Football physics: The "impossible" free kick - Erez Garty

Summary

In 1997, Brazilian footballer Roberto Carlos scored one of the most iconic goals in history, executing a 35-meter free kick that defied expectations. By applying the Magnus effect, a phenomenon discovered by Isaac Newton, Carlos made the ball curve dramatically toward the goal. The ball’s spin created a pressure differential, bending it around the defenders and into the net. This technique, known as a 'banana kick,' is difficult to master due to precise timing and force. The Magnus effect also explains the physics behind other spinning objects, such as golf balls and frisbees, though a 'boomerang' goal remains impossible to achieve.

Takeaways

• 😀 Roberto Carlos scored an iconic free kick in 1997 during a match between Brazil and France, demonstrating remarkable precision and skill.
• 😀 The ball appeared to veer wide, but due to the Magnus effect, it curved into the goal, creating one of the most unforgettable goals in soccer history.
• 😀 The Magnus effect occurs when a spinning object causes a difference in air pressure, which results in the object curving in the direction of its spin.
• 😀 Carlos applied a spin to the ball, which caused air on one side to move slower, creating high pressure, while the other side moved faster, creating low pressure.
• 😀 This pressure differential was the key to the ball's bending flight path, illustrating the physics behind the 'banana kick'.
• 😀 The precision required to execute a successful 'banana kick' is incredibly challenging—too fast, too slow, too high, or too low can result in a miss.
• 😀 The Magnus effect is not exclusive to soccer; it also explains the flight of golf balls, frisbees, and baseballs, all of which are influenced by spin.
• 😀 Sir Isaac Newton first documented the Magnus effect in 1670, observing it while playing tennis.
• 😀 Despite its awe-inspiring nature, it’s impossible to kick a ball hard enough for it to boomerang back to you, as the ball would spiral into smaller circles.
• 😀 To achieve the required spiral for a boomerang-like return, the ball would need to spin over 15 times faster than Carlos's famous kick, making it physically unfeasible.

Q & A

What is the Magnus effect?

The Magnus effect is a phenomenon where the spin of an object, such as a ball, creates a pressure differential in the surrounding air, causing the object to curve in the direction of its spin.

How did Roberto Carlos score his famous free kick?

Carlos scored his remarkable free kick by applying a spin to the ball, causing it to curve in mid-air, bypassing the defenders and landing in the goal.

What physical principle explains the curve of the ball in Roberto Carlos's free kick?

The curve of the ball is explained by the Magnus effect, where the ball’s spin creates a pressure difference on either side of it, resulting in the ball curving toward the area of lower pressure.

Why is it difficult to execute a perfect free kick like Roberto Carlos's?

Executing a perfect free kick requires precise control over the ball’s speed, height, and direction. Small mistakes, like the ball being too high, low, fast, or wide, can lead to failure.

What would happen if you kicked a ball hard enough to make it boomerang back to you?

Even if the ball didn’t hit any obstacles, the angle of its deflection would increase, causing it to spiral into smaller and smaller circles until it stops. It would also require the ball to spin more than 15 times faster than the speed in Roberto Carlos's famous kick.

What is the primary factor that allows a ball to curve during flight?

The primary factor that allows a ball to curve is the spin applied to the ball, which causes a differential in air pressure on either side of the ball, resulting in a curved path.

Which sports, besides soccer, also demonstrate the Magnus effect?

The Magnus effect also applies to golf balls, frisbees, and baseballs, where the spin of the ball influences its trajectory.

Who first documented the Magnus effect and how did he discover it?

The Magnus effect was first documented by Sir Isaac Newton, who noticed the phenomenon while playing a game of tennis in 1670.

What is the role of air pressure in the Magnus effect?

The difference in air pressure on either side of a spinning object causes the object to curve in the direction of the lower pressure. This is the key mechanism behind the Magnus effect.

Why doesn't a ball actually return to the kicker if kicked with extreme spin?

The ball would eventually spiral into smaller circles, slowing down until it stops, rather than returning to the kicker. The forces involved prevent it from completing a full boomerang path.