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

  We have seen that planes fly because air provides “lift” under their wings (post 17.16); any engines that moves the plane forward will enable air to lift the plane. But there is no air in space (because air molecules are attracted to earth by its gravitational field – see post 16.16) so space-craft need… Continue reading 17.26 Rockets

Acceleration is a simple idea – suppose a car increases its speed from 0 to 60 km.h-1 in 3 s. Its final speed is 60/(60 × 60) km.s-1, so its average acceleration is 60/(60 × 60 × 3) = 0.006 km.s-2 (see post 16.13 for more explanation, and post 16.7 if you’re worried because the… Continue reading 17.25 Diminishing deception

Before you read this post, I suggest that you read posts 16.50, 16.25 and 16.16. In posts 16.16 and 16.25, we met the idea of a field – a region of space in which an object experiences a force that depends on its properties. For example, an object experiences a force in a gravitational field… Continue reading 17.24 Fields and vectors

Before you read this, I suggest you read posts 17.19 and 17.22. This post uses the mathematical technique of integration (post 17.19) to explore further the concepts of centre of mass (post 17.21) and centre of gravity (post 17.22). If you don’t like mathematics, you probably won’t want to read this post. In post 17.22,… Continue reading 17.23 Integration, centre of gravity and centre of mass

Before you read this, I suggest you read posts 16.16, 17.10 and 17.21. We expect a rod, whose cross-section and density remain constant along its length, to balance at its centre. Why? The picture above shows a rod balanced in the way we expect. We could consider the rod to be made up of a… Continue reading 17.22 Balancing