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…