Material halts liquid flow on demand http://www.bbc.co.uk/news/science-environment-22079600
Category Archive: AQA Unit 2 Forces/ Motion/ Waves
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A common problem for teaching Physics when you are not a Physics teacher is that you make many mistakes with complex ideas which appear simple on the surface.
I drop a ball to the earth and want to work out the distance fallen in a certain time. I then do a calculation of..
distance x speed = time
Oh dear but when I do the experiment it does not work like that but it works like this…
Now we can reason this out. If I allow a ball to fall to earth it must accelerate due to the field of gravity around the earth 9.81N/kg. Or 9.81 m/s/s.
But where does the formulae come from that we general use?
This post is simply to give some advice about this formulae. To start with define everything we use…
- s = the distance between initial and final positions (displacement) (sometimes denoted as x)
- u = the initial velocity (speed in a given direction)
- v = the final velocity
- a = the constant acceleration
- t = the time taken to move from the initial state to the final state
So the question is what is it all about.
Well we need to think way back to the idea of a simple idea of how to work out the distance travelled by a runner in a race.
Think of an athlete travelling 100m in 10s at a constant speed. His velocity or speed is…
Now this works fine if we are travelling at a constant speed but hey as you know this is not always the case and sometimes an object has a constant acceleration or deceleration. If you think about a graph of a person who got faster and faster then we would have a slope or triangular area on a speed-time or velocity-time graph. Now the area under the graph would be the distance travelled on the journey. But if our speed changed s=vt (for constant speed) becomes….
Now you have an expression for the average speed but only from a standing start. Imagine now the same velocity time graph but this time the runner was already travelling at a velocity at the start of timing. Our area would become a triangle and rectangle…
– Eq 2
This is the formulae for average speed that takes care of all situations even when u or v is 0. Now then think graphically again if we are travelling at an initial velocity and then accelerate we are back to triangle and square again when looking at a vt graph. Hence…
– Eq 1
Now we can use this in a rearranged form..
Substitute into Eq 1 in new form into 1 to remove t so we now have an expression…
Which simplifies to..
– Equ 4
Now we have this we can work also work backwards to get Eq 3 …
– Eq 1
And *t gives..
Divide both sides by two…
Add ut to both sides, multiply by 2 and tidy up..
– Eq 3
So we now have the four equations of motion for an object which is travelling at a constant velocity or accelerating at a constant rate. As shown you can reason them all out with very simple ideas from first principals. You can also call them whatever number you want as some people label them differently.
So hopfully we have now understood where the formulae comes from and realise that if we drop a ball we must apply the formulae to work out the distance fallen in a more complex way.
Then it gets really interesting when you think about a tanker travelling at a constant velocity which then slows down. How far does it travel as it slows…
Of course, it will be ut for the whole time and then you take away a little bit of “s” from the other term as you slow.
Permanent link to this article: http://www.animatedscience.co.uk/2011/equations-of-motion
In the prototype, sunlight heats a ceria cylinder which breaks down water or carbon dioxide
The machine uses the Sun’s rays and a metal oxide called ceria to break down carbon dioxide or water into fuels which can be stored and transported.
Conventional photovoltaic panels must use the electricity they generate in situ, and cannot deliver power at night.
The prototype, which was devised by researchers in the US and Switzerland, uses a quartz window and cavity to concentrate sunlight into a cylinder lined with cerium oxide, also known as ceria.
Ceria has a natural propensity to exhale oxygen as it heats up and inhale it as it cools down.
If as in the prototype, carbon dioxide and/or water are pumped into the vessel, the ceria will rapidly strip the oxygen from them as it cools, creating hydrogen and/or carbon monoxide.
Hydrogen produced could be used to fuel hydrogen fuel cells in cars, for example, while a combination of hydrogen and carbon monoxide can be used to create “syngas” for fuel.
It is this harnessing of ceria’s properties in the solar reactor which represents the major breakthrough, say the inventors of the device. They also say the metal is readily available, being the most abundant of the “rare-earth” metals.
Methane can be produced using the same machine, they say. Refinements needed The prototype is grossly inefficient, the fuel created harnessing only between 0.7% and 0.8% of the solar energy taken into the vessel. Most of the energy is lost through heat loss through the reactor’s wall or through the re-radiation of sunlight back through the device’s aperture. But the researchers are confident that efficiency rates of up to 19% can be achieved through better insulation and smaller apertures. Such efficiency rates, they say, could make for a viable commercial device. “The chemistry of the material is really well suited to this process,” says Professor Sossina Haile of the California Institute of Technology (Caltech). “This is the first demonstration of doing the full shebang, running it under (light) photons in a reactor.”
She says the reactor could be used to create transportation fuels or be adopted in large-scale energy plants, where solar-sourced power could be available throughout the day and night. However, she admits the fate of this and other devices in development is tied to whether states adopt a low-carbon policy. “It’s very much tied to policy. If we had a carbon policy, something like this would move forward a lot more quickly,” she told the BBC. It has been suggested that the device mimics plants, which also use carbon dioxide, water and sunlight to create energy as part of the process of photosynthesis. But Professor Haile thinks the analogy is over-simplistic.
“Yes, the reactor takes in sunlight, we take in carbon dioxide and water and we produce a chemical compound, so in the most generic sense there are these similarities, but I think that’s pretty much where the analogy ends.”
Daniel Davies, chief technology officer at the British photovoltaic company Solar Century, said the research was “very exciting”.
“I guess the question is where you locate it – would you put your solar collector on a roof or would it be better off as a big industrial concern in the Sahara and then shipping the liquid fuel?” he said.
Solar technology is moving forward apace but the overriding challenges remain ones of efficiency, economy and storage.
New-generation “solar tower” plants have been built in Spain and the United States which use an array of mirrors to concentrate sunlight onto tower-mounted receivers which drive steam turbines.
A new Spanish project will use molten salts to store heat from the Sun for up to 15 hours, so that the plant could potentially operate through the night.
Permanent link to this article: http://www.animatedscience.co.uk/2010/new-solar-fuel-machine-mimics-plant-life