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

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