studiot

Exactly. And the Earth has a definite dimensions, volume etc. But these are so small compared to the size of the orbit that when we consider the property of position - "where is the Earth ?" - we ignore these and consider a point in space.

That short article is the basis of it. +1 Do you want more ?

I still don't see any answer to my question. What exactly do you see and the conundrum itself, given that all agree the transit times of the horizontal and diagonal beams are different ?

Why ? Particles are not points. Strictly when we model them as points we should use the term point particle to indicate that The property of that particle we are interested in can be considered to act at a point for our purposes. For instance in relation to its orbit around the Sun, the Earth can be considered as a point particle because its size is minute compared to the size of the orbit. If the above condition is not met then we usually call a particle a body or a free body.

An admirable summary of the most important points about the nature and source of heat, including the often missed point about transfer being dependent upon transfer difference. +1 I would just like to add one further often missed point, about radiation. Conduction and convection are well enough described by molecules jiggling about. But where does radiation fit in - there are no molecules carrying it ? Well where there are molecules in motion there are also electrons in motion. Electrons are charged particles in local EM fields and such charged particles in motion emit photonic radiation,

Firstly you don't actually need a router you need a switch most folks cant tell the difference, but switches are cheaper and better for your purposes. I assume you already have a router in your house internet ? So if you have a spare ethernet connector in the back of your incoming internet then you would connect a PoE switch to it and take the output of the switch 100m to a repeater This would then boost the signal for the next 100m and finally end up in another switch at the cabin. A second switch there is a good idea as it would allow for future expansion. The used to do 2 port switches but the main makes seem only have 5 port these days - I will keep looking There is PoE and PoE + which gives greater electrical power. Another way to reach 300+m is to use fibre. This and PoE repeaters (extenders) are discussed here https://intellinetsolutions.com/pages/poe-extenders-repeaters

PoE, thanks. +1 But there are wiring considerations so Dim if you are thinking of this please ask for more details. You do not wnat to try to connect PoE equipment to non PoE equipment since you are diverting some of the wires in the cable from signal to power. Wall jacks are good, (and easier to wire up than plugs), but the danger is that someone will try to conneect something with an ethernet socket to it someday eg a TV or expensive radio or just a common or garden PC. Most devices are use the non powered standard and will suffer if connect to a DC voltage.

Why ? A small ball bearing will do more damage to a large billiard ball than another large billiard ball if one hits the other at speed. If the striking object is large enough it may simply knock the planet to a new orbit, more than damage it. Before someone jumps in, this is not to say there will not be any damage.

Thanks, yes good value today as things have gone up, I expect I paid less than that but I only had a quick look around. The thing is that cable is outdoor grade as well. Cat5E is the original very fast ethernet standard. Cat6 is even better, but harder to work with. Cat = category. Can you put plugs on the cable ends yourself or get someone to do this ? Pre-terminated (plugs on) cables are available up to 350 metres, but they are expensive. Dim, You didn't answer my question about power, is your light going out ? ..which still needs an external power source i.e. a wire or powerbank, a solar powerbank, or a solar panel alone.. Not necessarily. There are spare pairs in the cable that can carry power from either or both ends. I wired up quite a few distribution networks in large buildings (hotels) like this. The term for this is cable powered router.

The problem with showing a moving version is that t would take different amounts of time for the straight and the slanted beams to reach the end of the car, OK you have outlined what you see as the problem viz that a horizontal beam takes a different time from a diagonal beam to reach the front of the train. What you have yet to tell us is exactly what your reasoning is to arrive at the conclusion that this amounts to a conundrum. ? So please explain with your working. Just pulling figures out of your hat is not enough. Show your working. As to your dismissive second paragraph. I will remain polite and hust point out the for the last century Astronomers have been doing exactly this to correctly place the stars in the sky. An absolutely vital exercise.

The snapshot is instantaneous (i.e. the diagram is correct) from the ground's perspective. Snapshots don't move. The train passes the ground observer while the light beam approaches the front of the car from behind. Earlier in you reply to Otto you offer an abstract deduction in reply to his abstract deduction. A snapshot in my view is different since it implies observing all the light reaching one point (the ground observer) at one time, as with any photograph. This of course must take into account the difference in transit tiem of the light from each end and the middle of the train. You see the same effect when drawing diagrams of spaceships outward and return journeys sending time markers every hour, day, whatever in their time, but arriving non linearly at the base observer.

Thank you for reminding me of that thread. Here are a couple of references from that thread (my highlighting) Do they sound familiar?

That is a confusing way to look at it because your 'snapshot' is far from instantaneous. The snapshot is 5m wide in the frame of the ground observer. And tkes times to pass.

So you managed to confuse even yourself. Diagrams themselves however are always good to have. What about addressing swansont's excellent point about direction ?

Noted and accepted, but I will offer comment on some of your points. No, I am not Scottish, though my Welsh grandmother was fond of claiming roots in all four UK countries. In those days there was no prebirth gender determination so few folks wasted money on inappropriate preparations, and bought white baby clothes. Baby showers were an american invention not popular in the UK. Hand-me-downs from the extended family were also more popular in those straitened times. It has also been interesting how those junior relatives have grown up and fared. They could not be more different, but I put the difference down to being different people, not different gender. One last comment about Nature and Nurture. There is an inherited heart weakness in their family, affecting at least as far back as great-grandfather, grandfather, father and my cousin but not the girls it seems. This weakness has certainly conditioned life responses and choices down the line.

Well this somebody is even more confused by what you are trying to say than before. What you say now seems to confirm what I thought you said in your opening paragraph in your opening post, and I agree with that. What follows in both posts is what is confusing since you now seem to have introduced new terminology which to me is even more muddled than before. Please explain again what you think is happening the problem is, using only one name or better symbol) for each variable. Where did this 'conundrum' come from ? Can you give a reference or did you think it up yourself ?

Love this comment. I remember being set to watch my much younger infant male cousin a time or two. He was definitely in that age group. And he spent most of the time I was watching crawling around chewing the table and chir legs (no he did not pick them up). Interestingly when his sister came along a couple of years later I never saw her do this and I was told she didn't. Personally I blame the family corgi setting a bad exmple. Perhaps the lad identified himeself as a corgi.

I repeat swansont's comment from your previous thread. You seem to be mixing frames up. Who are the 'we' at the bginning of paragraph 2 ? You have specified a square train. What shape do you think it is in the 'stationary' frame ? Please clarify your description before you confuse everybody.

Quite Frankly, Tom, there are plenty of other members that are more rewarding to talk to than you are so my focus of attention has shifted away from yourself.

Why Plenty available in the kitchen cupboard to start with. The see what the local pharmacy will let you but. Potassium permanganate is a good on, but take care it is very staining. Form the kitchen you can get near pure Sodium Chloride Sodium Bicarbonate Acetic Acid (get the clear vinegar) Starch Iodine Sugar That's a good start and spread. More dangerous stuff from the household cupboard Hydrochloric acid (descaler) Sulphuric acid (car batteries) Bleach (sodium hyochlorite) So you will be able to learn about and experiment with acid/alkali reactions, redox reactions, salts, colour changes and their analytical uses, effects of temperature and much more. What heat source are you thinking of ? You can get small spirit lamps which are good for beginners. Test tubes and a rack - larger reaction vessels need more ingredients. Glass rod yes good thinking about the safety glasses and other clothing +1 I'm sure there are some good books and websites for beginners at home, also ask your teacher. There are some great electrochem experiments on youtube as well

You can get 300+ metres of Cat5E or Cat 6 cable for under £50. https://www.ebay.co.uk/itm/263661406588?hash=item3d6371c97c:g:0u8AAOSwRbtaTVBD&amdata=enc%3AAQAHAAAAoAyWySM%2FH%2FeJk0nCK%2BYKHCrzQSPzciD07Og%2BI1zAWi3myz34NXWws5w29bnKSktx2YrRVgC%2BTOg88WNqY9ytcbxNDM73mW3g4AgnVJb%2F%2BT2mKCoA7FOurT9bCGm4JZi6b8Br84eHsg6Vb%2F8gS%2F1AyztYSYVA3i1UPtWTWfNwf%2BVkDkfQeYtFo7gic754NSibCRZljifYeNfhHGoYOEigywY%3D|tkp%3ABk9SR-LOz_jEYQ But ethernet cable is only meant for 100m.max. Beyond this you would need an intermediate signal booster amp eg a router or switch as the cheapest option.

Studiot used to do this alot for Exmoor residents (farms etc). Yes, you could run a telephone line down there but you would require external grade cable. So I have two possibilities to offer. Somewhere in the boxes of kit I still have one pair of narrow beam transmitter/receivers unopened in the boxes. The have a range of slightly over 1km. and were made especially for this sort of application. You are welcome to these for the cost of postage or collection if you ever visit Somerset. I had a quick butchers in the store but couldn't locate them yet. I do know they are there somewhere. Please note these are 'line of sight' only so if your cabin is hidden they won't work. Alternatively you must be running power down there, unless you have a generator. I had a good deal of success with 'through the mains' transmitters with a distributor device at the receiving end. Unfotunately these were always in short supply, so they seemed to go out as fast as I could get hold of them, so I have none left.

How many folks died in the Grenfell disaster because of this mantra ? Anyway this thread is about electric foil heating systems. And the outside temperature was stated as -2C in the article. It was also stated that the system would 'not cost less to run'. Please keep on topic.

Learn a little bit of theory and a lot of safety. Practical Chemistry can be fun, but can also be dangerous. Chemists don't 'make' elements, they make compounds, which are substances that are combinations of 'elements'. To start with don't worry about atoms, molecules and electrons. Start with the idea that 'elements' are substances that cannot be divided or separated into anything simpler. There are a little over 100 naturally occurring elements. A simple example is a lump of pure carbon. If you keep dividing and subdividing ths lump you will always have pieces carbon and nothing else. Chemistry is mostly about two things, how to combine these elements into compounds and how to separate out pure elements from compounds and mixtures. There are many, many ways to perform both of these tasks. But hydrogen separation can be dangerous as hydrogen gas is potentially explosive. Does this help ?

Beware these materials https://sourceable.net/expanded-polystyrene-is-just-as-deadly-as-acp-cladding-in-a-fire/