I would say on the sociables, and this is just based on my incredible mechanical intelligence because I have not seen one. I would say the bike has a common shaft on the end of it is the drive chain to the wheel or wheels. Each person has a crank they are connected to the common driveshaft with a freewheel type sprocket. Then as they each pedal it spins the common shaft. Or it may be that one person (the dumb one) has pedals that drive it and all the smart ones just spin pedals with a chain that goes to a disconnected sprocket.
If you are on the second type and pedalling real hard then you are the dumb one.
Sociable just means side by side or abreast. There are many ways to do it. Think of Air Force trainers. Some have the instructor behind the trainee (T-38.) Some have the instructor and the trainee next to each other (T-37.)
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