Before you read this post, I suggest you read posts 17.49 and 17.50. Acidity and alkalinity are important for many biological processes. Azaleas will only grow well in acid soils. Saliva is alkaline but your stomach contents are acid. Healthy urine is acidic but infected urine can be alkaline. The previous paragraph raises several questions… Continue reading 18.1 pH

Before you read this, I suggest you read post 17.49. In post 17.49, we saw that an acid is something that acts as a source of hydrogen ions; something that reacts with hydrogen ions is called a base. A base that can dissolve in water is called an alkali. An alkaline solution is a solution… Continue reading 17.50 Alkalis

Before you read this, I suggest you read posts 16.30, 16.33, 16.39 and 17.48. In 2017 there was an alarming increase in attacks in London in which victims had acid thrown in their faces. One way in which these attacks could be reduced might be to make it illegal for people to carry acids in… Continue reading 17.49 Acids

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