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Saturday, January 30, 2016

Energy resources

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Energy resources are the things we use to make our electricity. They all in involve changing another type of energy into electrical energy.
Currently we mainly rely on fossil fuels, coal, oil and gas. These fuels are called fossil fuels as they have been formed out of the fossilized remains of plants and sea creatures over millions of years. We use them by burning them to heat water into steam. This steam is shot at a turbine and the turbine spins the generator which puts out electricity (remember when water changes to steam it expands 1600 times which give s the force required to spin big turbines). There are 3 problems with using the fossil fuels.
1. Firstly they will run out. We are using them much faster than they are replaced.
2. Acid rain burning coal in particular produces sulphur dioxide which dissolves into the rain making it acidic. When this rain falls it pollutes rivers, lakes and the soil this kills fish and stops trees taking in water which kills them too. The acid rain can also erode buildings.
3. Global warming. Carbon dioxide is also released when you burn fossil fuels. The molecules of this absorbed heat passing through the atmosphere which would usually escape to space and so the temperature of the planet increases. this will lead to melting ice caps, sea level rise (mainly caused by the water in the sea expanding) which will lead to flooding and extream weather as there is more energy in the atmosphere.
So we need to look at alternatives. See the next post for these.

Wednesday, January 27, 2016


Density measures the mass of cubic centimetre of a material.  This is an important physical measurement for designers, scientists and engineers.  For instance the density of iron is around 7.8 g/cm3 (so a cube one centimetre in all three directions has a mass of 7.8 grams) but the density of Aluminium is only 2.7 g/cm3.  If you replaced all the aluminium parts of an aeroplane with iron it would not get off the ground because the mass of each part would be around three times higher.
Density is also important in predicting if things will float.  A material will float if it is less dense that the liquid or gas it is in.  Water has a density of around 1 g/cm3 (well exactly 1 g/cm3 at 4 degrees centigrade) so materials with a density of less than 1 g/cm3 will float but those with a density of more than 1g/cm3 will sink.  This is also why Helium balloons float, they are less dense than air.
 If you put a helium balloon into a room full of hydrogen what would it do? Well it would sink. Helium is more dense than hydrogen.
Heating and cooling things can change their density.  Hot air balloons work by this principle heating the gases of the air gives the particles more energy so they move apart.  This means there are fewer of them in the same volume of space so compared to the cold air outside the balloon the density drops and the balloon starts to rise.  This is also how convection cells or current work.  Cooling most things makes them smaller so their density rises.  This does not happen with water!  When water freezes it expands and so its density actually goes down which is why icebergs float.
To work out the density of a material  we need to know how to find it mass and volume.  There are different ways to do that shown on these videos:  Density of a rectangular solid<>,  Density of a liquid<>, Density of an irregular solid<>

Monday, January 25, 2016

Energy types

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When anything happens around us it involves energy being changed from one type to another. This could be you talking, the electricity going into your computer to light up the screen, a log burning on a fire or a weight bouncing up and down on a spring.
Its important to remember the law of conservation of energy.  This is that we can not make energy, or destroy it, but only change it from one type to another.  The key types of energy you need to know are:
Gravitational Potential energy, (gained when lifting object up, for example being lifted on a ski lift)
Elastic potential energy, (stored in things that are stretched, for example in a catupult which has been stretched)
Chemical energy, (stored in materials and released in chemical reactions for example in your food, magnesium about to be burnt or an electrical cell)
Kinetic energy,(the energy of moving things, like a moving car)
Electrical energy  (the energy carried by a current, through the wires in your computer)
Thermal energy (heat energy nearly anywhere!)
Sound energy (the energy released by things vibrating, like a guitar string)
Light energy (the energy carried in electromagnetic waves some of which we can see, from example from a torch or the Ultra Violet rays that burn us when we forget sun cream.)
The first three are all potential energies.  They can be stored and have the potential to be released at any time.
So an battery powered torch stores chemical energy in the cell.  This is moved as electrical energy as the current flows through the wires and is released as heat and light from the bulb (see this video).  So in the torch the light is the useful energy and the heat is wasted.
Or in a fire the chemical energy stored in a log is again released as heat and light, as happens when any fuel is burnt.
The amount of energy involved in these changes can be estimated quite easily.  If a fly crashes into you the feeling is very different if a rugby tackle is made on you at the same speed.  So the mass of the object makes a big difference.  If the rugby tackle happens slowly it is very different to one at full speed, and so on.  We measure the amount of energy in Joules (but of course still use calories as well when we think about the energy in food).