Cut out goal and leg shapes along the black lines. Fold along the dotted lines and secure the joins with sticky tape.
You now have two goals and two feet for two people (to be placed on your fingers).
Using plasticine, make two solid boots or feet. Attach these to the leg cut-outs (this is optional).
Set up the playing field on a table top or somewhere easy to reach.
Start to practise your game, and kick the ball (marble) around with your fingers.
Try to kick some goals.
Try to curve the ball by kicking it with the side of your finger-boot. Look at the patterns on the marble; is it spinning?
When you have perfected your scientific small soccer skills, challenge your friends to your very own Mini World Cup.
What's happening?
How does a ball curve? It is all about the aerodynamics of the ball, which needs to be spinning for it to work.
In real soccer, a curving ball is spinning into the oncoming air. As it does this, the air pressure around the spinning ball is uneven. The side of the ball that is moving in the same direction as the air flow will have faster moving air than the side that is spinning away from the direction of air flow.
Faster moving air is under lower pressure than slower moving air (this is sometime referred to as Bernoulli's principle).
The ball curves towards the side that has lower air pressure. Researchers propose that the air that is at a higher pressure pushes the ball over and into the lower pressured space. Note this all happens when the ball is in the air, and is not so relevant when it goes along the ground. In your Mini World Cup any curve you see on the ball is mostly due to the spin put on the marble, not pressure differences, but we can't all bend it like Beckham!
The first explanation of the lateral deflection of a spinning object (ball curving) is credited to work done by the German physicist Gustav Magnus in 1852. Magnus had actually been trying to determine why spinning shells and bullets deflect to one side, but his explanation applies equally well to balls.
The speed at which the ball is moving is also very important. A faster moving ball will have less drag and therefore take longer to slow down than a slower moving ball.
What this means for a football is that a slow-moving ball with a lot of spin will have a larger sideways force than a fast-moving ball with the same spin. So as a ball slows down at the end of its trajectory, the curve becomes more pronounced.
Applications
You can kick impressive goals. The same physics also has effects in other ball sports, especially cricket where spin and swing bowlers appear to give the ball a mind of its own, but it's all physics (and a bit of skill) punters.
Pressure differences and how objects behave in them have far broader aerodynamic applications and are used in designing everything from paper planes to fighter jets.
