If I remember my circuits class correctly, imaginary power is a factor on AC circuits with loads that can store energy. 

 

One of the students asked the prof why imaginary power was meaningful, and the prof told us it was out of the scope of our course.

[Akhilsharma]

well gravity is almost constant throughout the earth surface horizontally and even at high peaks as mt everest.
teh gravity at poles is about 9.7968 m/s^2, which is max value of g. where as at the base of Mt. Everest it would be about 9.7705, which is just 0.0263 m/s^2 less. moreover at the top of Mt. Everest the value of g would be at 9.7569 m/s^2 which is about 0.04 m/s^2 less than the maximum value and just 0.0136 m/s^2 less than that at it's base. considering the differences we can say that these negligible values would not affect much however if your mass is not a great deal as weight=mass*g
So a person of about 100 kgs can experience some change in his wieght about a killogram less than his weight at the base of the mountain but yet it would be negligible for him(100-1=99).
i think this explains it yet if i missed something do let me know.