Help with putting a box on a shelf (gravity?)

[asdfroy]

i am making a custom size card box filled with stuff that i want to put on top of a shelf (the box is bigger than the shelf), assuming the weight of the object is distributed evenly in the card box, what percentage of the box surface area (bottom of the box) that i need to have on the surface of the shelf, and the percentage that i can have floating by the edge of the shelf for the card box to not fall down.

thx

 

[Simon Bridge]

Welcome to PF;
The lynchpin here is to draw a diagram of the situation ... gravity acts downwards from the center of mass, so what happens if the line directly down from the center of mass of the box goes over the edge of the shelf? Compare with when it doesn't...
You can even get a small box and experiment.

After that you just need some assessment of how much disturbance the box is going to need to take.

 

[Dale]

assuming the weight of the object is distributed evenly

This is a dangerous assumption. I would make the box match the size of the shelf.

 

[berkeman]

This is a dangerous assumption. I would make the box match the size of the shelf.

Agreed. At the very least, I would use a thin rope to secure the box once it is on the shelf. Kind of like a variation of the securing bands in this picture:

https://s-media-cache-ak0.pinimg.com/736x/1c/16/70/1c1670afb724c26972c41df3334fe0e9.jpg