Before you read this, I suggest you read posts 16.20, 17.4 and post 17.19. But if you want to stop at the seventh paragraph, there is no need to read 17.19. In post 16.20, we saw that a force does work when it moves something. This is a simple definition of work and there is… Continue reading 17.36 More about work – line integrals

Before you read this, I suggest you read posts 16.19 and 16.50. The picture above shows the forces acting on an object on a slope – like the vehicle on a road camber in post 17.34. If the object has a mass of m, gravity pulls it towards the centre of the earth with a… Continue reading 17.35 Sliding

Before you read this post, I suggest you read posts 17.13, 17.16 and 17.17. The picture above shows a skier making a right turn by leaning to the right and transferring his/her weight on to the right-hand ski. The pictures above show a motorcyclist turning right by leaning right and a plane turning left by… Continue reading 17.34 Turning corners

William Thomson was one of the most famous physicists of the 19th century. He was born in 1824 and graduated in mathematics, from the University of Cambridge, in 1845. By 1846 he was Professor of Natural Philosophy (the contemporary name for physics) at the University of Glasgow in Scotland. He was made Sir William Thomson… Continue reading 17.33 Lord Kelvin and flying machines

Before you read this, I suggest you read posts 17.16 and 17.31. We often see birds flying without flapping their wings – they are gliding (post 17.31). In order to glide, their wing cross-sections must be shaped so that air moving over the wing has further to travel than air moving under the wing, so… Continue reading 17.32 How do birds fly?

Before you read this, I suggest you read post 17.16. In post 17.16, we saw that a plane flies because, when it moves forward with a speed v, the pressure under the wing is greater than the pressure on top of the wing. The pressure difference, Δp creates an upward force, equal AΔp where A… Continue reading 17.31 Gliding and soaring

Before you read this, I suggest that you read posts 16.13 and 16.21. If I drop a tennis ball on a hard, flat, smooth surface, it bounces back to almost the height it was dropped from. As it drops, it converts potential energy into kinetic energy; after it has bounced, it converts kinetic energy into… Continue reading 17.30 Collisions

Before you read this, I suggest you read post 17.13. In post 17.13, we met the idea of centripetal force – the force that is needed to pull an object to keep it moving round a circle. In post 17.28, we saw how the force exerted by the earth’s gravitational field provides the centripetal force… Continue reading 17.29 Centrifugal force

Before you read this, I suggest you read posts 16.16 and 17.13 Why does a satellite stay in orbit around the earth? If we think of something going round in a circle (like the hammer in post 17. 13 before it is thrown), it appears that something must be pulling it towards the earth. What… Continue reading 17.28 Satellites

Before you read this, I suggest you read posts 17.19, 16.20 and 16.16. But post 17.19, and this one, involve some mathematics that you might wish to ignore – so you may prefer not to read this post after the first few paragraphs! If a rocket is to be launched into space, it must take… Continue reading 17.27 Getting into space