Is the world getting heavier and how many chemicals are there?

We explore some of the curious questions that science can answer

Our planet catches dust and stones every day as it travels through space (Getty/iStock)

Is the world getting lighter or heavier?

The Earth catches around 500 tonnes of dust and stones every day as it travels through space. In its 4 billion-year history, it has put on about 16 million million million tonnes. This accounts for less than 1 per cent of the Earth’s total mass. But it has gained weight over the years. 

Does it rain harder at the edge of clouds or in the middle?

During a rainstorm it tends to cloud over first before the rain comes, implying that rain comes from the centre of the cloud. But this really depends on what you mean by the edge of a cloud. Rain clouds seem to fill the whole sky and whether you can refer to these clouds as one or more is debatable.

Rain falls when the droplets acquire enough water to be too heavy to be held suspended in the air. At the edge of the cloud there is less water (ie, less cloud), and so raindrops are less likely to form.

Small rain clouds tend to be pyramidal in shape and consist of a single convective cell. The intensity of the rain depends on the concentration of drops that are big enough for their terminal velocity to overcome the updraught which is associated with convection.

The size of the drops depends to some extent on the length of time that they spend growing within “the cloud, and as this in turn depends on the depth of the cloud, bigger drops are produced towards the centre, where the cloud is thickest.

The same is true of rain associated with frontal systems. Common experience of the persistent rain associated with warm fronts suggests that the rain starts as drizzle from fairly thin cloud, and increases in intensity as the thickening cloud sheet passes overhead.

But large storm clouds, in particular those associated with tropical rain events, may have a more complicated structure, with many cells. Often the cloud regenerates at one edge as incoming warm, moist air is forced upwards over the cold, dense downdraught, which forms the gust front. In this case the active, leading edge of the storm will correspond to the most intense rain and the intensity will decrease as the remainder of the cloud passes overhead. In such a storm, maybe 30 per cent of the rain will fall in the first 30 minutes as the leading edge passes over. The remainder will fall with decreasing intensity over the next few hours.

What causes the northern lights?

The northern lights, or aurora borealis, are caused by the interaction of the solar wind of charged particles streaming out from the sun, and the magnetic field which surrounds the Earth. Particles are trapped within the magnetic field until they enter the upper atmosphere, where they collide with molecules in the air. This generates the light. There is a greater chance of an aurora occurring when the sun is experiencing its greatest activity.

The sun goes through an 11-year cycle, and the chances of seeing an aurora are highest when sunspots are at their peak.

How fast is the Earth spinning?

It depends where you are. On the equator, where the circumference of the Earth is about 40,075km, the rotational speed with respect to an imaginary line through the Poles is about 1,670km/h, or just over 1,000mph. In the UK, where the distance travelled in 24 hours is only 26,000km, we are travelling at 1,080km/h, or 675mph.

How many chemicals are there?

Chemicals and compounds are made up of different combinations of elements. We can say how many different elements there are, but you could argue that the number of compounds of these is infinite.

To date, 116 elements have been discovered. Elements are the building blocks of other compounds. The number of compounds is growing all the time as scientists create new substances, so we can’t name a figure.