Falling trees in secluded areas and stuff like that... Sound.

As in the sound we hear. Not the common slang expression to express your acceptance.

Sound waves are longitudinal (waves in which particles oscillate along lines in the direction in which the wave travels,) waves produced by variations in air pressure. The wave is a mechanical wave, as it requires a medium in which to occur. Thus, in a vacuum where there is nothing, sound can not travel.

Sound is made by a vibrating source which moves the molecules in air, creating areas of compression and rarefaction. When a molecule moves, it collides with the next one and thus also makes it move. The energy of a sound wave travels away from the source through the series of collisions parallel to the direction of the wave.

Rarefaction is the reduction of a medium's density, or the opposite of compression. Half of a sound wave is made up of the compression of the medium, and the other half is the decompression or rarefaction of the medium.

Sound travels faster through denser materials because a higher density leads to more elasticity in the medium and increases the ease by which compression and rarefaction can take place.

What's that smell? Uhhh... Ammonia!

At least it's not butanoic acid... Uhhh... I recently had a nasty run in with that!

The Haber process is a reaction of nitrogen and hydrogen gasses, to produce ammonia. Before the advent of the Haber process, ammonia was difficult to produce on an industrial scale, though used in fertilisers and munitions. (YAY for feeding people, then shooting them...) Despite the heavy content of nitrogen in the air, it is a not very reactive gas, due to the strong triple bonds that hold the molecules together.

The process was developed in 1909, by a German scientist, called Fritz Haber. (Hasn't he some awesome spectacles?)

The equation:

N2 (g) + 3 H2 (g) <-> 2 NH3 (g)

(To my frustration, Blogger won't let me use an equilibrium sign.)

The gasses, a are passed over an iron catalyst and are heated to about 300 degrees centigrade with typically only a 15% conversion rate. This is repeated several times (recycled) so that an overall conversion of 98% can be achieved. The equation is an equilibrium reaction, so ammonia is at the same time converted back to nitrogen and hydrogen. Because of this, the process takes place under certain conditions to ensure the maximum of the desired product. I would explain more, but it would take a long time, and I'd probably bore you.

You what Archimedes?

You are supposed to have run through the streets of Syracuse naked when you discovered upthrust? Nice.

Saying that, I do like upthrust. It stops you from drowning and instead makes you float. The principal goes;

'When a body is totally or partially immersed in a fluid, it experiences an up thrust equal to the mass of fluid displaced'.

Supposedly Archimedes discovered this law while taking a bath. He noticed that the level of the water in the tub rose as he got in, and realized that this effect could be used to determine the volume of the object.

Water is assumed to be incompressible, so the submerged object would displace an amount of water equal to its own volume.

He then found that by dividing the mass of the object by the volume of water displaced, the density of object could be found.

He is said to have used this idea to prove that a crown was made of lesser materials, rather than gold, as he showed the crown to be less dense.

ZZAP! If this wasn't a semiconductor this shock would have frazzled my mind...

A semiconductor is a material that behaves in between a conductor and an insulator. At room temperature, it conducts electricity more easily than an insulator, but not as well as a conductor.  At very low temperatures, semiconductors behave like insulators. At higher temperatures semiconductors can become conductive. Examples of semiconductors are silicon, germanium, and gallium arsenide.

You can dope semiconductors. Luckily, this is not blasting them off of their faces with liberal amounts of drugs, it is the process of adding impurities to a semiconductor to increase its ability to conduct electricity. These combined with a normal semiconductor can make diodes - components in a circuit that conduct electricity in only one direction.

Semiconductors also make transistors - used to amplify and switch electric signals. They are used very commonly - in most electronic goods including computers. Circuit boards make heavy use of semiconductors.

Yay for Slow Moving Spheres!

­­­­Let me tell you a story, boys and girls, about one Sir George Stokes.

He came up with a mathematical description of the reactionary force that works against a sphere moving through an inactive, viscous fluid at a low velocity. (Very exciting, I know.)

His law; Stokes' Law is written as: Fd = 6πμrv

• Fd is the drag force of the fluid on a sphere.
• μ is the fluids viscosity.
• v is the velocity of the sphere.
• r is the radius of the sphere

While Stokes’ Law is straight forward, it is subject to some limitations. Specifically, this relationship is valid only for laminar flow. Laminar flow is defined as a condition where fluid particles move along in smooth paths in fluid layers gliding over one another. This means his expression only works for as the title states; for slow moving spheres, as a fast object would not travel with laminar flow and a sphere is only relevant as the expression requires a radius.

What I'm trying to say is it's not very relevant in most situations. Luckily, good old Stokes is better known for other works. (Why I did not cover them, I do not know!)

Why does the sound of emergency sirens change as you pass them by?

This effect is called Doppler Shift. What does that mean, you ask. Well...

When the source of the waves, in this case the siren, is moving toward the observer, each successive wave is emitted from closer to the observer than the previous wave. Each wave takes less time to reach the observer than the previous wave and thus the time between the arrivals of successive wave crests are reduced, causing an increase in the frequency.

If the source of waves is moving away from the observer, each wave is emitted farther from the observer than the previous wave, so the arrival time between each wave is increased, reducing the frequency.

This is also the case when a car passes you by; you get a higher pitch on the approach, followed by a lower pitch noise as it has passed you by.

It sounds like (taking a deep breath for childish noise time...) NEEEEEEEVVVOOOOOOOOOOMMMM

Light can be bent... (Sort of.)

Diffraction is the bending of waves around an object in its path. This is due to how it spreads out from the source, not in straight lines, but in curved waves. Light is a wave, so in effect it does bend.

When waves reach a narrow slit, the wave in the slit vibrates like a point source. The waves thus sent out from secondary sources along the slit are nearly in-phase when arriving any point in the forward direction. The diffracted wave resembles a circularwave with centre at the slit.

The amount of diffraction depends on the wavelength and the size of the object that the wave hits. Waves with a larger wavelength diffract more, and smaller wavelegnths diffract less.

An example of this is your shadow. Shadows aren't sharp images; they are fuzzy around the edges, which is due to diffraction. As the rays hit you, the waves bend around you and then continue on, but they have been changed, and so the image projected on the ground is no longer sharp.

Sound also travels around corners because of it. Lower frequency sound waves diffract better.Light does not diffract well, as it has a very small wavelength, and is thus why we cannot see around corners. (It still can, just only a bit.)