# 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.

# How strong is a thunderstorm? -asked Jessica (8)

Many thanks for your comments team. Yes you are right, to create a thunderstorm you need a lot of warm water. It’s development goes by the following crude set of stages …

• Lots of warm water evaporates (turns from a liquid state into a gaseous state.). Thunderstorms are therefore more common in the warmer regions of our planet.
• The gaseous water is forced upwards by the warm sea. The warm sea warms the air close to it. This air expands and is therefore becomes ‘lighter’ and moves upwards carrying the water vapour (water vapour is the term used to describe gaseous water) with it.
• As the gaseous water rises it gets colder (more distant from the warm sea) so it becomes water again (small drops of liquid water). A cloud begins to form.
• The heat from the ocean continues to make the water and water vapour(clouds) rise.
• It gets even colder and more of the water vapour turns back to water.
• Some of the water droplets in the cloud turn into ice particles.
• The ice particles separate some move to the top of the cloud others remain in the bottom.
• This split causes an uneven distribution of electrical charge in the cloud.
• The result is Lightning and Thunder.
• Some of the frozen water falls away from the cloud. this causes all sorts of down draughts and strong winds are created.
• Some of the ice does not melt as it falls through the air – this forms hailstones.

You could look at this question http://www.sciencemaster.co.uk/2016/11/18/elizabeth-9-asked-a-question-on-lightning/

# Maryam (age 10) asked a question on forces. “What do forces have to do with science?”

Maryam

What an excellent question. How do I answer this? Firstly I think we need to know what we mean by science. Here is what my friends said when I asked them the question.

My favourite definition of science is that it is ‘applied curiosity’. People who enjoy science have a curiosity about the physical and natural world that surrounds them. This leads them to investigate it.

Look at the see-saw in the picture above. Why does a small mass seem to balance a larger mass? Lets move the masses around and see if we can get other positions where they balance? This is curiosity in action.

So what about forces, are they part of the natural world or the physical world? What is a force?

The forces we meet every day are pushes and pulls. Pushes and pulls make things move.

Gravity is another force … jump off a chair and you are pulled to the ground, you moved because of the pull of gravity. Another force is friction – how does that affect movement? Force and movement are therefore intertwined. Investigate movement and you are investigating forces. And that leads to lots of questions. Do things always move at the same speed when a force is applied? Curiosity, curiosity, curiosity.

So please show your curiosity by asking more questions and I leave you with a question of your own. Are forces part of the natural world or the physical one, or both, or neither?

I hope this gives you some answers to your excellent question. Any more questions?