An object sliding down a tube is subject to 3 kinds of forces. They are the force of gravity, the forces applied to the object by the tube and the force on the object due to its motion through the air. The force of gravity may be broken up into two parts, that pressing the object against the tube and that sliding the object along the tube. The forces applied by the tube are the force supporting the object's weight, which exactly balances the part of gravity pressing the object against the tube, and the force of friction opposing the sliding motion. The force of air resistance also opposes the sliding motion. The velocity of the object through the tube then will depend on these forces.
The tube's angle of elevation will affect how much of the force of gravity is holding the object against the tube surface and how much is causing the object to slide along the tube. The steeper the angle, the more of gravity which goes into sliding and the less into holding the object and the tube together, so the faster the object emerges from the tube.
The tube's material will determine how big the frictional force is for any given angle of elevation. The more friction, the slower the object emerges from the tube.
The tube's width will have an effect on the air resistance. If it fit closely around the object, the object would be like a piston in a cylinder, compressing the air in front of it causing more air resistance. If the fit is quite loose, air resistance will be small.
The tube's length will affect the velocity since for any given angle of elevation, the object will start from a higher position and unless the air resistance is very high, the object will accelerate all the way to the bottom, coming out with higher velocities for longer tubes. If the air resistance is high enough that the object reaches what is called its "terminal velocity", longer tubes will not add to speed.
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