# mistermack

Senior Members

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14

1. ## Basic Conservation of Energy Problem

I don't think you can assume the spring is rigidly fixed, for momentum purposes. If you do, momentum can never be conserved.
2. ## Basic Conservation of Energy Problem

I'm not sure that you can use momentum in this case. You aren't told what the spring is attached to. So how do you calculate the momentum of an unknown object? I think the question is an idealised one, about kinetic energy, without the losses that you know will actually happen. Dunno why he gets the wrong answer though.
3. ## Why are female chimps not selective about partners

In your sheltered world, maybe. In chimp society, if you are at the bottom of the pile, you are last to eat. Which is life-threatening in scarce times. And chimps are very violent. There are no police to protect you. In the jungle, just one bite can get infected and kill you. You need friends to survive in chimp society.
4. ## Sinking of the Titanic

Your own linked engineering review says nothing about a fire weakening any part of the ship, and it shows the six slits opened up by the ice, all well below the water line, which have been established by modern accurate sound mapping of the wreck. There is no mention of any hole above the water line, and in any case, that would be irrelevant to the sinking. The fire theory really is not supported by the facts. As far as materials go, the sister ship of the Titanic was in service for many years, surviving numerous collisions, including being hit by a warship, and ramming and sinking a UBoat. It's materials were what was commonly available at the time. If the fire was so intense as to weaken the hull, you would think that the cabins immediately above it might have got a bit warm. There's no mention of any of that in any of the history. All the evidence points to a fairly routine fire, that was a common occurrence in coal bunkers of steam ships at the time, which was dealt with and put out before the collision. And I'll say again, there is no way that steel plate, with the entire Atlantic ocean on the other side, just 3cm away, could reach any temperature much above freezing. It's actually likely that the cold made the steel more brittle, not high temperatures.
5. ## Sinking of the Titanic

Any citation available for that? It seems at first sight to be highly unlikely, as 90% of an iceberg is under water, and if it had vertical sides, it would just flip over. The wiki article says that it was holed below the waterline, as you would expect. In any case, holes above the water line wouldn't sink the Titanic. I don't see any way that the hull below the water line could get even warm. You could put an oxy-acetylene torch on your kettle, but if the water inside was constantly changed, with water just above freezing, you wouldn't even get it slightly warm. These low-oxygen fires are not infernos, they smoulder due to lack of air, and the only reason they can't put them out is that they can't get at them.
6. ## What am I observing?

"According to present-day understanding of what is called the vacuum state or the quantum vacuum, it is "by no means a simple empty space",[1] and again: "it is a mistake to think of any physical vacuum as some absolutely empty void."[2] According to quantum mechanics, the vacuum state is not truly empty but instead contains fleeting electromagnetic waves and particles that pop into and out of existence.[3][4][5]" https://en.wikipedia.org/wiki/Vacuum_state
7. ## Sinking of the Titanic

I really don't see the logic of this argument. It's a most unlikely scenario. Firstly, the fire was out, according to Wikipedia. Secondly, the ship was holed below the water line. The hull was made of steel plate, 3cm thick. Outside of that was the cold sea, constantly refreshed at over 20mph. Even if the temperatures of the coal reached 2,000 degrees, it would have little effect, against the chilling effect of the sea. Even well above the waterline, it's doubtful if the steel could get very hot, with the cold damp weather in the north Atlantic, and regular sea spray. If it did get that hot around the water line, it would have constantly created huge clouds of steam that passengers would have surely noticed and mentioned.
8. ## Sinking of the Titanic

I had a look at the Titanic page on Wikipedia, and it seems that there was a fire burning in one of the holds, but it's been known all along, and was a very common occurrence in big steamships at the time. It wasn't a huge fire, and was put out well before the collision. Fires used to start spontaneously but they were like a fire in a hay-rick. Due to the lack of oxygen, they smouldered, rather than blazed, but were hard to get at, because of the tonnage of coal that you would have to move, and were controlled, rather than eradicated. As the stock of coal reduced, it got easier to access the fire. That's why they burned for days. It was the best way to handle them. As far as weakening the rivets, how does that work? The rivets are heated to high temperatures when they are fitted. That's how they work. How does heating them again weaken them? Assuming that we believe wikipedia when it says that the fire had been out for several days, by they time they hit the iceberg.
9. ## i need some validation to an idea I have

It think the speed of light being a constant, and it being a constant for all observers, are two different questions. If you imagine a train that always travels at a constant speed which cannot vary, that is one thing and would have a certain physical explanation. But if the same train always travelled at the same speed for all observers, that is a very different phenomenon, and would require time to be different for each observer.
10. ## Giant kelp farms to save the world!

I just watched a repeat of "Wild China" on the BBC. It was the episode about the coast, and I'd forgotten that it contained an item about a gigantic kelp farm. There were floating supports as far as the eye can see, dangling ropes with kelp growing off them. It's a traditional industry that's been going on for a long time. Saccharina cultivation in China Saccharina japonica (formerly Laminaria japonica) is the most important economic seaweed in China. Mariculture on artificial floating rafts started in 1952, apparently using plants from populations introduced accidentally from Japan), and production increased steadily until 1980 when the production of 200,000 dry tons (about 1,500,000 wet tons) were achieved. In the late 1980s, the cultivation area and total yield declined due to the development of shellfish culture as farmers preferred cultivating shellfish to kelp. Currently, the yield of kelp from about 200,000 acres of farms is about 250,000 dry tons from about 2,000,000 wet tons, worth about 2 billion Yuan (Dr Zi-Min Hu, pers. comm.). So it's not such a new idea. It's been going on all of my life. The economics are obviously not overwhelmingly good, or it would be taken up on a bigger scale around the world. http://www.seaweed.ie/aquaculture/kelp_china.php In the same episode of "Wild China" they showed the Chinese fishing for jellyfish. They are catching them in large numbers, and are eaten as a common food all over China. With the increase in plankton due to pollution and over-fishing of predators, jellyfish are booming in numbers and they are catching increasing numbers. Another possible industry based on plankton blooms.
11. ## What am I observing?

We get the same effect when trying to see the planets orbiting other stars. Even though we know that they're there, by the wobble in the star's position, or the regular dimming if the planet actually crosses the face of the star, we can't see them by the reflected light of the star. They would be shining locally very brightly, just like Venus or Jupiter here in the solar system. But we can't see them, even with the most powerful telescopes ever built. The light from the stars just drowns out the light from the planets. They are too close together, and the reflected light is too dim to make it to Earth in usable amounts.
12. ## Why are female chimps not selective about partners

Chimpanzees live in large-size troops, rather than the smaller family groups of Gorillas, or even smaller ones of humans. The social relationships are complicated, and there's a lot of making of allies, as a form of protection. Mating with lots of males can gain a female protection in the group, and it can be a form of insurance against falling out with one faction. And if several males view the offspring as their own, it helps with protection against bullying later. Male Chimpanzees often get very jealous, and make extreme efforts to monopolise a female. His interests don't really match hers. Chimps have huge testicles, compared to humans. That reflects on the females being relatively promiscuous. More sperm means you might be flushing out someone else's sperm, and makes it harder for them to flush out yours. So it looks like female chimps have been promiscuous for a long long time. It seems to work for them.
13. ## What am I observing?

As far as I can make out, cosmologists are arguing that space is expanding, but they have absolutely no idea how or why. It's just something to say, to match the observations. But there's nothing I've heard of in physics that explains how space between objects can be increased, without a source of acceleration. If we don't know something, I think it should be made clear or it just leads to confusion. We don't even know WHERE the extra space is added. It can't be that the existing space is just getting bigger, because that would make everything bigger, and there would be no way of detecting it. So it seems that space between matter gets bigger, but particles don't grow. Maybe it leaks in from other dimensions.
14. ## Solid state battery announced

It sounds too good to be true. But I hope it is true. It would change the world, if it is true, The materials are not rare, and sound re-usable. So if it has the advantages claimed, it would enable electric vehicles to really take off. Forget phones and laptops, its cars and trucks that would have the most impact on the world. If the energy density is higher than Lithion, then the weight would be much reduced, and electric buses, cars, trucks and bikes will be everywhere. And if the price was less than lithium, that would impact on energy storage, and make home wind and solar a more practical proposition. That's why it sounds too good to be true. I would expect a bigger noise to be made about it, if it's really as good as it sounds.
15. ## Sinking of the Titanic

An enormous fire burning in the bowels of the ship would create enormous heat, would prevent the normal operation of the engines, would make a lot of noise, and huge quantities of smoke. (since the crew would be pumping sea water at it to try to put it out). Funny none of the survivors noticed any of it, and the ship was making very good time, (wasn't it going for a record, or something?) It all makes the fire story pretty unlikely to me.
16. ## Injections without needles?

I remember very severe warnings being given for handling the fuel injectors on diesel engines. It's not because they are sharp, it's because if they operate when you are handling them, the can emit a jet of high pressure diesel that can go right through the skin and kill you from diesel poisoning. People regularly die from careless handling of them.
17. ## Is it possible for some creatures to experience time faster or slower?

Time obviously passes for all creatures at the same rate. However, they do "experience" it differently. Just like they experience distance differently. An ant will experience two metres differently to an elephant. For the elephant it's just one footstep. For the ant it's several hundred body lengths. We all experience the same thing in different ways. One thing we have in common though, is the length of the day and night. And winter and summer. But our experience of those things we have in common is also different. In general it comes down to scale. Big things experience size and time differently to small things. Size and time are common to all, but how we experience them is unique to each.
18. ## Giant kelp farms to save the world!

Probably the pump. You have to extract the iron ore from the Earth, crush it, and transport it to ships, and then sail it to the target. And Iron ore has a market price which you are losing out on. With a pump, you only need to overcome the friction in the pipe. A tiny amount of energy. And you could use wave motion to power the pump.
19. ## Discerning LED white light from natural sunlight?

That's a good spot. I just tried my torches to see if they strobe. (simply waved them fast in front of my face). You can see the on/off clearly. The plain torch with no dimmer setting doesn't strobe. The one with the dimmer doesn't strobe, on full power, but does, on dim. Not something you would notice, unless you were told it, or noticed it in your bicycle wheel. It's a mystery why that one gets warmer, and has poor battery life, whereas the other doesn't. It might just be a poorer design, not related to the dimmer circuits. But it does get warm, even on dim, and even on dim the battery does run down faster. They both use a quality 18650 Lithion cell, they are great batteries, and seem to hold full charge for ever if you don't use them. A huge improvement on NiMh.
20. ## Discerning LED white light from natural sunlight?

Yes of course. That's the stated purpose in the OP, but in the case of the torches, I guess there could be times when you want to dim it for other reasons. I find it pretty easy just to put a finger over the lens, if I want a dimmer light. In the case of torches, I think what would be ideal would be to have an optional selectable low-power LED, rather than some electronics to dim the supplied T6. You would get more battery life that way, than the set-up that's in the dimmable one. The one I have that isn't dimmable has a much longer battery life, on the same batteries. Some LED torches that have multiple LEDs can select different numbers of LEDs to light up, I think that's a better system.
21. ## A new theory of mine. Why sub atomic substances can exists.

It reminds me of the problem of finding out if someone is realy asleep, or just resting. You can't find out, without giving them a nudge.
22. ## Discerning LED white light from natural sunlight?

You need to be careful when buying dimmable systems. If the objective is to save energy, you may be wasting your time on dimmable ones, because the electronics involved in dimming them might be just dumping the extra energy as heat. I have a couple of LED torches that work on batteries. One is dimmable and the other is not. They both have the same Cree T6 LED and both are very good and bright. But the dimmable one gets warm, even when dimmed, and the battery actually doesn't last as well as the non-dimmable one, even if it's on the lowest brightness setting. Clearly, the reason that it gets warm in the hand is because the electronics are dumping some power as heat, in order to make the thing dimmable. It doesn't really affect the use of it, but it's ironic that the non-dimmable one on full power lasts longer on it's battery, than the other on the dimmest setting. It defeats the object of having dimmable lights.
23. ## Can plants get "fat"?

Another factor in plants storing easy-to-access energy reserves, is that it would attract attention from plant-eating animals. It could well be self-defeating, to make yourself an attractive meal, when you can't run away from the animals that would like to eat you. If you evolve an energy store, some animal is going to evolve a way to eat it, and you end up worse off. The plant would have to evolve successful defence mechanisms, along with evolving the store.
24. ## An improvement on Redshift?

I don't think that would affect it, because what you are measuring is the velocity of your clock. I think that the doppler shift would affect all of your readings equally, so it wouldn't change which reading gave the minimum value for T. Since your various clock readings can be in varying directions as well as various speeds, the clock that gives the smallest value for T should give direction as well as speed. Edit: not so sure having thought about that. Maybe you could compensate for doppler, if you already have a value for redshift?
25. ## Physics Question Related Pressure

If the bag was sealed at sea level, it then contained a fixed volume of air, once it's sealed. As you climb the mountain, the outside pressure drops, and so will the pressure in the bag, if it's not tightly packed. With the drop in pressure inside the bag, the gas inside will expand. As you climb, the air inside the bag will keep expanding, as the pressure keeps dropping. Once the bag becomes tight, the tightness of the bag prevents the air inside the bag from expanding any more. So then you have a pressure difference between the inside and the outside of the bag, so the bag will become fully tight, like a balloon, and will keep the gas inside under higher pressure than the outside air. The temperature outside will play a part. It will cool the gas in the bag, and work AGAINST it's expansion. But if the bag expands, then the pressure effect has outweighed the cooling effect.
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