| Saving 20 grams of stationary mass is equal to saving possibly 200 grams in quick movement, such as taking the phone out of a pocket quickly. This is going to be quite noticeable. Add in to this the authors calculations of rotational inertia savings of 15% the effect might be even more pronounced. So when moving the phone from pocket to quickly see a message or phone call, those savings reduce the weight of the phone during this motion by almost the weight of the phone itself. Definitely noticeable. ----- A few years ago I tried to work out the stationary weight limit of my roof rack on my 4wd, for example if I wanted to mount a rooftop tent with two adults (I'm overweight at the moment) and wanted to know if my size was an issue. Assuming a stationary weight of tent and other stuff and me and my partner I pushed my estimate to 400kg. The roof rack is rated at 100kg carrying capacity. What does 100kg equal to when going up and down sand dunes? I found a forum post where someone worked out with calculus the "weight" that 100kg turns into 700kg - 800kg whilst off-roading aggressively, the roof rack experiences almost 80% of a ton due to the acceleration/deceleration pressing into and away from the car in a vertical diagonal motion. With that I could rest easy knowing I'll never approach those numbers whilst the vehicle is stationary. ------ I figure that quick motion moving the phone from pocket to in front of your face involves similar forces. Intuitively this checks out. Hold your phone in front of your face. Now move quickly side to side. Your phone is easily exerting 1kg of force as you wave it around. That 20 grams saving will make a huge difference. |