
The common position for holding a tablet (ignoring some details) works like this (assuming an 90° degree holding):
(Force*.06)(22*(.09+.06))(7.2*.4) = 0
Assuming somethings I don't want to discuss (but I think they stand for more or less the average), where 7.11 = weight of the Touchpad in Newtons.
The formula for the iPad 2 is:
(Force*.06)(22*(.09+.06))(5.78*.4) = 0
So, the Force needed is (one muscle for each case, other muscles the calcs are relatively similar):
Touchpad: 103 N
iPad 2: 93 N
Let us imagine (IMAGINE, all the following is an oversimplification) your strengh + stamina is 2 hrs with the Touchpad, let us imagine you use 103 N/minute, so 180 * 103 N = 18,540 N, the same amount energy will get you 199 minutes with the iPad 2, that's 19 minutes more (relative to a single muscle, of course, if one muscle gives up, it is enough for you to give up...). Also, this numbers varies according to many factors (specially holding), for the record, the position assumed was the most comfortable

When I got the numbers I used the weight in grams (as far as I remember the touchpad weight is 780 g, while the iPad is 600 g, that's a 30% difference, as (obviously) 60 g = 10% and 60 * 3 = 180 so 10% * 3 = 30%. But I've just checked, the weight is actually 740 grams, it doesn't affect the result, since I converted it to newtons using pounds). This should also clarify why the salt 1 g vs .1 g and the 1,000% isn't really a counterexample (as the difference in the resulting Ns would be extremely small).


