# How does the wind manage to topple things like wheely bins over? With the bins being big objects how is this possible? asks Imran (10)

A useful place to start Imran would be to look at the way in which wind is can exert a very strong force. Wind is created by the Sun warming up the ground around us and the air. Sorry team, I don’t think the wind does much pulling.

Air is made up of tiny molecules. When molecules are heated, they move faster. As they move faster they become become spaced farther apart, which makes the air less dense (meaning that there are fewer molecules in a given volume). This also means that the air has a lower overall pressure (pressure is the push of the gas on it’s surroundings. In comparison, cold air is made of more tightly packed molecules, and so it is denser and has relatively higher pressure.

The warmer, lower pressure air begins to move upwards and therefore it creates space below it which is filled by the colder higher pressure air. A wind is created. The hotter the air near the surface of the Earth the lower the pressure and the faster the rise. The 2017 hurricanes were caused by the hot sea and hot temperatures near the surface.

Can you measure how much push (force) is needed to push over a wheely bin?  Let’s first make our own push-pull measurer. You will need an elastic band, cotton reel, a couple of drawing pins, some sellotape and a paper clip to make your own measurer.

You can use it directly to measure pushes and pulls just by seeing how far the cotton reel moves up the dowel rod. It would however be better if we calibrated the rod in some way. In the images below the rod has been calibrated in Newtons (theses are the units of force). To do this a 500 gramme mass was attached to the hook. It is known that a 500g mass will exert a force (pull) of 1/2 Newton. So when the mass is attached, the elastic band will stretch, and the dowel rod will be pulled down. The distance on the rod between the ‘no’ force point and the 500g point is therefore equivalent to half a Newton.

It is estimated that an 80 mph wind would have a push of about 400 Newtons per square metre and be able to move a car. A breeze 5 mph might have a push of between 5-10N per square metre. You could try your meter on a sheet of cardboard in a strong breeze and see what you get.

Imran your question was very interesting to answer and you might have some difficulty in understanding some of the stuff above. If that is the case and also for anybody else reading this PLEASE ask another question or make a Comment.