First of all, the rest of the cycling community calls the thing by the rear wheel for sprocket, and the thing by the pedals for chain ring or chain wheel - but I understand what you mean.
And only you can answer your original question, as it depends on how you want your bike to behave. If you want more top speed - go for a smaller sprocket. If you want quicker starts - go for a bigger sprocket. If you don't have one - read up on the specs for a bike for the type of riding you want to do - then get the same for your bike.
A tooth on a wheel gear is called a cog.
A cog is a mechanism that allows the transferral of energy from one site to another. A 'cog' is a single tooth on a gear wheel.
Guessing an 11T cog (sproket), maybe a custom 10T.
do you mean meat car? get tires, spring, empty meat tank, sprocket, and cog from degrassi knoll. then go to the hermitage and buy 1 sweet rims. meat paste the spring and sprocket together. then combine that with the cog.then combine a meat stack with the empty meat tank. then commbine that with the cog and sprocket assembly. then combine tires and rims. then combine dope wheels and meat engine
"would it go faster if i put a bigger cog on the back wheel" no, you need a smaller "cog" or sprocket on the back wheel to up the speed, but your still only looking at a 3% gain in top end speed. try a larger sprocket on the front eg. if you have a 15 tooth sprocket change it for a 16 or 17 tooth. this should give you up to about 10 to 15% gain at most. if you want a bit more then you'll need to look in to rejetting the carb, free flow airfilter, change the cdi for a race or unrestricted cdi, and a free flowing exhaust to help it all on it's way. but remember that even after all these mods your still only looking at a small top end gain, after all it's still a 125cc. if your looking to bring the speed up even more than you need to find a good big bore kit, but that's a lot of work and not one i'd recomened a novice to install.
You select a bigger rear cog. Whenever you see someone going up a hill on a bike they always seem to be pedaling faster than normal. With the cog on the back being bigger than the front the front cog spins faster than the rear. Im not sure how to explain why it makes it easier but a understanding of gear ratios may help you. Hope that answers some of your question.
You have to do a certain mission to unlock the head, then you beat the cog bosses which are like lvl 60 so you should bring lots of friends, but only sometimes do you unlock the parts of the body of the cog.
Depends on what kind of riding you want to do. It's probably too low for any kind of utility/distance riding but might be OK for dirt/trick riding.
I saw how a cog building is made. A cog that is walking down the street will choose what building he will turn a cog building into. He walks into that building and then it automatically turns into a cog building.
cog is a robot
a cog wheel is the main part that runs the cog entire body
A 2.0 version cog is a cog that when you destroy it, it will turn into a skelecog.