According to calculations by Dr. Drang's LeanCrew blog, the iPhone 15 Pro is lighter than the iPhone 14 Pro not only because of the switch from stainless steel to titanium but also because of the change in the phone's moment of inertia.
IT House noticed that the iPhone 15 Pro weighs 187 grams, which is 9% lighter than the iPhone 14 Pro’s 206 grams. At the press conference, Apple emphasized that the lightness of the new phone was achieved by switching from a stainless steel frame to titanium. Those media reporters who have experienced the iPhone 15 Pro have noticed that the phone is lighter in the hand.
And new analysis shows that the iPhone 15 Pro feels lighter not just because it weighs less, but because its moment of inertia has also changed. Rotational inertia is a basic concept in physics, measuring the ability of an object to resist rotational motion. Its value is determined by the mass and mass distribution of the object. The farther the mass is from the object's axis of rotation, the greater the moment of inertia. Therefore, for commonly used items like smartphones, the amount of rotational inertia plays an important role in whether they feel heavy or light in daily use.
The material of the iPhone 15 Pro frame is changed from stainless steel to titanium, which plays a key role in this change because a large part of the weight reduction of the new machine is concentrated on its outer frame. Dr. Drang believes that by mainly reducing the mass of the outer frame, Apple has achieved a more significant reduction in the moment of inertia of the phone than simply reducing weight. This will make the iPhone 15 Pro easier to rotate, making it lighter than the 14 Pro.
Based on an analysis of the new phone’s dimensions, and assuming that the mass reduction is mainly at the phone’s frame, the iPhone 15 Pro’s moment of inertia is estimated to be reduced by 14–15%. Overall, this means that the iPhone 15 Pro is not only lighter but its mass is distributed in such a way that it has a lower moment of inertia, which makes the phone feel lighter.
