A cruiser bike is a bike that gives an upright riding postion, is usually blinged out, and is ridden rather sedately.
MTBs are available in several different versions(XC, AM, DH), but basically they're about providing a compromise between ruggedness and rideability.
Mountain bikes have much knobblier tires and usually have suspension, which is rarely available on cruisers. Mountain bikes are also used competitively.
I have no idea what you mean by "gear bike", so the question can't be answered.
The difference is that the mountain bike tube is much burlier and wider than the dirt jump tube but may not be as strong in terms of hard hitting strength.
Mountain bike helmets are better than dirt bike helmets
Not particularly, 10 mph is below average sprinting speed. The record speed on a mountain bike is above 100mph.
Mountain bike
A DH bike is heavier, stronger, has a slacker steering angle and plusher suspension. The XC bike is lighter, more responsive, weaker and has less travel in its suspension.
Really depends on what you mean by a "regular bike". But road bikes tend to be lighter, more slender and focused more on speed than everyday usefullness compared to a regular bike.
There are a few good mountain bikes tires that would suit a 18 speed bike. I would go to a bike store and ask.there's different tires for what type of riding you doing but everyone have their own way they like their bikes from handle bars to tires. There's no best part. It's just what's good for you
The difference between a scooter and a pocket bike is the speed capability. The pocket bike is small in size but it can achieve speeds over 80 mph in some cases. The scooter has a governor that does not let it go past 45 mph in most cases, and the motor is not set up to run fast like the pocket bike.
A road bike offers a more preformance-oriented, streamlined hunched over riding position and bike design, while a cruiser bike has the rider more upright and is more set up for comfort than speed.
IMO there isn't that much practical difference between similarly priced bike computers. Find one with the features you want and a user interface you like and you're good to go.
Pick a gear that gives you the right ratio, then go for it. No difference than from a single-speed bike.