Before watches and clocks were invented, people used the position of the sun in the sky to guess the time of day, but this couldn’t be very accurate. The next step was the invention of the sundial, when someone noticed the way that shadows moved across the ground over the …
Sand is a mixture of small grains of rock, ranging in size from 0.0625 mm to 2 mm. Sand is made by erosion and weathering of rocks – seas or rivers carry pebbles that chip small pieces off rocks, and freezing and thawing during the winter breaks rocks up. Sand …
Clouds are collections of very small drops of water or particles of ice and they form from water vapour in the air. Types of Clouds According to the World Meteorological Office, there are ten basic cloud types: Cirrus, cirrocumulus, cirrostratus, altocumulus, altostratus, nimbostratus, cumulus, cumulonimbus, stratocumulus and stratus. The names …
Weather stations include different ways of measuring the weather. Meteorologists (people who study the weather) use weather stations to monitor the weather day by day, and use the results to make weather forecasts. Use a weather station to record the weather and see how it changes daily, weekly and monthly. …
Desalination means taking the salt out of salty water (from lakes or the sea) to make fresh, drinkable water. How Does Desalination Work? The two main ways to remove the salt (and other impurities) from water are through distillation and osmosis. In distillation, the water is heated to form a …
Condensation, on the inside of the kitchen window on a chilly morning or on a cold glass of water, and dew on the grass on a cool autumn evening, is a familiar sight, but what is it and what causes it? About Water Water molecules can be a solid (ice), …
Warm air is less dense than cold air, and so as air is warmed by the sun it rises (see ‘Warm and Cold: Expanding Air’ and ‘Floating and Sinking: Looking at Density’). Cold air then moves to replace the warm air. This movement of air is called ‘wind’. At the …
Cooking with the sun (solar cooking) provides free, safe, clean heat energy that preserves nutrients in food. Cooking with the Sun On a clear, bright, sunny day, line a mixing bowl or colander with aluminium foil (shiny side up), and smooth it as much as possible, to make a solar …
Soil erosion is the loss of healthy and fertile topsoil through water or wind, leaving behind poorer quality subsoil. Soil erosion can lead to famine in developing countries, because the poorer soil means that crops are not as good, or might fail completely. Different Soils and Water Erosion Fill shallow …
A sunspot is a cooler area on the surface of the sun, which shows up as a patch that is darker than the rest of the sun’s surface. A sunspot generally lasts for about two weeks. Sunspots usually happen in groups. Sunspot activity happens in cycles that peak about every …