How has gyroscope technology transformed smartphones? We explore its innovations, from the introduction of the gyro sensor in the iPhone 4 to its applications across various fields.
On September 12, 2024, Apple unveiled its new iPhone model, the “iPhone 16.” Although Apple has consistently introduced innovative products, this latest release has been criticized for focusing primarily on performance improvements rather than delivering the groundbreaking features many had anticipated. Consequently, some users have expressed disappointment and are recalling Apple’s former CEO, Steve Jobs. During his lifetime, he spearheaded innovation in mobile technology through the iPhone series and is widely recognized for leading the success of the “iPhone 4.”
The iPhone 4 meant more than just a smartphone. At the time, the very concept of a smartphone was still unfamiliar, and Apple succeeded in creating a new user experience with this product. The success of the iPhone 4 immediately led to explosive growth in the smartphone market and made people around the world recognize smartphones as an essential tool in their daily lives. The iPhone 4 incorporated several technological innovations, one of which was the first-ever integration of a gyroscope into a mobile phone. This gyroscope enhanced augmented reality (AR) technology and enabled new ways of playing games. It allowed the phone to accurately measure the degree of tilt and direction of rotation, which was used to revolutionize the user experience.
Until Steve Jobs unveiled the iPhone 4, many people were unfamiliar with the terms “gyro sensor” or “gyroscope.” Even those with a background in physics likely would not have imagined that the principles of a gyroscope could be applied to a smartphone. In fact, a gyroscope is a device that detects how much an object has rotated in a specific direction, and it has been widely used in aircraft and spacecraft for decades. Thanks to gyro sensors, stable flight in airplanes and spacecraft became possible, and as technologies based on this principle evolved to include mobile devices, they have become an integral part of our daily lives.
In fact, the principle of the gyroscope was invented as early as the mid-19th century and was primarily used for military and aviation purposes. During World War II, the gyroscope was an essential tool for fighter jet piloting and missile guidance, and it subsequently played a crucial role in space exploration technology. Through these technological innovations, the gyroscope gradually began to be applied for commercial purposes. Later, as gyro sensor technology became miniaturized and popularized to the point of being integrated into smartphones, it significantly improved the user experience on smart devices.
A gyroscope is a type of spinning top designed to rotate freely in space. It consists of several circular rings encircling the top; once the inner top begins to spin, it will not fall off the thin string even if placed on it, continuing to spin until it stops. You may recall playing with a toy that included a metal top and a string when you were a child.
How is it possible for a gyroscope to stay on a thin string without falling off? The law of conservation of momentum applies to objects moving in a straight line. The law of conservation of momentum states that momentum—defined as “mass of the object × velocity of the object”—is always conserved. Similarly, the law of conservation of angular momentum applies to rotating objects. Angular momentum is defined as “mass of the rotating object × rotational speed of the object × distance between the object and the axis of rotation,” and it represents the momentum of a rotating object. A good example illustrating that this angular momentum is always conserved is figure skater Yuna Kim’s techniques.
Therefore, when the top at the very center of a gyroscope begins to rotate, it generates its own angular momentum. Since this angular momentum must be conserved, even if the circular frames surrounding the top are rotated arbitrarily, the top maintains its rotational axis and rotational speed exactly as they were. Consequently, even if the spinning top’s axis is placed on a thin string, the axis and rotational speed are maintained, allowing the top to remain on the string without falling off.
Gyro sensors were designed based on this principle of the gyroscope. Inside the sensor, a spinning top rotates at high speed, similar to the innermost top. Due to the law of conservation of angular momentum, this high-speed spinning top acts as a fixed center that remains unchanged regardless of any situation (rotation). This spindle is surrounded by three circular frames representing the X, Y, and Z axes. If an object equipped with this sensor rotates 30° along the X-axis, the circular frame representing the X-axis inside the sensor also rotates 30° relative to the central spindle.
So how has this gyro sensor contributed to the development of airplanes and spacecraft? A driver of a car moving on the ground can tell whether the car is running smoothly with its wheels on the ground by looking at objects such as street trees or buildings. However, pilots of aircraft cannot see reference points like street trees or buildings, so they have no way of knowing whether the aircraft is heading toward a nosedive, flying upside down, or spinning in circles. In the days before gyro sensors, operators had no choice but to rely entirely on their physical senses—specifically their perception of gravity—to determine whether the vehicle was in the correct orientation. However, since the invention of gyro sensors, operators have been able to maintain the correct orientation by monitoring the degree of rotation detected by the sensors.
Furthermore, as autonomous driving technology continues to advance, gyro sensors are playing an increasingly vital role. Gyro sensors have become an essential technology not only for automobiles but also for various machines—such as drones and robotic vacuum cleaners—that move autonomously. As such, gyro sensor technology is being applied to an ever-wider range of fields, and its scope is likely to expand infinitely in the future.
