Before you read this post, I suggest that you read posts 16.44 and 17.5. In post 16.44, I wrote that stuff that has a lower density than water will float on water. Why? Let’s think of an object that sinks suspended in water by a thin thread, as shown on the left-hand side of the… Continue reading 17.6 Floating

Before you read this, I suggest you read post 16.44. In post 16.37 we thought about liquids as fluids – things that can flow. But if we have liquid in a container, it doesn’t usually flow. Suppose the container has vertical sides and a cross-sectional area of A. If the column of liquid in the… Continue reading 17.5 Stationary liquids

Before you read this, I suggest that you read posts 16.4, 16.12, 16.13 and 17.2. I walked 2 km, in a straight line, stopped and then walked another 2 km, in a straight line. How far was I from my starting point? All you can tell me is that I was somewhere within a circle… Continue reading 17.4 Displacement, velocity and acceleration

I suggest that you read post 17.2 before this. In post 17.2 we saw how to add two-dimensional vectors – vectors that could be drawn on a sheet of paper. But forces can act in three dimensions – up-and-down, as well as north-south and east-west. A three-dimensional force has the same relationship to a two-dimensional… Continue reading 17.3 Three-dimensional vectors

Before you read this, I suggest you read post 16.50. In post 16.50, we saw that the effect of a force depends on its direction, as well as how big it is – force is a vector. So, if we add a force of 5 N to another force of 5 N, the result can… Continue reading 17.2 Vectors

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