September 2, 2010, 2:41 pm
Best ever free kick scores due to molecules!
Never thought of top football players using fancy laws of physics to score their best goals? Think again!
What was discovered?
The amazing goal by Roberto Carlos for Brazil against France in 1997 was scored from a free kick 115 feet (35 metres) away from the goal!
The spin on the ball as it passed through the air allowed it to follow a curve as it approached the goal. Air resistance due to atmospheric molecules helped to slow down the ball, but many people thought that the final twist of the ball into the goal must have been caused by a gust of wind.
Not so, according to experiments which showed that the slowing effect of air molecules allowed the spin of the ball to have a much greater effect on the curved path into the back of the net...
The amazing goal was due to the skill of the player, and not some random gush of wind!
Of course it was not possible to have Roberto Carlos repeat his amazing feat many more times, so the next best thing was to set up a model:
A sling shot was used to hurl tiny plastic ball through water and the velocity and spin of the ball was recorded along with the path it followed (the trajectory)
Why is it important?
Ha! Any football fan will agree that the skill of a player in such a moment is breathtaking, so to have the event confirmed by science should warm the hearts of millions... and enlighten us to the trajectory of spinning objects too!
Why does a spinning ball have a curved path?
The trajectory of spinning objects has been known to have a curved trajectory for many years - this is known as the Magnus effect
The spinning ball creates a whirlpool of air around it, and experiences a force perpendicular (at right angles, 90 degrees) to it, causing the ball to curve.
So what's new about this study?
It's the final rapid twist of the ball which was so mysterious - as if a gust of wind had changed the ball's path.
By doing many experiments and taking measurements for analysis, this final twist was explained as a phenomenon that depended on the air slowing down the ball as it travelled, to a point where the spin had a greater turning effect... straight into the goal!
This can only occur in shots taken over a long distance - so if you are a striker, don't expect too much help from the final twist... it takes A LOT of practice!!!