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Comment by weinzierl | Hacker News Reader

"iPhone 15 Pro 10% lighter but 15% lower rotational inertia because of edge mass"

The "but" in the title confuses me. Both are good things and make the phone feel lighter, so shouldn't it be "and"?

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The “but” is there because a 15% reduction in rotational inertia is more than you’d expect from being just 10% lighter.

The “but” is to indicate that while you’d expect to feel a 10% difference owing to mass, you actually feel a larger difference as most of the removed mass is at the edge, so the phone has a significantly lower moment of inertia.

It's not intuitive that those values don't match up.

Lower rotational inertia is definitely a downside, it is absolutely a downgrade in the critical fidget-spinning-your-phone experience.

Nowadays, I consider heavier -> better. Phones can be somewhat an exception, however it usually comes at the expense of battery, overall rigidity.

There are exceptions - using lighter materials - notably Al, Mg alloys vs steel.

A lighter phone should mean less energy applied to your screen when you drop it.

Alternatively, it means a ticker, metal infused glass pane... or there is a shock absorbing layer to prevent all the stress to be distributed through the glass pane. If you take some tools - e.g. multimeters, dropping them from 2m height is a rather standard test for their build quality/durability. Not saying I'd expect most phones to survive that, yet it's quite common to prefer the minimalist, throw away devices.

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