Before you read this, I suggest you read post 21.3. A corkscrew is used to remove corks from a bottle – see the picture above. It is made by bending a metal rod, with a circular cross-section into a shape called a helix. The centroids of all the circular cross-sections lie on a helical line… Continue reading 21.6 The helix

Before you read this, I suggest you read post 21.3. In post 21.3 we met the simple spiral whose equation in polar coordinates is r = aθ                    (1) where a is a constant, r is the radius of the spiral and θ is an angle that is positive for anticlockwise rotation. In this post we… Continue reading 21.5 Logarithmic spirals

Proteins are condensation polymers of amino acids. The structural formula of an amino acid is shown at the top left-hand corner of the picture above, where R is any chemical group. (Two amino acids, proline and hydroxyproline, are slightly different). In post 20.27 we met alanine – the amino acid in which -R is the… Continue reading 21.4 Proteins

I have used polar coordinates in a previous post. But that post contained mathematics that was more much difficult than is needed here. So, I am going to begin with a simple description of polar coordinates. Usually we describe the position of a point in space using Cartesian coordinates; in two dimensions the position of… Continue reading 21.3 Polar coordinates, circles and spirals

DNA is an example of a nucleic acid. Its name is an abbreviation for deoxyribonucleic acid. It was discovered in 1869 by a Swiss doctor called Friedrich Miescher (1844-1895). Most people know that DNA is responsible for coding genetic information but may not know much about its chemical composition, how it codes this information or… Continue reading 21.2 Nucleic acids

While I was compiling the index to this blog, I noticed that I had written several posts about mechanical simple harmonic oscillators but hadn’t written anything about electrical simple harmonic oscillators– the subject of this post. A simple harmonic oscillator is a system that oscillates indefinitely by exchanging potential and kinetic energy. In a real… Continue reading 21.1 An electrical simple harmonic oscillator

Before you read this, I suggest you read post 20.38. Cells (post 16.18) in plants are surrounded by a rigid wall made of the polysaccharide (post 20.38) cellulose that consists of repeating β-D-glucose residues (post 20.38) as shown above. In this picture, the second residue is identical to the first but I have shown it… Continue reading 20.40 Polysaccharides

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