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

Before you read this, it might be useful to read post 16.7. The most common way to measure angles is to divide a complete revolution (for example, of a wheel) into 360 degrees, usually written as 360o. Then a right-angle is a quarter of a revolution, 360o/4 = 90o. Another way is to divide a… Continue reading 17.11 Measuring angles

Before you read this, I suggest you read post 16.50. Let’s suppose we want to use the (grey) spanner to loosen the (red) nut, in the picture above. We apply a force, F, that makes an angle θ with the axis of the spanner at a distance L from the axis around which the nut… Continue reading 17.10 Torque – using a spanner

Have you ever read the phrase, “Scientists believe that…”, or has anyone ever said it to you? What does it mean? I think it means that something is supposed to be too difficult for you to understand but somebody in authority believes it – so you ought to believe it too! Fortunately, science doesn’t work… Continue reading 17.9 Scientists believe that…

Before you read this, I suggest you read posts 17.6 and 17.7 A cruise ship has a mass of about 5 ×107 kg. (This is usually called the tonnage of the ship and is usually measured in US tons or metric tonnes). How can this be measured? First notice that part of a floating ship… Continue reading 17.8 Weighing a ship

Before you read this, I suggest you read posts 16.44 and 17.6. Suppose you are asked to find out whether a gold ring is made of solid gold or a cheaper metal with a gold coating. You need to do this without damaging the ring. How are you going to do it? The simplest way… Continue reading 17.7 Solid gold?

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