I sometimes read about scientific topics where the writer, often a student, says that something is obvious. Let’s think what “obvious” means. It means that we don’t even need to think about something to know whether it is true or false. I have two objections to using the word when writing about science. My first… Continue reading 17.1 It’s obvious…

Before you read this, I suggest you read post 16.13. In the previous post (post 16.49), we saw the difference between forces that stretch things and forces that act in the opposite direction to compress things. In this post we will think about forces that act in any direction. Let’s suppose we want to use… Continue reading 16.50 Direction of forces

Before you read this, I suggest you read posts 16.13, 16.20 and 16.21. Let’s think about a spring that is fixed at one end; when a force pulls it at the other end, it gets longer. When a spring is pulled, so that it gets longer, we say that it is in tension and the… Continue reading 16.49 Springs

Before you read this, I suggest you read posts 16.45 and 16.47. Why do we use soap to wash ourselves? Why don’t we just use water? If you’ve ever asked yourself these questions, you may have decided that using soap gets us cleaner. So why does soap get us cleaner? Not many people ask themselves… Continue reading 16.48 How does soap work?

The picture above shows how carbon, hydrogen and oxygen molecules combine to form a fat molecule; as expected each carbon atom forms 4 covalent bonds, each hydrogen atom forms 1 covalent bond and each oxygen atom forms 2 covalent bonds. (More information on covalent bonds and molecules is given in post 16.30.) The vertical bonds… Continue reading 16.47 Fats

Has anyone ever recommended something to cure a minor ailment, or something to improve your health, because “it worked for me”? This “something” could be an expensive commercial product (like some dietary supplements), aromatherapy, a copper bracelet, a magnetic bracelet, a change in diet or an exercise regime. The problem is that all of these… Continue reading 16.46 The placebo effect

Before you read this, I suggest you read posts 16.44, 16.30 and 16.27. The density of something is the mass of a sample of it divided by the volume of the sample (post 16.44). So, we might expect that, when we heat a solid, its density will increase; this is because when we heat a… Continue reading 16.45 Water

Which has the greatest mass 1 kg of steel or 1 kg of wood? (If you’re not sure what “mass” means see posts 16.12 and 16.13.) I hope that you immediately realised that both have the same mass of 1 kg. But we all believe that steel is “heavier” (it has a higher mass) than… Continue reading 16.44 Density

It would be useful to read posts 16.8 and 16.42 before you read this. Two previous posts (16.8 and 16.42) were about a biologist who developed a simple model to predict the number of rabbits on a farm. It took him 5 years to collect the data to develop his model. He then used it… Continue reading 16.43 Test before you predict

Before you read this, it would be useful to read post 16.8. Post 16.8 is a story about a biologist who investigated the rabbit population on a farm. He counted the number of rabbits every year for 5 years. When he plotted a graph of the number of rabbits against time, he got a straight… Continue reading 16.42 Keep it simple