In post 20.20, we anticipated that there must be some relationship between the Young’s modulus, E (post 20.2) and the bulk modulus, B (post 20.20) of a material. The relationship is given by E = 3B(1 – 2ν) (1) where ν is the Poisson’s ratio (post 20.5) of the material. We shouldn’t be surprised by… Continue reading 20.21 Relationship between Young’s modulus and bulk modulus
Before you read this, I suggest you read post 20.2. Let’s think about a solid sphere surrounded by a fluid (post 16.37). If the pressure in the fluid increases, the force on the ball increases because pressure is simply a component of a force divided by an area (post 17.5). We will assume that the… Continue reading 20.20 Deformation of objects – isometric compression
In post 20.2 we saw that forces can change the dimensions of an object; they can also change its shape. Change in shape without changes in dimensions is called shear. The picture above shows a cube ABCDEFGH. Let’s think about what happens when we apply a force f (posts 17.2) perpendicular to the line BF… Continue reading 20.19 Deformation of objects – changes in shape
Before we start to think about this question, we have to recognise that very few scientists are ever really famous. I believe that Charles Darwin, Albert Einstein, Marie Curie, Alan Turing and Stephen Hawking are all names that are recognised by very many people (although there is no picture of Hawking on Pixabay, http://www.pixabay.com ).… Continue reading 20.18 How do scientists become famous?
In post 20.16 we saw how the body was able to control its chemical composition; in this post I am going to write about how it controls its temperature. This post is mostly about temperature control in humans. We need to maintain our bodies at about 37oC to provide the optimum conditions for the chemical… Continue reading 20.17 Homeostasis 2 – controlling the body’s temperature
Before you read this, I suggest you read posts 17.49 and 17.50. In post 20.14, I mentioned the belief that acidic drinks could make our body fluids more acid; similarly, many people believe that eating alkaline foods will make their body fluids less acidic. To find out more about acids and alkalis, and the pH… Continue reading 20.16 Homeostasis 1 – controlling the body’s chemical composition
I suggest that before you read this, you read post 20.14. In post 16.18, we saw that a cell is conventionally considered to be the smallest part of us that is alive. Bone contains four types of cell: osteoblasts, osteoclasts, osteocytes and endosteal cells. In this post we will consider only the first two. Osteoblasts… Continue reading 20.15 Osteoporosis 2 – bone cells
Many people believe two things about osteoporosis that are not true: It makes bones more brittle It is caused by loss of calcium from bones. Osteoporosis makes bones less strong but not more brittle. Osteoporotic bone breaks at a lower stress than normal bone – so it’s less strong. But it does not appear to… Continue reading 20.14 Osteoporosis 1 – bone structure
Before you read this, I suggest you read posts 20.9 and 20.10. In post 20.10 I described toughness as the energy absorbed by a unit volume of material before it fractures. It is often simpler to understand the process of fracture (when something breaks, post 20.10) in terms of energy rather than the stress (or… Continue reading 20.13 Fracture
Like most people, I hadn’t thought much about this topic until the last few weeks. But covid-19 means that every day we see numbers related to the spread of a pandemic. An epidemic has been defined as the “widespread occurrence of infection in a community in a given time”. A pandemic has been defined as… Continue reading 20.12 What happens in a pandemic?