If you have been reading and thinking about this blog regularly, you may have noticed that I often ignore the dimensions of an object. For example, when we calculated the speed that a falling object hits the ground (post 17.18), we assumed that the object was a point in space. In this example, assuming that… Continue reading 17.21 Centre of mass

Before you read this, I suggest you read post 17.19. This post illustrates the application of integration to calculate velocity and speed from acceleration, as described in post 17.19. In this post, we will consider an object (like the rock in the picture above) falling close to the surface of the earth, so that the… Continue reading 17.20 Falling

Before you read this post, I suggest you read post 17.4. This post introduces the mathematical concept of integration that makes it much easier to understand many scientific topics. But, if you really don’t like mathematics, you can ignore this post and still understand most parts of most other posts. To keep it simple, I’m… Continue reading 17.19 Calculating distances from speeds – integration

Before you read this, I suggest you read post 17.17. If we ignore viscosity (post 17.17), an object of mass m that falls from a height h, gains a speed of v =√(2gh) (post 16.42), where g is the magnitude of the earth’s gravitational field (post 16.16). This result was derived by assuming all the… Continue reading 17.18 Terminal velocity and parachutes

Try pushing your finger slowly through a glass of water: now try to do the same in a glass of treacle or honey. You will find that the treacle or honey exerts a force (post 16.13), resisting the motion of your finger (rather like friction in post 16.19), that is much greater than the force… Continue reading 17.17 Drag and viscosity

Before you read this, I suggest you read post 17.15. We will think about this question by considering a plane whose wings have the cross-sectional shape shown in the picture below. In this picture, the engines of the plane move it in the direction shown by the arrow. Now let’s think about the movement of… Continue reading 17.16 Why do planes fly?

Before you read this post, I suggest you read post 17.5. A fluid is anything that flows – like a liquid or a gas (post 16.37). In post 17.5, we saw that a fluid remains stationary when there is a surrounding pressure that acts equally in all directions. However, when the pressure is greater in… Continue reading 17.15 Fluid flow

According to the Bible (in the book of Genesis, chapters 9-11), the world was once covered by water, in a great flood. A man called Noah built a big ship (called the “ark”) that he used to rescue his family and all the species of animals. After the flood, his descendants lived in a place… Continue reading 17.14 Confusion

Before you read this, I suggest you read posts 17.12, 17.11, 17.10 and 17.4. The man in the picture is practising “throwing the hammer”. In this event, the participant swings a spherical “hammer” using a cable, as shown in the picture, several times around his/her body. So the hammer goes round in a circle, with… Continue reading 17.13 Centripetal force – throwing the hammer

Before you read this, I suggest you read posts 17.4 and 17.11. In the picture above, the point P is moving in a circular path around the point O. In a time-interval, Δt, it moves from P to P’, and sweeps out an angle Δθ. (In this post the symbol Δ, the Greek letter capital… Continue reading 17.12 Going round in circles