weather [wind] [4] [information over pictures]

The speed of air movement and therefore the air speed is measured using a cup anemometer as seen here. The normal unit of wind speed is the knot (nautical mile per hour = 0.51 m sec-1 = 1.15 mph).	The Beaufort scale is named after Sir Francis Beaufort estimates wind strength without the need for instruments and based on the numbers 0 - 17. This first example is: 0: Calm and still winds. Smoke rises vertically.	This second example is: 2. Gentle wind at 6-11 kph (4-7 mph). Wind can be felt on face; flags ripple.
This third example is: 4. Moderate wind at 20-28 kph (13-18 mph). Paper and leaves scatter.	This fourth example is: 6. Strong wind at 39-49 kph (25-31 mph). Umbrellas are hard to use; large branches on trees move.	This fifth example is: 8. Gale at 62-74 kph (39-46 mph). Twigs and branches break off trees.

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.