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Science corner

Sophie Duncan senses how the earth shakes

This highly ornate object is an earthquake detector. The Chinese were the first people to develop such an instrument. In around 130AD, a Chinese philosopher, Chang Heng, designed a detector to provide a warning system. The instrument was made up of a jar (two metres in diameter) with a central pendulum.

This pendulum would swing when the earth vibrated. The dragons' heads were connected to this pendulum. Each head had a hinged mouth, in which was a small ball. When the pendulum moved, some of these would open, dropping the balls into the toads' mouths. This could give an indication of the direction of the earthquake.

It has been recorded that Chang Heng successfully detected an earthquake many miles away using this device, and that it was some weeks before news of the earthquake reached him and his detection was validated.

Earthquakes are far more common than we realise, as the majority are too small to be felt. More than three million earthquakes happen every year, around one every 11 seconds. Most earthquakes are caused at the boundaries of the "tectonic plates", where these masses of the earth's crust push together.

Nowadays scientists use seismometers to detect these earthquakes, and seismographs are used to record traces of activity over time. Science Year was launched with an experiment involving thousands of children jumping up and down and measuring the results on home made seismometers.

You can find out how to make your own seismometer, and the results from Giant Jump experiment at Sophie Duncan is a physicist and programme manager with Science Year

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