Before you read this post, I suggest that you read posts 16.25 and 17.17. Everybody knows that amps and volts are electrical units. But what, exactly, do we use them to measure? And, how are they connected by Ohm’s law? In post 16.25, we saw that amps (A) are used to measure electrical current. To… Continue reading 17.44 Amps, volts and ohms

The insect in the picture is walking on water. You can see that it isn’t simply floating. To float, part of it would have to be submerged so that the upward force that previously acted on the displaced water balanced the downward force (weight) exerted by gravity on the insect (post 17.6). Instead, it is… Continue reading 17.43 Walking on water – surface tension

Before you read this, I suggest you read posts 17.17 and 17.41. How can you calculate the rate of flow of a viscous liquid in a very narrow tube? The obvious answer is to solve the Navier-Stokes equation (post 17.15) for this type of flow. But that involves a lot of mathematics. We can get… Continue reading 17.42 Dimensional analysis

Most people have seen Einstein’s famous equation E = mc2.                    (1) But what does it mean? It means that if stuff with a mass m is completely destroyed, it changes into energy E, when c represents the speed of light in a vacuum. When I say, “completely destroyed”, I don’t broken or burnt (burning simply… Continue reading 17.41 Units in equations

Before you read this, I suggest you read posts 17.38 and 17.39. We are all familiar with rolling objects (a ball rolling along the ground or the wheel of a moving car); as a result, we tend not to think much about rolling and may not appreciate how complicated it is. The picture above shows… Continue reading 17.40 Rolling

In posts 17.11 and 17.12 we saw that angular displacement, angular speed and angular acceleration can be defined, as vectors, in a way that is analogous to displacement, velocity and acceleration (post 17.4) along a line (not necessarily a straight line) in space – translational motion. In post 16.12, we saw that translational motion could… Continue reading 17.39 Translational and rotational motion

Before you read this post, I suggest that you read posts 17.12 and 17.19. Let’s think about a particle (an object of negligible size) of mass m moving around a circle of radius r with a constant angular speed ω (see post 17.12). Its speed is given by v = ωr (see post 17.12) so… Continue reading 17.38 Rotational inertia

Before you read this, I suggest you read posts 17.2, 17.3 and 17.10. In post 17.25, we saw that it is often better to introduce an idea as simply as possible and to add further sophistication at a later stage. For example, in post 16.20, the idea of work was explained by the work done… Continue reading 17.37 More about torque – cross products of vectors

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