Posts Tagged ‘fluids’

Dancing Fire!

Posted: January 7, 2012 by Mr Pimentao in Physics, Uncategorized
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Sound seems to have caught the eye here at Loreto’s science cyberspace presence.

Whilst “youtubing” aimlessly like a headless chicken, I came across several videos showing a Ruben tube.

This is a perforated tube connected to a supply of flammable gas on one end, and attached to a speaker on the other end. As the gas flows through the tube holes, the (standing) sound wave created inside the tube by the speaker causes areas of high and low gas pressure. If you fire the gas up, it becomes an impressive flame show. The height of the flame is taller in the areas of higher pressure, so it acts as a visual display of the sound wave that travels inside the tube.

Some people like to play a single note on the speaker and are happy with that. Others experiment with all kinds of sound : from dubstep to glam rock!


Mythbusters playing with Rubens tube

Another one bites the dust on Rubens tube

Bad romance on Rubens tube

Non Newtonian fluids

Posted: January 4, 2012 by Mr Pimentao in Physics
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Many people have heard of Sir Isaac Newton. He is famous for developing many scientific theories in mathematics and physics. Newton described how ‘normal’ liquids or fluids behave, and he observed that they have a constant viscosity (flow). This means that their flow behaviour or viscosity only changes with changes in temperature or pressure. For example, water freezes and turns into a solid at 0˚C and turns into a gas at 100˚C. Within this temperature range, water behaves like a ‘normal’ liquid with constant viscosity.

Typically, liquids take on the shape of the container they are poured into. We call these ‘normal liquids’ Newtonian fluids. But some fluids don’t follow this rule. We call these ‘strange liquids’ non-Newtonian fluids.

The viscosity ( how “runny” a fluid is) of a non-Newtonian fluid depends on things such as the stress, or pressure applied to them. This means that a quick change in the pressure applied to such a fluid might change its viscosity.

Cornflour solution on a speaker cone.

This is the reason that explains the formation of these cornflour “creatures” . Corn starch is a shear thickening non-Newtonian fluid meaning that it becomes more viscous when it is disturbed. The changes in pressure created by the sound vibrations change the viscosity of the fluid, and the result is fantastic. Check it out here.

Another classic example is Mr. Tickle walking on custard.