What it shows
Land heats and cools much faster than water. In summer the hot Indian land has low pressure and air flows in from the cooler sea, carrying moisture; in winter the land is colder and the flow reverses. Measuring sand and water under the same sun shows the difference that drives the monsoon.
The science
Water has a high specific heat capacity, about five times that of dry sand per kilogram, and sunlight warms a deep layer of water while it warms only the top few millimetres of sand. So in the same sun the sand surface gets much hotter and at night it cools much faster. Hot land warms the air above it, the air rises and pressure drops, and air moves in from the higher-pressure sea. On the scale of India this inflow is the south-west monsoon, loaded with moisture from the Arabian Sea and the Bay of Bengal.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Two identical containers
- Dry sand and water to the same depth
- Two thermometers
- A sunny spot and a shaded spot
- A notebook and a clock
- Optional: a lamp for a repeat indoors
Safety
For this project: Handle glass thermometers gently; a digital probe is safer.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Fill one container with sand and the other with water to the same depth and let both sit in shade until they read the same temperature.
Push a thermometer bulb just under the surface of each.
Place both in full sun at 10 in the morning and read every 15 minutes for two hours.
Move both into shade and keep reading every 15 minutes for another hour.
If possible, read again at sunset and an hour after dark.
Plot both temperature curves on one graph.
Mark the peak difference and the time each took to cool back.
Write how this difference, scaled up to a whole subcontinent, produces the summer and winter monsoon winds.
What you should see
Sand rises 15 to 25 degrees above its start while water rises only a few degrees, and sand drops back fastest in shade, which is the land-sea contrast behind the monsoon.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why does sand heat faster than water?
Water has a higher specific heat capacity and sunlight warms a deeper layer of it.
2Which way does air move in summer?
From the cooler, higher-pressure sea to the hotter, lower-pressure land.
3What makes the summer monsoon wet?
The incoming air crosses warm seas and picks up moisture, which falls when the air rises over land and hills.
4Why is the winter monsoon mostly dry?
The air flows from the cold land out to sea and carries little moisture, except where it crosses the Bay of Bengal to Tamil Nadu.
Take it further
Repeat with wet sand and show how moist ground behaves more like water.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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