newton needs the time in seconds so you have to convert ticks to seconds. this gets done by diving by 16. for example 4 ticks -> 4 / 16 = 0.25 seconds.

i think the most common cause for simulations which somehow seem to look unrealistic is wrong scale. you have to keep in mind that we aren't used to look at collapsing stacks of crates which are more than a meter in diameter. we are used to toy bricks. this doesn't look the same.