# 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.

# Mariah (7) asks “Why are pushes and pulls forces?”

Thanks team and thanks Mariah for the question.  My team are quite correct there are lots of pushes and pulls. Can you think of more? What about gravity? That pulls things to the ground. What about the wind, that pushes things.

In science and in our daily life we put things into groups. The things in the group all have something in common. All fish are grouped together, they can all breathe underwater. Can you see anything else they have in all fish have which is the same?
All bicycles are grouped together, they all have two wheels. They also have some other things in common (the same).

If all forces are grouped together , they all involve pushes and pulls. The group that pushes and pulls is called forces.

# “What is the difference between speed and velocity” asks Sayed(11)

Absolutely right my friends. The two cars have the same speed but they are going in the opposite direction so their velocities are different.

An interesting example of the difference between
speed and velocity is when you look at an object moving at a certain speed in a circle. The speed is constant BUT the velocity is constantly changing as the object moves around the circle, see V1 and V2. The velocity at 1 is drawn as a line (representing the speed) pointing in the direction V1. This is a ‘vector’.

Sayed – this site is mainly directed at 8-13 yr olds so the answer above is very ‘general’. I have published it because younger readers might be interested in the difference between the two terms …for more information visit this site.

# Imran (age 10) asked “If I was to push a ball , how does it stay moving even after I pushed it?”

Imran. A great question. I would like to answer it in a slightly different way (you can sometimes do that with questions). After you push a ball it starts moving but does it stay moving?

When you push the ball you transferring your push (force)  to the ball and it moves. Newton (a great scientist and questioner) thought “Why does it stop moving? I have transferred my force to the ball and it should keep moving until it transfers that force to something else” But it does stops moving. I put this question to my friends and they came up with the following thoughts.

Why not investigate moving balls over different surfaces. You could use wood, paper, carpet, or the floor as surfaces and see how far the ball rolls BUT you have to make it a fair test. How do you create the same force?  How do you transfer the same force to the ball?

What would be your prediction (educated guess) about what the result would be? All scientist’s make predictions and then they test them.  My last question is, if there is something stopping the ball from rolling …. what do you think it is? has it got a name? If you have an answer you can leave it in the  ‘Leave a Reply’ box below. Want to ask another question …go to