Scientific 'things you've always wanted to know' thread

[R300will]

tank slapper said:

Jandywa said:

The gravitational pull of the sun on the earth is greater than that of the moon. So why is it the moon that affects the oceans and not the sun?

The sun does affect the tides - it forms about a third of the total effect. The moon affects the tides more obviously because it is closer and orbiting us. As it proceeds around its orbit, its position relative to the sun changes. When the moon is in roughly in line with the sun, on the very inside or outside of its orbit then the tides are at their highest (new moon and full moon), called spring tides. When the moon is half way between, the tides are at their minimum and are called neap tides.

Since orbits are elliptical and not circular, the moon earth and sun are all moving slightly closer and further away from each other. This also has an effect on the tide height. Spring tides occur roughly every 2 weeks, and the orbit of the earth around the sun causes the height of the spring tides to slowly increase and decrease throughout the year. The very highest tides are when the moon and sun are aligned, and when the earth is closest to both the moon and the sun.

What would be the difference between january and june high tides? assuming the moon is in the same position so relying on the sun entirely for the rest of the effect. The earth is closest to the sun in january i believe.

[tank slapper]

R300will said:

What would be the difference between january and june high tides? assuming the moon is in the same position so relying on the sun entirely for the rest of the effect. The earth is closest to the sun in january i believe.

I'm not sure what the effect is purely from the orbital eccentricity of the earth. In theory the highest tides might occur at the beginning of January, but that can easily be masked by the moon being in a different alignment as the lunar effects tend to dominate. The absolute highest tide would occur when earth is closest to the moon, the moon is closest to the earth and the moon happens to be aligned with the sun. As all those things have different periods it won't be every year that occurs. I know that when tide tables are produced they can use a huge number of periodic constants to get the final curve, so you'd probably need a hydrographer to tell you exactly.

[rxtx]

MOTORVATOR said:

But the tides happen on both sides of the earth slightly unequal which is why there is a variation between tide heights within a day. Centrifugal force in a reduced gravity situation is what causes the other side and gives the 2 tides within 25 hours. (One orbit of the moon).

One earth rather than moon orbit

[MOTORVATOR]

rxtx said:

MOTORVATOR said:

But the tides happen on both sides of the earth slightly unequal which is why there is a variation between tide heights within a day. Centrifugal force in a reduced gravity situation is what causes the other side and gives the 2 tides within 25 hours. (One orbit of the moon).

One earth rather than moon orbit

Git. One orbit of the moon around the already spinning earth?

[rxtx]

MOTORVATOR said:

Git. One orbit of the moon around the already spinning earth?

No, because it takes the moon 27.3 days to orbit the earth, assuming a sidereal month, slightly longer for a synodic month.

[MOTORVATOR]

rxtx said:

MOTORVATOR said:

Git. One orbit of the moon around the already spinning earth?

No, because it takes the moon 27.3 days to orbit the earth, assuming a sidereal month, slightly longer for a synodic month.

Lunar perigee-syzygy cycle.

[WCZ]

would this be possible?

[SkinnyBoy]

WCZ said:

would this be possible?

http://www.daviddarling.info/encyclopedia/D/Dysons...

[speedy_thrills]

WCZ said:

would this be possible?

ITER aims to do just that by making a small sun. For reasons that are inexplicable to me, given that if successful humanity would be catapulted forward, they seem to have a hard time getting research funding.

[annodomini2]

speedy_thrills said:

ITER aims to do just that by making a small sun. For reasons that are inexplicable to me, given that if successful humanity would be catapulted forward,

It's not a small sun it's a controlled nuclear fusion reaction. The plasma is shaped like a doughnut

speedy_thrills said:

they seem to have a hard time getting research funding.

ITER and the Tokamak design are never ending money pits imo. Their budget is ridiculous 20billion or something stupid.

Not to mention the amount that has been wasted on JET and the like.

The main issue with Nuclear fusion is getting a net energy reaction. (i.e. more out than in! )

There are other concepts out there that appear to be achieving much more, on much smaller research budgets.

My personal favourite is Focus Fusion. Which is an Aneutronic DPF concept.

The key part there is the Aneutronic or in conventional terms, without neutrons (neutron radiation!).

The concept reaction used in ITER produces lots of neutrons, those neutrons are used to heat water into steam and generate power in the conventional method.

The main issue with this is it can be used for Nuclear proliferation (the high energy neutrons can be used to help create fissile material for nuclear weapons)

The Focus Fusion concept uses a different fuel, produces almost no neutrons (relatively), the primary output products are helium ions and electrons.

The benefit of this is as the charged particles come away from the reaction in a perpendicular streams (think pulsar) passing the ions through an electrical coil allows for direct electricity generation. i.e. no steam turbines required.

This all makes the system much more efficient.

[Nimby]

SkinnyBoy said:

http://www.daviddarling.info/encyclopedia/D/Dysons...

A Ringworld would be nicer to live on. Shadow squares give day/night cycles, and you can see the stars.

http://en.wikipedia.org/wiki/Ringworld

[speedy_thrills]

annodomini2 said:

The main issue with this is it can be used for Nuclear proliferation (the high energy neutrons can be used to help create fissile material for nuclear weapons)

I'm not that concerned about Iran having their own version of the ITER project. Much of their "research" work is highly derivative of work done in the 1940's so maybe in 2070 I'll regret that.

Agreed on exploring every avenue.

[annodomini2]

speedy_thrills said:

annodomini2 said:

The main issue with this is it can be used for Nuclear proliferation (the high energy neutrons can be used to help create fissile material for nuclear weapons)

I'm not that concerned about Iran having their own version of the ITER project. Much of their "research" work is highly derivative of work done in the 1940's so maybe in 2070 I'll regret that.

Agreed on exploring every avenue.

You don't need a large reactor like ITER to create this effect is the biggest issue. Although the larger volume of neutrons from the reaction with a reactor like ITER or JET makes it easier.

[hairykrishna]

annodomini2 said:

My personal favourite is Focus Fusion. Which is an Aneutronic DPF concept.

The key part there is the Aneutronic or in conventional terms, without neutrons (neutron radiation!).

The concept reaction used in ITER produces lots of neutrons, those neutrons are used to heat water into steam and generate power in the conventional method.

The main issue with this is it can be used for Nuclear proliferation (the high energy neutrons can be used to help create fissile material for nuclear weapons)

The Focus Fusion concept uses a different fuel, produces almost no neutrons (relatively), the primary output products are helium ions and electrons.

The benefit of this is as the charged particles come away from the reaction in a perpendicular streams (think pulsar) passing the ions through an electrical coil allows for direct electricity generation. i.e. no steam turbines required.

This all makes the system much more efficient.

Attempting to go straight for aneutronic fusion seems crazy. It's so much harder to do boron fusion than DT and DT's hard enough to do at greater than break even. Your proliferation argument makes little sense - if somewhere has the tech to fuse boron they can do neutron producing fusion all day long if they so desire.

I always thought the best idea for a fusion reactor would actually be a combined fission-fusion device. Wrap a sub critical fission reactor assembly around a tokamak solves the energy extraction problems and gives a nice efficiency boost.

[Ayahuasca]

Eric Mc said:

Sway said:

Eric - if you watched these things for 5 minutes you'd realise there's not a chance little JK is the Newton of his species. He has no greater joy in his life than a used toilet roll core, and yet he's a cheery little chap.

I have it on good authority that Sir Isaac could have hours of fun with a tube of cardboard - especially if it had a couple of gerbils in it.

Sir Isaac too? I thought that was just Richard Gere!

[annodomini2]

hairykrishna said:

annodomini2 said:

My personal favourite is Focus Fusion. Which is an Aneutronic DPF concept.

The key part there is the Aneutronic or in conventional terms, without neutrons (neutron radiation!).

The concept reaction used in ITER produces lots of neutrons, those neutrons are used to heat water into steam and generate power in the conventional method.

The main issue with this is it can be used for Nuclear proliferation (the high energy neutrons can be used to help create fissile material for nuclear weapons)

The Focus Fusion concept uses a different fuel, produces almost no neutrons (relatively), the primary output products are helium ions and electrons.

The benefit of this is as the charged particles come away from the reaction in a perpendicular streams (think pulsar) passing the ions through an electrical coil allows for direct electricity generation. i.e. no steam turbines required.

This all makes the system much more efficient.

But that's the problem, they've been trying for over 50 years to get a Tokamak to break even spending more than the GDP of a small country over the years.

LPP have made some good advances over the last couple of years, maybe the Tokamak is the wrong solution, you state yourself that you don't think it's the ideal solution.

Also direct generation vs thermal,

Thermal requires a 3-5x minimum energy gain to be cost effective due to conversion efficiencies.

Whereas Direct only requires 2x to be cost effective.

Attempting to go straight for aneutronic fusion seems crazy. It's so much harder to do boron fusion than DT and DT's hard enough to do at greater than break even. Your proliferation argument makes little sense - if somewhere has the tech to fuse boron they can do neutron producing fusion all day long if they so desire.

I always thought the best idea for a fusion reactor would actually be a combined fission-fusion device. Wrap a sub critical fission reactor assembly around a tokamak solves the energy extraction problems and gives a nice efficiency boost.