Before you read this, I suggest you read post 20.7. For security reasons, there is a limit to the quantity of gels you can take on to an aeroplane. But do the passengers or security staff understand what a gel is? And what do the people responsible for the rules mean by the word “gel”?… Continue reading 20.39 Gels

Before you read this, I suggest you read post 20.32. In the English language the word “sugar” is often used to mean “sucrose” – the sugar extracted from sugar cane or sugar beet that is often used to sweeten foods and drinks. But sucrose is not the only type of sugar – other examples are… Continue reading 20.38 Sugars

Before you read this, I suggest you read posts 20.34 and 20.36. Poiseuille’s equation (highlighted in yellow above) enables us to calculate the rate of flow, R (volume divided by time), of a liquid of viscosity Ƞ in a narrow horizontal tube of radius a and length L, when there is a pressure difference, Δp,… Continue reading 20.37 Poiseuille’s equation

Before you read this, I suggest you read posts 17.15, 20.34 and 20.35. The equation highlighted in yellow, above, is the Navier-Stokes equation for incompressible flow of a fluid. A more complicated form of this equation can be used to explain the flow of compressible fluids. For more information on incompressible and compressible flow, see… Continue reading 20.36 The Navier-Stokes equation

In post 17.15, we saw how fluid flow could be explained by two equations – Bernoulli’s equation (conservation of mechanical energy) and a continuity equation (conservation of mass). But, conservation of mechanical energy assumes that the viscosity of the fluid is negligible because viscosity dissipates mechanical energy (post 17.17) and so is similar to friction… Continue reading 20.35 Incompressible and compressible fluid flow

Before you read this post, you should understand the dot product of vectors (appendix 2 post 17.13), the cross product of vectors (post 17.37) and partial differentiation (post 19.11). I have been asked to write a post on the Navier-Stokes equation that was briefly introduced in post 17.15. Before I write it, I need to… Continue reading 20.34 The operator ∇

I have written this post to help students who are studying mechanics. My blog is recommended as a source of information to first-year undergraduate students studying mechanics at a UK university. Unfortunately, they have found it difficult to relate the structure of the blog to the list of topics in a conventional mechanics course. So… Continue reading 20.33 Using this blog to study mechanics

Before you read this, I suggest you read post 16.30. In post 20.27 we met optical isomers – molecules that have thee same atoms joined to each other but are not identical to their mirror images. Isomerism is the existence of different molecules with the same chemical formula; the different molecules are called isomers. Isomerism… Continue reading 20.32 Isomerism

The picture shows a line of length a and another line of length b that are joined to make a line of length a + b. Note that a is longer than b. Now if a/b = (a + b)/a the result is called the golden ratio, φ. It has other names: for example, the… Continue reading 20.31 The golden ratio

Before you read this, I suggest you read post 20.27. The picture above shows a molecule of tartaric acid. This molecule is chiral – it is not identical to its mirror image (post 20.27). The form of tartaric acid shown in the picture is called D tartaric acid; its mirror image is called L tartaric… Continue reading 20.30 Diastereoisomers