After two years, the weight of iPhone 15 Pro has finally returned to within 200 grams.
Estimating the time, I believe that some users who purchased iPhone 15 Pro have already received the actual device. Users who are sensitive to the weight of their phones may be pleasantly surprised to find that this year’s iPhone 15 Pro feels lighter.
Last year’s iPhone 14 Pro weighed 206 grams, while this year’s iPhone 15 Pro weighs 187 grams, a 9% reduction compared to last year. This has a lot to do with the titanium alloy frame.
The titanium alloy used in iPhone 15 Pro is grade 5 titanium (Ti-6Al-4V), which is a titanium alloy composed of titanium, 6% aluminum and 4% vanadium. The density of Ti-6Al-4V is about 4.43 g/cm³. The iPhone 14 Pro is made of surgical-grade stainless steel, with an average density of about 7.8 g/cm³. This means that surgical grade stainless steel is heavier than Ti-6Al-4V for the same volume.
But when you hold the iPhone 15 Pro in your hand, you may feel that its weight has been reduced by more than 9%. Is this an illusion?
In fact, the lightness of the hand is not only determined by the titanium alloy material of the new iPhone, but also related to a classic mechanical principle.
Rotational inertia is a basic concept in physics. It is used to measure the resistance of an object to rotational motion. Its value is determined by the mass and mass distribution of the object. The farther the mass is from the rotation axis of the object, the greater the rotational inertia.
Therefore, for a commonly used device like the iPhone, its rotational resistance plays a crucial role in the feel.
Apple replaced the iPhone 15 Pro model with a titanium alloy frame, which caused a large part of the weight reduction to be concentrated on the edges of the phone, which in turn affected the moment of inertia of the phone. In response to this change, a doctor named Drang made A computational analysis.
▲The figure above shows the calculation process.
Dr. Drang first assumed that the iPhone 14 Pro and iPhone 15 Pro have the same size, 147.5 mm high and 71.5 mm wide respectively, and set the origin at the geometric center of the phone. By default, the iPhone 15 Pro has uniform quality, thus calculating the iPhone 14 Pro and iPhone 15 Pro's moment of inertia around the X-axis.
The final result is that the moment of inertia of the iPhone 15 Pro around the It may be more effortless to move, giving a feeling of lightness during use.
Of course, Dr. Drang's calculation is only a preliminary calculation. To make a more accurate calculation, more detailed information and accurate measurement data are needed, but the overall idea is persuasive. In other words, by changing the frame design of the phone, its moment of inertia can be reduced, thereby further creating the "light and airy" feeling of the iPhone 15 Pro.
To help you better understand the moment of inertia, let's take two simple examples. Imagine that you are holding two windmills of different sizes, both fixed on sticks of the same length. When you try to stop them from rotating, You will find that you need to use more force to stop a large windmill, while it is relatively easy to stop a small windmill.
This is precisely because a large windmill has more "mass" distributed away from the center, so its ability to resist stopping is stronger. This ability to resist rotational changes is what we call rotational inertia.
If you still don’t understand the moment of inertia, you might as well give a more vivid example. When you try to turn the wheel of a bicycle quickly, the larger the wheel and the heavier the weight, the more obvious resistance you will feel. The larger and heavier the wheel, the greater the moment of inertia and the more obvious resistance. Therefore, this is why in bicycle racing Medium, the tires are thinner and easier to accelerate.
These examples are just the tip of the iceberg when it comes to applications of moment of inertia in daily life. The concept of moment of inertia is widely used in daily life. For example, products such as tennis rackets and golf clubs in the sports field, and gyro stabilizers in the digital field all use this knowledge.
In short, any scenario involving rotation is likely to involve the concept of rotational inertia.
If you pay attention when watching daily competitions, you will find that when artistic skaters on the ice perform spinning movements, they will tighten their arms to increase the rotation speed, but before landing, they will spread their bodies to slow down the rotation speed. . This involves the principle of moment of inertia.
Therefore, the lightness of iPhone 15 Pro is not a coincidence, but uses titanium alloy as the medium to exquisitely balance the weight and moment of inertia of the phone, allowing users to experience a lighter and more comfortable feel.
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