weather wind [2] [information over pictures]

Wind is the movement of air masses around the Earth. The movement is caused by the difference in the air pressures of these air masses. This is shown here over a map of Australia.	These air masses are either: areas of low pressure [L] or areas of high pressure [H].	Here is a satellite picture showing a high pressure area and a low pressure area over the UK.
High pressure areas [H] always move towards low pressure areas [L].	High pressure areas [H] are areas of cool, dry and usually good weather. Whereas, low pressure areas [L] are areas of warm, moist and usually bad weather.	By now you must be wondering how do you measure air pressure. This object is called a barometer and it measures air pressure in units called millibars.

Look at all of the pictures in turn. As you hover over each one a blue screen appears with an explanation of what the picture shows. Important words are coloured. If you are certain that you know about the picture click on it and it will disappear. As you go through all of the pictures you will get rid of all those which you know about and be only left with those you may be unsure of. In some cases you may get rid of all of the pictures in which case you are ready to move on to other activities which will test your knowledge on that particular topic.