Before you read this post, I suggest you read posts 16.27 , 16.30 and 16.33. No, this post isn’t about the mole in the picture. It’s about a completely different type of mole – the mass of a pure substance that contains the Avogadro’s number (post 16.27) of molecules (post 16.30). As an example, we’ll… Continue reading 17.48 Moles
Before you read this, I suggest you read posts 17.44 and 17.45 You often see birds perched on cables that are carrying electricity but aren’t insulated. In the UK electricity can be sent through overhead cables at 400 kV. Why aren’t the birds electrocuted? As charge moves along the cable, the voltage drops. Why? Because… Continue reading 17.47 How can birds sit on high voltage electrical cables and not be electrocuted?
If you’re not a native English speaker, you may find it difficult to understand the title of this post. Peeing is a more polite way of saying the impolite word “pissing”; the words you will find in a dictionary are “urination” and “micturition”. What has this got to do with helping girls study science? I… Continue reading 17.46 Peeing contests: helping girls to study science
Before you read this post, I suggest you read post 17.44. To move charge from a point with a low potential to a point with a high potential, we need to do work. This is the same as saying that moving a charge from a point with a low potential to a point with a… Continue reading 17.45 Electrical energy
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
