According to calculations from Dr. Drang's LeanCrew blog, the iPhone 15 Pro may feel much lighter than the iPhone 14 Pro, not only because of the change from stainless steel to titanium, but also because of the change in the device's moment of inertia.
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The iPhone 15 Pro weighs 187 grams, which is 9% less than the iPhone 14 Pro’s 206 grams. Apple emphasized in its statement that the change from a stainless steel frame to a titanium frame has brought a new lightweight feel. Those who have used the iPhone 15 Pro for a while have noticed that the device feels much lighter in the hand. However, new analysis suggests that the iPhone 15 Pro may be lighter than it actually is due to changes in its moment of inertia.
Moment of inertia is a fundamental concept in physics that measures an object's resistance to rotational motion. Its value depends on the mass of the object and how the mass is distributed. Crucially, the further the mass is from the object's axis of rotation, the greater the moment of inertia. Therefore, for frequently handled objects such as smartphones, this rotational resistance plays an important role in how heavy or light they feel during daily use.
Apple's switch from stainless steel to titanium for the iPhone 15 Pro's outer band is key to this change, as much of the phone's weight savings is concentrated on its outer edges. Dr. Drang's analysis shows that by minimizing the surrounding mass, Apple has achieved a reduction in the phone's moment of inertia that is more significant than would be expected by simply reducing weight.
This reduction, more than a reduction in mass, will make the iPhone 15 Pro easier to turn, which may make it feel much lighter than the 14 Pro.
Based on the analysis of the size of the new mobile phone, assuming that the mass reduction is mainly concentrated around the mobile phone, the moment of inertia of the iPhone 15 Pro is expected to be reduced by 14-15%. In layman’s terms, the iPhone 15 Pro is not only lighter; Its design ensures that its mass is distributed in such a way that it is less resistant to rotational motion. This makes the device feel more flexible and gives a lighter impression.