Theoretical Study of Air Pressure

My group choose Air Pressure for our theoretical study.

Air pressure is the force exerted (applied is simpler)by the weight of a column of air above a particular location. the exemple of air pressure are drinking with the straw and injection. Air pressure has relate between science and technology, the example of daily life are plane with our life modern to go another country easily, and then syringe in the modern of medicine. and this is our experiment to complete the theoritical study about air pressure. when A flame goes out inside of an upside down jar and, like magic, the jar is stuck to a plate. You might think that the jar has sucked right to the plate, but we’ll explain why this trick is actually a result of pushing! The Stuck Like Glue experiment is an incredible demonstration of the power of air pressure and a great way to help explain the way that forces work.

   if you have to watch the video, maybe you are feeling curious now, how does it work? okey i will explain it more than on video. 

    

   When the piece of paper inside of the overturned jar is lit, the air inside the jar is heated, causing it to expand. When the flaming paper is extinguished, the air inside the jar cools and contracts, leaving a void of air within the jar. This is an example of an imperfect vacuum. When you think of a vacuum, you think of suction, but scientists like to avoid the term "suck," and instead rely on the pushing forces from outside. With the vacuum inside the jar, air from outside really wants to get inside. Were it not for the wet paper towel, the outside air would succeed and the vacuum would be no more. However, the water in the paper towel effectively stops the air from rushing back into the jar. Water (as well as other substances) has two properties called adhesion and cohesion. Adhesion is water's ability to stick to other materials, and cohesion is, you guessed it, water's ability to stick to itself. When the flaming paper is extinguished and you add pressure onto the jar, the adhesion and cohesion of the water create an air-tight seal between the plate, paper towel, jar, and water.This air-tight seal means that air is constantly trying to push its way up and into the jar without success. The air pushing at the seal creates the phenomenon of the plate sticking to the mouth of the jar.

   the related between this experiment with science and technology very wide, maybe we can choose one example that the work is near with this experiment, for example Cupping technology in medicine. Cupping and this experiment has a lil bit same materials and 'how does it work'. i will emphasize about science and technology here. since Cupping has been found, i am sure that it is happen cause a modern and technology, because science is come from nature and human's brain. and technology is the application of the science. 

left: the experiment || right: cupping

   by the way, talking about air pressure, i remember that air pressure has a related with bernoulli's principle.

Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease inpressure or a decrease in the fluid's potential energy. Bernoulli's principle is named after the Swiss scientist Daniel Bernoulli who published his principle in his book Hydrodynamica in 1738.

Daniel Bernoulli

Bernoulli's principle can be applied to various types of fluid flow, resulting in what is loosely denoted as Bernoulli's equation. In fact, there are different forms of the Bernoulli equation for different types of flow. The simple form of Bernoulli's principle is valid for incompressible flows (e.g. most liquid flows) and also for compressible flows (e.g. gases) moving at low Mach numbers (usually less than 0.3). More advanced forms may in some cases be applied to compressible flows at higher Mach numbers (see the derivations of the Bernoulli equation).

Bernoulli's principle can be derived from the principle of conservation of energy. This states that, in a steady flow, the sum of all forms of mechanical energy in a fluid along a streamline is the same at all points on that streamline. This requires that the sum of kinetic energy and potential energy remain constant. Thus an increase in the speed of the fluid occurs proportionately with an increase in both its dynamic pressure and kinetic energy, and a decrease in its static pressure and potential energy. If the fluid is flowing out of a reservoir, the sum of all forms of energy is the same on all streamlines because in a reservoir the energy per unit volume (the sum of pressure and gravitational potential ρ g h) is the same everywhere.

Bernoulli's principle can also be derived directly from Newton's 2nd law. If a small volume of fluid is flowing horizontally from a region of high pressure to a region of low pressure, then there is more pressure behind than in front. This gives a net force on the volume, accelerating it along the streamline.

Fluid particles are subject only to pressure and their own weight. If a fluid is flowing horizontally and along a section of a streamline, where the speed increases it can only be because the fluid on that section has moved from a region of higher pressure to a region of lower pressure; and if its speed decreases, it can only be because it has moved from a region of lower pressure to a region of higher pressure. Consequently, within a fluid flowing horizontally, the highest speed occurs where the pressure is lowest, and the lowest speed occurs where the pressure is highest.

 sources: 

http://en.wikipedia.org/wiki/Bernoulli's_principle

http://www-history.mcs.st-andrews.ac.uk/PictDisplay/Bernoulli_Daniel.html

Stuck Like Glue - Air Pressure Trick at Steve Spangler Science