why are are rods, disks, spheres and rollers (Types of pebbles) distributed on a pebble beach like they are?

Question

Also why are these pebbles shaped like this? I take it their distribution has something to do with their shapes? Would like to hear answers from any geologists or geographers out there thanks.

Also why are these pebbles shaped like this? I take it their distribution has something to do with their shapes? Would like to hear answers from any geologists or geographers out there thanks.
Mainly talking about pebble and gravel beaches

Answer 1

Take a can of "Planters Mixed Nuts" and take out half the nuts and put in enough sunflower seeds to fill the can 90% full and cover and shake the can, it's the same phenomena. ;-)

Size of the object determines where it will end up. This is a known mathmatical result.

Answer 2

The rocks come from the rivers. Just look at all the wood that piles up during the rainy season even though there might not be any trees around. The beaches require rivers. If you dam up the rivers, the sand and rocks get washed out to sea. In California you will see man made rock formations that are there to trap the sand, because of the daming of the rivers. So basically the rocks were worn down when they were in the river, a rain came and washed them out to sea. The waves came along and pushed the sand and rocks against the shoreline and the scene repeated itself till the beach was formed. The waves come in on an angle so the push the sand down the coast. That's why you can have sand far away from a river.