The intriguing phenomenon known as the Magnus effect can be witnessed when a spinning object navigates through a fluid (be it a gas or a liquid), and there's a relative motion between the two. The spinning object's trajectory tends to deviate in a manner that is quite distinct from a non-spinning object's path. This deviation can be attributed to the pressure difference of the fluid on the opposite sides of the object in motion.
In layman's terms, a spinning object generates a sideways force. The magnitude of the Magnus effect is directly proportional to the speed of rotation. This is the very reason why a soccer player can curve a soccer ball past a wall of defenders into the net, or why a cricket ball behaves the way it does during a conventional swing bowling.
The effect derives its name from the German physicist Heinrich Gustav Magnus, who first described it in 1852. While other scientists like Sir Isaac Newton had previously explained this effect, it was Magnus who received the recognition. Let's delve deeper into this topic.
Observations
Have you ever been amazed at how a soccer player manages to curve a ball around a wall of defenders to score a goal? This is the Magnus Effect at play. But causing the ball to curve in mid-air is not as straightforward as it seems. Certain principles of physics make it possible. The Magnus effect comes into play with spinning objects that are spherical or cylindrical. The object's spin alters the airflow around it, and due to the conservation of momentum, the Magnus effect is produced.
Is the Magnus Effect reliant on Bernoulli’s Principle?
The Magnus effect is often thought of as a specific instance of the Bernoulli’s principle. According to Bernoulli’s principle , the pressure of a non-viscous fluid decreases with an increase in fluid speed. However, in the case of a spinning ball (a classic example of the Magnus effect), the rotating ball creates a vortex of fluid (air) around it and experiences a force perpendicular to the direction of motion. In the Magnus effect, we consider the viscosity of the fluid, while the Bernoulli’s principle is applicable for fluids without viscosity. Therefore, the Magnus effect is not dependent on the Bernoulli’s principle.
The Working Mechanism of the Magnus Effect
To make the ball curve to the left while airborne, you need to impart an anticlockwise spin to the ball while propelling it forward. If you're using your right foot to kick, you need to kick it powerfully from the inside of your foot so that the ball spins anti-clockwise while moving forward. Essentially, you need to strike it off-centre. As the ball moves forward, it encounters air from the opposite direction. The air on the left side of the ball moves along with the spin of the ball. This stream of air moving on the left side of the ball gets accelerated and veers towards the centre of the ball.
The air on the right side of the ball moves contrary to the spinning ball. This column of air moving on the ball's right side slows down and continues moving straight. The air on this side of the ball doesn’t move towards the centre.
The asymmetrical movement of air around the ball alters the original direction of the ball. A net force is exerted in the direction depicted by the arrow in the figure.
At this point, Newton’s Third Law of Motion comes into play. According to Newton’s third law of motion, every action produces an equal and opposite reaction.
Just as a rocket propels upwards when the gas is expelled downwards, the force depicted by the violet arrow in the image generates a counter-force in the opposite direction (shown by the pink arrow). This results in a change in the ball's direction. This process repeats itself, causing further deviation of the ball as it progresses.
The Magnus effect holds significant importance in the study of the physics behind several sports that involve a ball. Additionally, it is critical in the defence sector, where this effect aids in studying the effects of spinning on guided missiles. It also finds use in engineering applications, particularly in designing aeroplanes and rotor ships.
The Magnus effect is primarily used in sports such as soccer, golf, cricket, tennis, baseball and others. Understanding this concept is crucial to grasp the physics behind many ball sports.
Some aircraft have been constructed that use the Magnus effect for lift by using a rotating cylinder at the front of a wing, which enables flight at lower horizontal speeds.
The Magnus effect is also utilized in external ballistics. The combined sideways component of the wind generates a Magnus force that acts on the bullet.
Rotor ships employ Flettner rotors, which are mast-like cylinders mounted vertically on the ship’s deck, assisting in propulsion. When the wind blows from the side, a forward thrust is generated due to the Magnus effect.
The force exerted on a fast spinning cylinder or sphere travelling through air or another fluid in a direction perpendicular to the axis of spin is known as the Magnus force.
Give an example of where the Magnus effect is seen.
The Magnus effect explains how a football player may bend the ball into a goal around a five-person wall.
Is the Magnus effect an application of Newton’s third law of motion?
The Magnus effect is an application of Newton’s third law of motion. As a result of the object pushing the air in one direction, the air pushes the object in the opposite direction.