1888a123_Beginner_Dirt_Bike___GICL_Wiki_Dirt_Bike_Parts_List_Function
[Part and Quantity] Muffler System (1) [Part Number] DR70-124 [Materials] Whole part is metal, most likely steel. Steel would be used because of its high strength and cheap cost [Forces] The only forces applied would be the air flowing through the system. On straight parts, this would result in very little force. Where the tubing turns, the forces would depend on the pressure, temperature, and velocity of the exhaust [Manufacturing Process] The main system was manufactured by heating steel tubing and then bending it. The outer pans where metal extrusions and then bending. These parts were then welded together. [Shape] The shape is needed to do the purpose. The turns are needed to slow the velocity of the air. The length of the part is also needed to make sure the exhaust is directed far enough from the engine and the rider. [Part Complexity] 3 [Function] 
Functional: Takes exhaust from engine and releases it at the rear of the bike. Helps to minimize noise from the engine.
Group 11 - Beginner Dirt Bike - GICL Wiki