Sisyphus

It does not "need" a continuous input of energy to keep moving. That's what I'm trying to say. (Also, photons are not "made of" energy, but that's less immediately important.)

What is the minimum speed to avoid orbital decay at Earth's distance from the sun, then? How do you calculate that, btw?

"Orbital decay" in the sense of satellites slowing down and crashing to Earth is caused by the tiny amount of friction with the upper atmosphere. In the absence of some outside force like that, orbits don't decay. In order to crash into the Sun, you would just have to get yourself into an orbit that intersects with the Sun's surface. Starting out from the Earth, that would mean a great deal of acceleration to get rid of almost all of the relative velocity you started with. So in other words, you would go from being in an almost circular orbit, to the apogee of a very eccentric ellipse.

EDIT: Here's a drawing:

The Earth (E) orbits the Sun (S) in a nearly circular orbit (blue), with a certain amount of perpendicular velocity. Increase that velocity at that same point, and you are in an elliptical orbit and starting at the perigee (red). If you increase it enough, the ellipse never closes, and you escape. Decrease it, and you're at the apogee (green.) Decrease it enough, and the orbit intersects with sun itself (orange). This is all starting from the same point and with velocity in the same direction, but of different magnitudes.

I already said why it was wrong. Your unstated premise, that things lose energy just from moving, is not correct. There is no such thing as "losing energy to motion."

Why should it be hard to get to Venus, Mercury, or the sun? It's downhill. If you escape Earth orbit in the opposite direction so that your speed is slightly less than that of Earth, shouldn't you begin to fall toward the sun the same way a satellite that loses speed begins falling toward Earth?

No, you'll just have a slightly smaller and more eccentric orbit. You won't fall towards the sun unless you get rid of almost all of the velocity you started with (the Earth's orbital velocity), which is the same as adding the difference. (Delta V is delta V.)

Things don't lose energy just from moving, though.

Well then why don't they teach us that in schools?

They do?

Also sound should never be classed an an energy...not even as a manifestation of kinetic energy...

Whyever not?

So...According to wikipedia and just about every other source there are 10 types of energy...

No. Those are just examples of various manifestations of energy. That list is not complete nor are they mutually exclusive. e.g. "sound energy" is just a macroscopic manifestation of kinetic energy of individual particles. In fact, they're all various forms of kinetic or potential energy, as the very next sentence in the Wikipedia article points out:

These energies may be divided into two main groups; kinetic energy and potential energy.

How did you get 6.6 years?

Wasn't my figure, but:

10mph is about 16 kmph.

There are 24*365= 8760 hours in a year.

16*8760 = 140160 km per year.

925000km / 140160 km per year = about 6.6 years.

Why is more fuel required? I would have thought it would be about the same. For example, I always thought that walking a mile or running a mile burned about the same number of calories since you are moving the same mass the same distance (ignoring thngs like efficiency of movement).

Because you're fighting the same gravity for hours or days instead of minutes. The analogy is more like walking or running against a treadmill for a distance of a mile. (That is, you're at the other end of a mile long treadmill, not that a mile of tread has passed under you.) It takes 1g of thrust just to hover, which is actually quite a bit. Your acceleration upwards is from the excess over that already considerable thrust.

How would you define "sweatshop?"

 

 

Well, maybe it is putting this thread out of track, but:

 

the programmers of Autocad (which is an extremely evolved vectorized mathematical program) were not able to conceive the analog command ("Scale") without the input of a base point.

 

Commands go like that:

Command: scale

_select objects

_specify base point

_specify scale factor

[enter]

 

And indeed, without the base point, how could the program execute the scale factor? Scaling cannot be done with multiple base points.

Indeed, what we observe can't be rendered in simple Euclidean space, such as is depicted in autocad. That's one reason for the common misconceptions, since people are used to thinking that way.

Well personally, I never get fountain soda (because it's gross) in the first place, so I save even the "small" price. I've heard that's where they make most of their money, since the profit margin is so huge. That crap is dirt cheap, which is why they can offer free refills and not worry about it. Perhaps the shrewdest choice is not based on maximizing the amount of soda you consume. Just drink tap water - it's bad enough you're eating McDonalds!

But I'm curious - if you get free refills, why not get ice?

I always take a 0.5 liter (that's the "large" in the Netherlands). I know that "large" has different definitions in different countries.

Oh, goodness. That's as as small as you can get in some places. Here in America we have 7-Eleven, that sells 64oz (about 1.9 liter) size fountain drinks.

Does this mean that the weak force is only present in elements heavier than iron and only the strong force is present in iron and lighter?

No. First of all, the conflict is between the strong force which holds things together and the electrostatic force which wants to force things apart. The strong force is stronger but shorter range, which makes it more dominant in a smaller nucleus but less and less so as the nucleus gets larger.

Yes swansont, you have right points. There are some animals which have natural tools on their body to protect and feed theirself, so there is no pressure on them to change theirself. Moreover, depth perception is very important for discovery. If I add a point, I think "having hands" is a very big advantage to be able to develop tools.

 

According to the properties above, apes are very suitable to develop theirself. However, it is coming to same point again. Million years ago, humankind and many other ape kinds had similar brain, similar body properties and characteristics, similar living style, similar threats from other wild animals. What did push humankind to develop new tools and to discover new living tehcniques? Why didn't other apes feel the same pressure although we had similar life and threats?

They did. Neanderthals had language and complex tools comparable to our ancestors contemporary to them. Clearly, it didn't save them from extinction. Chimpanzees and bonobos, our closest surviving cousins, have only very basic tools and are doing fine. Or they would be, if they had no interaction with humans.

I think the thing it's important to remember is that what gives humans such a tremendous advantage is civilization, but that isn't necessitated by our big brains, only allowed by it. Civilization is only a few thousand years old, which means that it didn't exist for the vast majority of the history of biologically modern humans. The natural ability to learn to manipulate the environment as well as we do is still an advantage "in the wild," but much, much less of one, with all the same disadvantages.

So the intelligence of humans is really a freak event - a series of coincidences allowing a minor advantage in limited circumstances... that eventually became an unprecedented advantage. But "future advantage" cannot be a driver of evolution.

Empirical demonstration is "begging the question?"

The reaction mass is not theoretical limit. p=mv is a Newtonian equation, and you'd be dealing with relativistic velocities. A gram (or a single atom) of He moving at C would have infinite momentum, and in theory I'm pretty sure you could give it arbitrarily large momentum.

Rather, the limit is the energy needed to accelerate the reaction mass... the generation of which in turn consumes mass. So I guess the limit would come from generating the energy that would be transformed into kinetic energy of the reaction mass.

The poll is about the impact of pundits on politics. Politics in a democracy is all about the manipulation of public opinion.

Does the poll demonstrate successful manipulation of public opinion? I'd say at most, it shows manipulation of public opinion about pundits. They've managed to convince people that they have an impact.

Or maybe not! The only options were positive impact, negative impact, and never heard of 'em. I think the answer is more likely to reflect "do you agree with this person," which is not the same thing. I can agree with you and think you have no impact at all (not a choice!), because you don't change anyone's mind.

Term limits in general are anti-democratic, but I still wouldn't want to get rid of them. In fact, I'd like to see term limits for legislators.

But I guess that's not with this thread is about. The first alternative that comes to mind for me is the system in the Roman Republic (the whole Roman Republic was pretty much based on making it hard for one person to gain monarch-like powers), where the consulship and various other offices had restrictions against consecutive terms, but not on number of terms. In theory this would make it a lot harder to establish the kind of entrenchment that term limits are designed to protect against, but it wouldn't force a good politician to go away forever. This would work best on offices with short terms (the Roman consulships had terms of one year).

On the other hand, I can easily see how the spirit of such a restriction could be circumvented. You'd really just need two allies assuring the electorate and the monied interests that each is effectively a continuity of the other, alternating holding office, so it's a de facto dually held office with almost the same level of entrenchment.

So 1g of matter is convertible to 25,000 kwh of electricity at 100% efficiency, regardless of what type of matter it is? So a fusion reactor that would convert hydrogen to helium would only deplete 1g of mass per 25,000kwh generated? So how would you figure out how much mass is lost in the conversion? Is this also explained by E=MC^2 or does that require attention to the internal structure of the atoms in question?

That would be 25,000,000 kwh, not 25,000. And yes, you need to know the masses of H and He to figure out how much you'll be going through.

You are correct, basically. A very, very tiny percentage of the photons emitted by the star hit the Earth, and that percentage is inversely proportional to the surface area of a sphere with a radius the distance between the star and the Earth. The reason we still see it is just because the star is throwing out many, many, many, many photons in every direction, so you still see a constant stream of them, even though you're so far away and an extremely tiny percentage of them enter your eye.

DH,

 

Which is nonsense; Having smaller solar tides or having two sets of tides.

 

How many centers of gravity a single body may have?

The Earth has 1 center of gravity, but that's irrelevant. Tides are caused by gravitational gradients. In other words, the difference between the force of gravity on the near side of the Earth and the far side.

The Sun's force of gravity on the Earth is obviously much greater than the Moon's. However, the force of gravity at high noon and at midnight (near side and far side) is very close. By contrast, the difference between the attraction of moon on the side of the Earth closest to the moon and the side farthest away is much greater, largely because the moon is so much closer. That's why lunar tides have more of an effect than solar tides.

Ok, thanks, I think I'm getting it. So if I use m/sec for C, which is 300k, then I should use 1/1000 for 1g. 90000k/1000=90000 joules, which would convert to kwhours by 90000/3600000, which is 0.025. That doesn't sound like much energy though. That's 25 watt-hours, which wouldn't even run a cfl lightbulb for two hours. Did I do something wrong?

Couple things. The speed of light is not 300k meters per second. It's 300 million meters per second. You also didn't square it correctly. 300k*300k is not 90000k - that's just 300k*300.

So, 300,000,000m/s squared is 90,000,000,000,000,000, making your answer off by a factor of 1 billion. It will run a CFL bulb for two billion hours.

These units confuse me. Speed = distance * time makes sense to me because it is a rate of change in distance. Likewise, momentum = mass * velocity makes sense to me because a fast moving light object can transfer its momentum to a heavier object to produce a lower speed. Power = force * distance makes sense because it makes sense to define power as continuously applied force. But how do these units for energy make any intuitive sense? Why is the distance divided by time? Are they just squared to avoid having to plug a negative number into the denominator? Is there any logic to defining what energy is in a qualitative sense? To me, energy (kinetic) is particle momentum, so it should be in mv units.

 

edit: I just remembered that force over a distance is work, not power. sorry for the mistake. no need to point out my mistake. it was just an example of an intuitively intelligible physics concept.

It makes intuitive sense if you work up to it.

Velocity is distance/time.

Acceleration is velocity per time, so distance/time^2.

Force is mass*acceleration, so mass*distance/time^2.

Energy is force through a distance, so mass*distance^2/time^2.

That makes sense, but how does C work since it's a speed? How do you multiply 1 gram by C^2? Does energy come out in force per unit distance (i.e. power)?

Energy is in units of mass*distance^2/time^2. For example, the definition of a joule is 1 kilogram times 1 meter squared divided by 1 second squared.

It isn't the same as power. Power is energy per unit time, so mass*distance^2/time^3. (1 watt is 1 joule per second.)

I would say they are both rape, because it's sex against a person's will. That's what rape is. That they were having consensual sex before it was non-consensual doesn't change that.

The second case would be hard to accuse as extortion on her part, at least legally, but is definitely rape on his part if he continues against her will. Again, it's no different than if I change my mind after I got my job and then demanded more money for my labor contrary to our contract. If my boss forces me to continue my labor, that's slavery. If I force the increase in pay, then I'm in violation of our contract and he's free to dismiss my services altogether.

I don't think that would be slavery unless your boss was physically forcing you to work. You agreed in a legal contract to do X work for Y pay. You owe X work. Similarly, that prostitute owes the customer sex for the agreed upon price. However, I agree that it's still rape if she changes her mind. Violation of a contract does not grant you the right to take what you think is owed to you by force.