The Magnus Effect of a Ball in Sports
Sportsmen and sportswomen who play ball games such as cricket or baseball know all about spinning the ball in the air. They can use the ball not only to make it change direction when it hits the ground, but also make it curve in the air. In baseball, golf, cricket (except a fast bowler in cricket), all this is done with the use of spin by a technique that requires a lot of practice. The Magnus effect is a great advantage to win games.
So why do and what makes a ball spin and curve in the air? Well this was a question answered in the early 20th century by the British scientist Lord Rayleigh (John William Strutt), who called it the 'Magnus Effect'. This was named after a previous German scientist Heinrich Gustav Magnus.
Generally, as a spinning ball travels in the air, it drags air around itself in the direction of the spin. The air moving past the ball is also speeded up on one side and slowed down on the other. Since air moving faster also exerts less pressure, the air on the opposite direction of the ball is at a relatively greater pressure. It is this specific difference in pressure that creates the force which makes the ball to curve in flight.
The Magnus Effect is evident in many particular sports. A lot of top tennis players can create a top-spin lob and which seems to be going 'out' but drops sharply before the baseline. A golfer imparts a spin automatically when driving the ball, so that the ball hisses away from the tee at around 160 kilometres per hour (100 mph) with a back spin of around 50 RPS (revolutions per second). The spin initially counteracts the effect of gravity which enables the ball to fly in a straight line rather than in a curved trajectory. With the highest-number irons which create better and greater spin in golf, the ball can even be seen to climb. If the shot is miss-hit with the club's head at an angle, which many golfers realize, the same force can take the ball away sideways into the rough.
In baseball, a pitcher uses different kinds of hand grips to impart different spins, and thus different curves to the ball. The 'curve-ball' is a curve that breaks downwards and away from the batter. Some pitchers throw a so-called 'fade-away' or 'screw-ball', curving the ball towards the batter. A 'slider' breaks sharply at the last moment. These sort of curves require spins of up to 38 rps, and which can induce a swerve of some 2 feet in the 60 feet between the pitcher's mound and home plate.
In American football and rugby, the similar effect can be used as well with great skill and technique. An elongated ball kicked to spin around its long axis will go straight while traveling along the line of that axis. Only when it starts to drop, and the spin axis is different to the line of travel, does it begin to swerve. A professional player can therefore kick a ball parallel to the touchline, fully aware that it will curve out of play once it drops back to the ground.
In cricket, a curve or swing can be produced without the need of a spin. This is usually done by a medium to fast bowler making wise judgment of the single raised seam. The seam induces a slight air turbulence and causing the air to flow more rapidly over one side of the ball. As before, a different speed of airflow on the two sides will produce a difference in pressure causing the force that swings the ball in flight. A lot of skilled bowlers increase the difference in roughness between the two sides of the ball by rubbing and polishing one side of it on their trousers.
The Magnus Effect in Flettner Ships and Flettner Airplanes
As a Magnus effect is a spinning sphere that is mostly used by football players, cricket bowlers, baseball pitchers, golfers etc, this important study of physics is also evaluated on the engineering side of using it on rotor ships and Flettner airplanes. The use of the Magnus effect on ships has been tested and proven by the German aviation engineer Anton Flettner(1885-1961). In 1926, Flettner fitted rotors to a ship called Buckau and completed an Atlantic journey.
The first and original concept of this great technology was described as making use of wind power. However, this was proven incorrect because the power that the Flettner rotors on the ships give is not exactly wind power as many people understood, it is really exploiting the Magnus effect. The Flettner rotors was designed for this kind of propulsion. The cylindrical rotor has disc end plates which is spun along its axis They are mounted upright on the ship. The Magnus effect creates an aerodynamic force on the rotors with the work of the wind. They are rotated by the ship's engines and act like sails to propel the ship.
A Flettner airplane also uses a Flettner rotor to assist the plane to lift off. The rotor airplane has a spinning cylinder with circular end plates just like the Flettner ship. The Magnus effect comes into force when the aircraft starts to move forward, and the air pressure differential makes the airplane lift in the air. The technology is very similar to the way an airplane wing lifts a plane up, and a spinning cylindrical rotor can also do the job. Anton Flettner's concept is very simple to understand in the field of physics. A spinning football for example uses the Magnus effect to put a certain distance between the ball and a large rock wall, whereas a cylindrical rotor uses an internal combustion engine as a power source to spin it fast to use the Magnus effect. This in general, puts a certain distance between the ground and the airplane.